BASIC CHEMISTRY 1 MID TEST

RENI DESRINOFITA
RSA1C112006

1. X pure material is solid at room temperature. if the substance is heated to 230 C melted gradually. if it is then cooled to room temperature, the liquid can not be frozen.
   a. that x may be from an element or compound. explain it!
   b. Is it a chemical change occurs? if so could be said to undergo change endotherm, based on the information provided?
  c.can said that the liquid is an element, based on the information providedAnswer:

  a. X in the above matter is a compound, because the compound is a combination of several elements that have the same properties.While the element is a collection of some of the same atoms that have the same properties, because the number of neutrons is the same. In the matter of the above mentioned that the substance melted at some stage, while the elements that can not be divided again with any chemical reaction, so we can conclude that X is a compound.

  b. In the X chemical changes, because chemical changes occur when marked by several changes, such as changes in color, temperature, precipitation occurs and there are gas bubbles. In X temperature change from room temperature is at 25 C to 230 C means the X chemical changes.The reaction involves the endothermic reaction into endothermic reactions occur because the temperature change of the environment to the system.

  c. Yes, because it is a constituent element of a compound. Based on the above information, including fluid into the elements, because water is a constituent element of H and O.

2. When the candle that weighs 10 g burned in oxygen, carbon dioxide and water vapor formed by the combustion of more than 10 g weight. This was the case in accordance with the law of conservation of mass. Explain!Answer:
Law of conservation of mass expressed by Antoine Laurent Lavoisier (1743-1794), which reads: "In a reaction, the mass of substances before and after the reaction is the same", in other words, the mass can not be created and can not be destroyed. This means that as long as there is no reaction occurs atoms reactants and reaction products were missing.Understanding different mass with weight terms. The mass of an object, in all places always remain, while the severity depends on the local force of gravity.In the above case before the burning substance is 10 g weight while after severe reaction to a substance into 10 g more, so that changes is the weight of the substance but its mass will not change.
3. When carbon burns under a limited amount of oxygen, it forms two gaseous compounds. Suggest ways to diffrerentiate two compounds with one another.Answer:
Doing qualitative research or experiments of the experiment we can find the difference between the two gas.Or it can also be determined by determining the constituent elements of the substances we eat will know the difference of the two substances.
4. After mendeev preparing the periodic table, he concluded that the atomic weights of some elements was the wrong decision, and this conclusion appears to be true. How mendeelev able to predict some of the atomic weights is wrong? why his predictions are not always right. Explain!Answer:

In 1869 a Russian scholar named Dmitri Ivanovich Mendeleev, based on observations of 63 elements known at the time, concluded that the properties of elements are a periodic function of the relative atomic mass. That is, if the elements are arranged according to their relative atomic mass increases, the specific properties will be repeated periodically. Mendeleev placed elements that have similar properties in vertical columns called class. Row-column horizontal line element that increases the relative atomic mass, called the Mendeleev periodic period in 1872 published a list displayed on the table.
Many other elements grouping ideas proposed but did not satisfy the scientific community at the time. However, the theory proposed by Dmitrij Ivanovich Mendeleev Russian chemist (1834-1907), and independently by the German chemist Julius Lothar Meyer (1830-1895) in contrast to other proposals, and more persuasive. Both have the same outlook as follows:
The views Mendeleev and Meyer
List the elements that exist at that time may not be comprehensive.
Expected properties of elements vary systematically. So the nature of the element of the unknown can be predicted.
Originally Mendeleev theory failed to attract attention. However, in 1875, indicated that the new element gallium was discovered by French chemist Paul Emile Lecoq de Boisbaudran (18,381,912) was not the other is the existence of eka-aluminum and its been predicted by Mendeleev. Thus, the significance of the theory of Mendeleev and Meyer slowly accepted. Table 5.2 provides properties for elements predicted by Mendeleev, who was not yet known and the nature of germanium ekasilikon discovered by German chemist Clemens Alexander Winkler (1838-1904).

Mendeleev published a table that can be considered as the origin of the modern periodic table. In preparing the table, Mendeleev initially arrange the elements in order of atomic mass, as well as its predecessor. However, he stated keperiodikan nature, and sometimes reorder the elements, resulting in reverse order of atomic mass.
Furthermore, the situation is complicated because the procedure to determine the mass of the atom has not been standardized, and sometimes chemist might use a different atomic mass for the same element. This dilemma is slowly resolved after the International Chemical Congress (Congress was held in 1860 in Karlsruhe, Germany. Goal of the Congress is to discuss the unification of atomic mass. Cannizzaro to take this opportunity to introduce Avogadro's theory.) First attended by Mendeleev, but difficulties remains.The periodic table is continuously growing element after Mendeleev periodic table is proposed. Meanwhile, there is a variety of problems. One important issue is how to handle the noble gases, transition elements and rare earth elements. All these issues are properly resolved and made the periodic table are more valuable. The periodic table, chemical scripture, should be referred to regularly.
New class of noble gases easily inserted between the positive elements that are highly reactive, alkali metals (group 1) and negative elements are very reactive, halogen (group 7).
Accommodated the transition metal element in the periodic table by inserting a long period although not very clear rationale. The real problem is lantanoid. Lantanoid treated as an element of the "extras" and placed marginally outside the main part of the periodic table. However, the actual procedure does not resolve the main problem. First, why is there an extra element is unclear, even more of a puzzle is the question: is there a limit of the number of elements in the periodic table? Because there are elements that are very similar, it is difficult to decide how many elements can exist in nature.
Bohr theory and experiment Moseley generate theoretical resolution of these problems. Explanation of the periodic table of the first period to the third period can be explained by the theory of electron configuration described in chapter 4. The first period (1H and 2HE) associated with the process of entering the 1s orbital. Similarly, the second period (from 3Li to 10Ne) associated with filling the 1s, 2s and 2p, and the 3rd period (from 11Na to 18Ar) associated with filling the 1s, 2s, 2p, 3s and 3p.
Period begins the period-4. The explanation for this is due to their drastically different d orbitals of the circle, and so the 3d electron energies even higher than 4s. Consequently, the period-4, the electrons will fill the 4s orbital (19K and 20Ca) as soon as the 3s and 3p orbitals, 3d orbitals jump. Then the electrons begin to occupy the 3d orbitals. This process is related to the ten elements of 21Sc to 30Zn. The process further 4p orbitals are related to the six elements of 31Ga to 36Kr. This is the reason why the period-4 contains 18 elements instead of 8. 4f electron orbital energies much higher than 4d orbitals and thus the 4f electrons do not play a role in the period of the four elements.
Period-5 is similar to the period-4. The electrons will fill orbitals 5s, 4d and 5p in this order. As a result, the period-5 will have 18 elements. 4f orbitals are not involved and this is the reason why the number of elements in the 5 is 18.
The number of elements to be included in period-6 are 32 reasons involved 7 × 2 = 14 elements related to the 4f orbitals. Originally 6s electrons fill orbital (55Cs and 56Ba). While there are miraculous exceptions, elements from 57La to 80Hg associated with 4f orbitals and then 5d. Lantanoid series (up 71Lu) rare earth elements associated with the 4f orbitals. After this process, the six main group elements (81Tl to 86Rn) to follow, this is related to 6p orbitals.
Period-7 began with the 7s orbitals (87Fr and 88Ra) followed by the 5f orbitals produce aktinoid series of rare earth elements (from 89Ac to element No. 103). World elements will spread further, but in between the elements that exist naturally, the element with the largest atomic number is 92U. Elements after 92U is made elements with a very short half-lives. It is difficult to foresee an extension of this kind of list elements, but it is likely the new element will be very short half-life.

5. When the mercury chloride solution is added a solution of silver nitrate, a white solid forms. Identification of a white solid and write a balanced equation for the reaction that occursAnswer:

HgCl2 + 2AgNO3 ---> Hg (NO3) 2 + 2AgClThe resulting white powder is silver nitrate (AgNO3)

THE STRUCTURE OF ATOM AND PERIODIC TRENDS (CH 7)

In the SparkNote on the Periodic table we discussed a number of simple periodic trends. In this section we will discuss a number of more complex trends, the understanding of which relies on knowledge of atomic structure.

Before getting into these trends, we should engage a quick review and establish some terminology. As seen in the previous section on the octet rule, atoms tend to lose or gain electrons in order to attain a full valence shell and the stability a full valence shell imparts. Because electrons are negatively charged, an atom becomes positively or negatively charged as it loses or gains an electron, respectively. Any atom or group of atoms with a net charge (whether positive or negative) is called an ion. A positively charged ion is a cation while a negatively charged ion is an anion.

In the modern periodic system of horizontal rows are called periods and upright rows are called groups. The number of periods in the periodic system there are 7 and marked with numbers:• Period 1 is referred to as the period is very short and contains 2 elements• Period 2 is referred to as short a period and contains 8 elements• Period 3 is referred to as short a period and contains 8 elements• Period 4 called the period length and contains 18 elements• Period 5 called the period length and contains 18 elements• Period of six called the period is very long and contains 32 elements, in this period there are elements of the Lanthanide element number 58 to number 71 and placed on the bottom• Period 7 is referred to as the period is not yet complete because it may increase the number of elements that occupy it again, until now contains 24 elements. In this period there is a row of elements called Actinides, that is, elements numbered 90 to 103 and the number placed on the bottom.
The number of groups in the periodic system are 8 and marked with Roman numerals. There are two major categories, namely class A (main group) and class B (class transitions). Group B is located between groups IIA and IIIA groups.
The names of the classes to the element of class A• Group IA alkali group called• Group IIA alkaline earth group called• Type IIIA called boron golonga• Group IVA called carbon groups• Group VA called nitrogen group• VIA Group called the oxygen group• Group VIIA group called halogens• Group VIIIA group called noble gases
In the period 6 class IIIB there are 14 elements that are very similar, the lanthanide elements. In the period 7 also apply the same thing and called the actinide elements. Both series of elements called transition elements inside.
The elements of the lanthanide and actinide belonged IIIB, included in thegroup because it has very similar properties.
Among the elements of group IIA and IIIA are ten column elements of group B. These elements are called transition elements. The term transition means the transition, ie the transition from block to block p s. Transition elements are defined as elements that have subshell d or f subshell partially filled. For example, copper has the electron configuration [Ar] 3d10 4S1. Transition elements contained in the d-block elements are having an unfilled d subshell full. As a result, the transition elements have several distinctive properties, namely:
1. All the elements of the transition metal is hard to boiling point and high melting point.2. Each transition elements have multiple oxidation states, except for group IIB and IIIB elements. For example, vanadium, has the oxidation state of +2 to +5.3. Compounds of transition elements are usually colored and paramagnetic. All of the properties due to the configuration of electrons in d orbitals is not fully charged

Now we are ready to discuss the periodic trends of atomic size, ionization energy, electron affinity, and electronnegativity.

Atomic Size (Atomic Radius)

The atomic size of an atom, also called the atomic radius, refers to the distance between an atom's nucleus and its valence electrons. Remember, the closer an electron is to the nucleus, the lower its energy and the more tightly it is held.

Moving Across a Period

Moving from left to right across a period, the atomic radius decreases. The nucleus of the atom gains protons moving from left to right, increasing the positive charge of the nucleus and increasing the attractive force of the nucleus upon the electrons. True, electrons are also added as the elements move from left to right across a period, but these electrons reside in the same energy shell and do not offer increased shielding.

Moving Down a Group

The atomic radius increases moving down a group. Once again protons are added moving down a group, but so are new energy shells of electrons. The new energy shells provide shielding, allowing the valence electrons to experience only a minimal amount of the protons' positive charge.

Cations and Anions

Cations and anions do not actually represent a periodic trend in terms of atomic radius, but they do affect atomic radius, and so we will discuss them here.

A cation is positively charged, meaning that it is an atom that has lost an electron or electrons. The positive charge of the nucleus is thus distributed over a smaller number of electrons and electron-electron repulsion is decreased, meaning that the electrons are held more tightly and the atomic radius is smaller than in the normal neutral atom. Anions, conversely, are negatively charged ions: atoms that have gained electrons. In anions, electron-electron repulsion increases and the positive charge of the nucleus is distributed over a large number of electrons. Anions have a greater atomic radius than the neutral atom from which they derive.

Ionization Energy and Electron Affinity

The process of gaining or losing an electron requires energy. There are two common ways to measure this energy change: ionization energy and electron affinity.

Ionization Energy

The ionization energy is the energy it takes to fully remove an electron from the atom. When several electrons are removed from an atom, the energy that it takes to remove the first electron is called the first ionization energy, the energy it takes to remove the second electron is the second ionization energy, and so on. In general, the second ionization energy is greater than first ionization energy. This is because the first electron removed feels the effect of shielding by the second electron and is therefore less strongly attracted to the nucleus. If a particular ionization energy follows a previous electron loss that emptied a subshell, the next ionization energy will take a rather large leap, rather than follow its normal gently increasing trend. This fact helps to show that just as electrons are more stable when they have a full valence shell, they are also relatively more stable when they at least have a full subshell.

Ionization Energy Across a Period

Ionization energy predictably increases moving across the periodic table from left to right. Just as we described in the case of atomic size, moving from left to right, the number of protons increases. The electrons also increase in number, but without adding new shells or shielding. From left to right, the electrons therefore become more tightly held meaning it takes more energy to pry them loose. This fact gives a physical basis to the octet rule, which states that elements with few valence electrons (those on the left of the periodic table) readily give those electrons up in order to attain a full octet within their inner shells, while those with many valence electrons tend to gain electrons. The electrons on the left tend to lose electrons since their ionization energy is so low (it takes such little energy to remove an electron) while those on the right tend to gain electrons since their nucleus has a powerful positive force and their ionization energy is high. Note that ionization energy does show a sensitivity to the filling of subshells; in moving from group 12 to group 13 for example, after the d shell has been filled, ionization energy actually drops. In general, though, the trend is of increasing ionziation energy from left to right.

Ionization Energy Down a Group

Ionization energy decreases moving down a group for the same reason atomic size increases: electrons add new shells creating extra shielding that supersedes the addition of protons. The atomic radius increases, as does the energy of the valence electrons. This means it takes less energy to remove an electron, which is what ionization energy measures.

Electron Affinity

An atom's electron affinity is the energy change in an atom when that atom gains an electron. The sign of the electron affinity can be confusing. When an atom gains an electron and becomes more stable, its potential energy decreases: upon gaining an electron the atom gives off energy and the electron affinity is negative. When an atom becomes less stable upon gaining an electron, its potential energy increases, which implies that the atom gains energy as it acquires the electron. In such a case, the atom's electron affinity is positive. An atom with a negative electron affinity is far more likely to gain electrons.

Electron Affinities Across a Period

Electron affinities becoming increasingly negative from left to right. Just as in ionization energy, this trend conforms to and helps explain the octet rule. The octet rule states that atoms with close to full valence shells will tend to gain electrons. Such atoms are located on the right of the periodic table and have very negative electron affinities, meaning they give off a great deal of energy upon gaining an electron and become more stable. Be careful, though: the nobel gases, located in the extreme right hand column of the periodic table do not conform to this trend. Noble gases have full valence shells, are very stable, and do not want to add more electrons: noble gas electron affinities are positive. Similarly, atoms with full subshells also have more positive electron affinities (are less attractive of electrons) than the elements around them.

Electron Affinities Down a Group

Electron affinities change little moving down a group, though they do generally become slightly more positive (less attractive toward electrons). The biggest exception to this rule are the third period elements, which often have more negative electron affinities than the corresponding elements in the second period. For this reason, Chlorine, Cl, (group VIIa and period 3) has the most negative electron affinity.

Electronegativity

Electronegativity refers to the ability of an atom to attract the electrons of another atom to it when those two atoms are associated through a bond. Electronegativity is based on an atom's ionization energy and electron affinity. For that reason, electronegativity follows similar trends as its two constituent measures.

Electronegativity generally increases moving across a period and decreases moving down a group. Flourine (F), in group VIIa and period 2, is the most powerfully electronegative of the elements. Electronegativity plays a very large role in the processes of Chemical Bonding.

THE STRUCTURE OF ATOM (Ch 6)

The structure of an atom is the basic unit of matter consisting of a nucleus and its negatively charged electron cloud surrounding it. The nucleus contains a mix of positively charged protons and electrically neutral neutrons (except in Hydrogen-1 which has no neutrons). The electrons in an atom bound to the nucleus by the electromagnetic force. Similarly, a collection of atoms can bind to each other to form a molecule. Atoms containing the number of protons and electrons of the same neutral, while containing the number of protons and electrons of different positive or negative and is ion. Atoms are grouped based on the number of protons and neutrons in the atomic nucleus. The number of protons in an atom determines the chemical element the atom, and the number of neutrons determine the isotope of the element. 
PARTICLE MATERIALThe smallest part of matter called particles.Some opinions about particles of matter:1. According to Democritus, the distribution of matter is discontinuous (if the material is divided and continues to be divided then finally obtained the smallest particle that could no longer be divided = called Atom)2. According to Plato and Aristotle, the distribution of matter is continuous (division can continue indefinitely)Basic Postulates of Dalton Atomic Theory:1) All matter is composed of minute particles called atoms2) The element is composed of material similar atoms3) Atoms of an element are identical but different from atoms of other elements (having different masses)4) The compound is a material consisting of two or more types of atoms with a certain ratio5) Atoms can not be created or destroyed and can not be converted to other atoms through chemical reactions normal. The chemical reaction is the rearrangement (reorganization) of the atoms involved in the reaction
 The downside of Dalton Atomic theory postulates:1) Atom is not something that is not divided, but rather made up of subatomic particles2) Atoms of the same element may have different masses (called isotopes)3) Atoms of an element can be changed into atoms of other elements through nuclear reactions4) Some of the elements are not made up of atoms instead of molecules 
ATOMIC THEORY DEVELOPMENT1). Atomic Model Daltona) Atom described as a very small solid ball.b) Atoms are the smallest particles that can not be broken again.c) Atoms of an element have the same same, while the atoms of different elements, different in mass and nature.d) Compounds are formed when atoms combine with each other.e) A chemical reaction is the reorganization of atoms, so there is no atom has changed due to chemical reactions.
 Dalton's atomic theory is supported by the second law of nature, namely:1. Law of Conservation of Mass (Lavoisier law): the mass of substances before and after the reaction is the same.2. Keep Comparative Law (law Proust): comparison of mass elements that make up a substance is fixed.Weakness Atomic Model Dalton:1) Can not explain the difference between a single atom elements with other elements2) Can not explain the electrical properties of materials3) Can not explain how atoms bond together4) According to Dalton's atomic theory of number 5, no atom has changed due to chemical reactions. Now it turns out the reactions of nuclear chemistry, an atom can change into other atoms.2). Thomson Atomic ModelAfter the discovery of the electron by JJ Thomson, Thomson atomic model formulated which is a refinement of the atomic model of Dalton. According to Thomson:a) Atoms consist of a positively charged material and in which the electrons are scattered (like raisins in raisin bread)b) Atoms are neutral, the positive charge and negative charge the same amount
 3). Rutherford Atom Modela) Rutherford found evidence that the atomic nuclei are positively charged, are smaller than the size of the atomic mass of an atom but almost entirely from the point masses.b) Atoms consist of a positively charged nucleus and are at the center of the atom and the electrons move through the nucleus (like planets in the solar system).c) Atoms are neutral.d) The radius of the nucleus and atomic radii can be determined.Weakness Rutherford Atomic Model:Ø Inability to explain why the electrons do not fall into the nucleus due to electrostatic attractive forces the core to the electron.Ø According to Maxwell's theory, if the electrons as charged particles around the core that has the opposite charge then the trajectory will spiral and will lose power / energy in the form of radiation and eventually fell to the core.4). Niels Bohr Atom Model• atomic model based on quantum theory to explain the spectrum of hydrogen gas.• According to Bohr, the line spectrum indicates that the electrons only occupy certain energy levels in the atoms.He said:a) Atoms consist of a positively charged nucleus and the surrounding circulating electrons are negatively charged.b) Electrons orbit around the nucleus of an atom in a particular orbit known as the stationary state of motion (fixed), hereinafter referred to as the main energy level (electron shell), which is expressed by the principal quantum number (n).c) During the electrons are in a stationary orbit, its energy will remain so no light is emitted.d) The electrons can only move from the lower stationary trajectory to a higher stationary trajectory if absorbing energy. Conversely, if the electrons move from a higher stationary trajectory to lower the release of energy.e) In the normal state (without outside influence), the electrons occupy the lowest energy level (called the basic level = ground state)Niels Bohr Atom Model Weaknesses:1. Just to explain the spectrum of the atom or ion containing one electron and is not in accordance with the spectrum of electron atoms or ions that much.2. Not being able to explain that atoms can form molecules through chemical bonds5). Modern Atomic ModelDeveloped based on the theory of quantum mechanics is called wave mechanics; initiated by 3 experts:a) Louis Victor de BroglieStating that the material has the properties of a material dualism, and as waves.b) Werner HeisenbergPut forward the principle of uncertainty for the material is of a particle and a wave. Distance or location of electrons that surround the nucleus can only be determined by the possibility - probability alone.c) Erwin Schrodinger (refining models Bohr Atom)Successfully prepared for electron wave equation using the principle of wave mechanics. Electrons surrounding the nucleus contained in an area that is 3-dimensional orbital around the nucleus where electrons with a specific energy can be found with the greatest possible.Modern atomic models:a) Atoms consist of a nucleus containing protons and neutrons while the electrons moving around the nucleus and are at particular orbitals of atoms that make up the skin.b) the area of ​​the 3-dimensional orbital around the nucleus where electrons with a specific energy can be found with the greatest possible.c) The position of electrons in the orbital-orbital quantum numbers stated.• Orbital described as a cloud of electrons, namely: the forms of space where an electron is likely to be found.• The meeting of the electron cloud, the more likely the electron was discovered and vice versa.

Energy and chemical reaction "enthalpy" (Ch 5)

Enthalpy is a term in thermodynamics that states the amount of internal energy of a thermodynamic system plus the energy used to do work. Enthalpy can not be measured, which can be calculated is the value changes. Mathematically, the enthalpy change can be formulated as follows:ΔH = ΔU + PΔVwhere:• H = enthalpy of the system (joules)• U = internal energy (joules)• P = pressure of the system (Pa)• V = volume of the system ()

1. System and environmentThe system is at the center of everything we learn concern the energy changes. While the so-called environment is everything outside the system. Example: The reaction between zinc metal with a solution of hydrochloric acid (HCl) in a test tube is accompanied by the emergence of gas bubbles.
In the example above the center of attention is the metal zinc and HCl. Thus, zinc metal and HCl solution called the system, while the test tube, air temperature, air pressure is the environment. Based on interaction with the environment, the system can be divided into three kinds, namely:a. Sitem Open, a system that allows the exchange of heat and matter (material) between the environment and the system.b. Closed system, a system which allows the exchange of heat between the system and its environment, but not an exchange of material.c. Isolated Systems (sealed), a system that does not allow the exchange of heat and matter between the system and the environment.

2. Energy and enthalpyIn any chemical reaction is always a change of energy.Energy units:1 calorie = 4.184 Joules1 kJ = 1000 Joules1 kcal = 1000 calories1kkal = 4.184 k JOverall energy possessed by a system in a particular state is called energy (U). Energy in a state function, depends only on the state of the system (temperature, volume, pressure, and number of moles), does not depend on the path through the system. Energy can not be measured but the changes can be measured. If the change occurs at a constant pressure (open system), the energy changes that occur in the so-called enthalpy change.
Chemical reactions are generally carried out in an open system (fixed pressure).Therefore, in any process that involves a change in volume due to constant pressure, there is the work that accompanies the process although a small but significant.According to the Law of Thermodynamics I (Law of Conservation of Energy),H = U + PVThe enthalpy change is expressed by the equation:H = U + PVFrom the equation it can be concluded that if the reaction is carried out at a constant pressure the heat changes that occur will be equal to the enthalpy change for the pressure change 0 (Zero). Thus, the enthalpy equal to the amount of energy stored in a system. So the enthalpy (H) is the energy stored in the form of heat in a system.
3. Enthalpy changeThe enthalpy change of a system can be measured if the system is changing.Enthalpy changes (H):If a reaction takes place at a constant pressure, the change in enthalpy equalthe heat that must be removed from the system into the environment or otherwise thattemperature of the system back to its original state.H = qp (qp = heat of reaction at constant pressure)The magnitude of the enthalpy change is the difference in magnitude of the enthalpy of the system after a change in the magnitude of the enthalpy of the system before the changes at a constant pressure.H = Hakhir - HawalThe enthalpy change accompanying a reaction is influenced by:• The number of substances• physical state of a substance• Temperature (T)• Pressure (P)
4. Reaction was exothermic and endothermic reactions1. Exothermic reaction is a reaction that releases heat or energy.Enthalpy reduced system (the reaction products have a lower enthalpy than the original substance).H final <H initialH final - H initial <0H negative valueExample:The reaction between calcium oxide (quicklime) and Cretaceous shallow water put into the water in a test tube. This reaction takes place is characterized by a mixture of temperature rise (the system). Because the temperature of the system is higher than the environment, the heat will come out of the system into the environment until they become the same temperature.CaO (s) + H2O (l) Ca (OH) 2 (aq)
2. Endothermic reaction is a reaction that absorbs heat or energy needs.Enthalpy system is improved (the reaction has a higher enthalpy than the original substance).H final> H initialH final - H initial> 0H positive valueExample:The reaction between barium hydroxide crystals oktahidrat with ammonium chloride crystals.When barium hydroxide crystals oktahidrat, Ba (OH) 2. 8H2O crystals mixed with ammonium chloride (NH4Cl), the reaction takes place immediately marked by a drop in temperature and the formation of a mixture of ammonia gas. Therefore temperature of the mixture (the system) will be lower than the environment, the heat will flow from the environment into the system until they become the same temperature. Ba (OH) 2. 8H2O (s) + 2NH4Cl BaCl2.2H2O (s) + 2NH3 (g) + 8H2O (l)
5. Thermochemical EquationsThe equation that describes the reaction with the information about the change in enthalpy (heat). Because enthalpy is extensive properties (value depends on the magnitude and size of the system) then the thermochemical equation also listed the number of moles of a substance expressed reaction coefficient, and the phase state of the substance involved.Example:a. In the formation of 1 mol of water from hydrogen gas with oxygen gas at 25 ° C(298 K), 1 atm, was 286 kJ of heat is released.Thermochemical equations of the above statement isThe word "released" state that quite exothermic reaction. Therefore, theH = -286 kJ per mole of water formed.H2 (g) + O2 (g) H2O () H = -286 kJor,2H2 (g) + O2 (g) 2H2O () H = -572 kJ
b. The reaction of carbon and hydrogen to form 1 mole of C2H2 at temperatures of 25oCand a pressure of 1 atm requires 226.7 kJ of heat.Termokimianya equation:The word "need" states that belong to endothermic reactions.2 C (s) + H2 (g) C2H2 (g) + H = 226.7 kJ
6. Standard enthalpy change (Ho)Reaction enthalpy changes measured at 25oC temperature (298 K) andpressure of 1 atm was agreed as the standard enthalpy change, otherwisewith the symbol HoThe state standard is needed because measurements at different temperatures and pressures will result in prices that different enthalpy changes. Units used to express the change in enthalpy is kJ. Changes in molar enthalpy is kJ / mol.
Enthalpy change based on the type of chemical changes that occur:1. Standard enthalpy change of formation (Hf o)(Hf o = standard enthalpy of formation)Is the enthalpy change for the formation of 1 mole of a compound from its elements are the most stable, the standard state. Unit change in standard enthalpy of formation according to the International System (SI) is kJ / mol.Example:Changes from the standard enthalpy of formation of carbon dioxide (CO2) is -393.5 kJ / mol.Termokimianya equation:C (s) + O2 (g) CO2 (g) Hfo = -393.5 kJ / mol
2. Standard enthalpy change of decomposition (Hd o)(Hd o = standard enthalpy of decomposition)Is the enthalpy change for the decomposition of 1 mole of a compound into its elements, the standard state.Example:Enthalpy change for the decomposition of H 2 O is +286 kJ / mol.Termokimianya equation:H2O () H2 (g) + O2 (g) Hdo = + 286 kJ / mol
3. Standard enthalpy change of combustion (Hc o)(Hc o = standard enthalpy of combustion)Is the change in enthalpy in the combustion of 1 mol element or compound at standard conditions. Combustion is the reaction of a substance with oxygen