Calorimetry

Calorimetry is a way scientific expriment to figure the energy released or absorbed by a reaction. In calaorimetry, we use a calorimeter, that is composed by a system (chemical reaction) and surroundings (water or something like water).  When the reaction measures a made. and the asusmpition the THERMAL ENERGY CHANGE IS EQUAL TO THE CHANGE IN ENTHALPY, SINCE THE ENERGY LOST OR GAINED BY THE SYSTEM IS EQUAL TO THE ENERGY GAINED OR LOST BY THE SURROUNDINGS.
Don;t forget that when the question gives you the mass of the calorimeter, and its a metal. You must account it as one of the surroundings, which means that not only water is present.

Heat Transfer and Calorimetry

Kinetic energy and Potential energy are actually related! They also have specific calculation for each one of them. 

Kinetic energy is related to temperature. Therefore, Ek is related to thermal changes. To figure out what is the thermal change in a substance, consequently Ek.

Q = mc^t

Q means thermal change

M means mass

c mens specific heat capacity

^t means the change in temperature.

When we are talking about potential energy, we talk about enthalpy. Enthalpy is the total energy of a substance so Ek and Ep. When we say that there is a change in enthalpy, we talk about the difference between the Ep of the products and reactants.  REMEMBER THAT CHANGE IN ENTHALPY DOES NOT HAVE ANYTHING TO DO WITH CHANGE IN TEMPERATURE. 

Molar change in enthalpy - Change in the Ep per mole of a substance.

To figure the Enthalpy change, we always look at the calculalio ^^H= n^^Hm

^^^H means enthalpy change 

n means moles 

^^Hm means molar enthalpy change

The molar enthalpy of FORMATION will be listed on you r data booklet, The molar enthapy of DECOMPOSITION is the same of the formation, but with a reversed sign. For the other reaction, like combustion, it will be said in the question, or you will have to figured it out.  The molar enthalpy of elements is 0. 

Thermochemical Changes - Intro

Energy

The scientific definition of energy describes it as the ability to do work. Without energy, no reactions could occur, therefore, our lives would be impossible to continue. ALL ENERGY ORIGINATES FROM THE SUN! 

In this unit we will study the two types of energy that are extremely related to chemical changes and reactions: Kinetic and Potential Energy.

1) Kinetic:

It is an energy that is related to movement,  and in the case of chemistry, we will be talking about the movement of particles and molecules. Therefore, we will understand that when particles, or molecules, are moving faster, their kinetic energy is increasing. When moving slower, their kinetic energy will decrease. 

Kinetic Energy is very related to temperature. When a substance increases its temperature, it means that the particles are moving fast, therefore, we must have a large kinetic energy. The opposite occurs, when the temperature of a substance decreases.

As we know from previous studies, temperature gives us clues of heat. What is heat? Heat is the transfer of thermal energy between two substance or objects. 

2) Potential:

This energy is related to the bonds of molecules in a substance, when they are formed or broken down, potential energy is changed. In this units, we will focus on the potential energy in the intra molecular bonds, which are of course the bonds between atoms that form a molecule. When this bonds are broken down, or formed, that means that a chemical change, or we can say, a chemical reaction is occurring. 

There are two types of chemical reactions: Endothermic and Exothermic Reactions. 

Endothermic reactions are chemical reaction which energy is required in other to occur. The best example of endothermic reaction is PHOTOSYNTHESIS. Exothermic reaction in another hand is the chemical reaction that releases energy. The best example of exothermic reaction is CELLULAR RESPIRATION. 

Balancing Equations - Acidic and Basic Solutions

When we take in account reactions that are acidic or basic, we must consider the hydrogen ion and hydroxide ion. The overall approach regarding balancing these equation is very similar to a simple reaction, however, few more steps are required.

1. Write the unbalanced equation that show the formulas of the given reactants and products.
2. Balance the atoms other than oxygen and hydrogen.
3. Balance the atoms of Oxygen by adding water.
4. Balance the hydrogen atoms by adding hydrogen ions. (At this point, if we are dealing with an acidic solution, balance the charges by adding the electrons.)
5. If we are dealing with a basic solution: Add to both sides, the same number of hydroxide ions as the number or hydrogen ions present.
6. Add the hydrogen and hydroxide ions on the same side to form water.
7. Cancel and water molecule present on both sides of the reaction.
8. Balance the charges by adding the electrons.

Redox Reactions

Law of Conservation of Energy:

No energy is created, nor destroyed, it is transformed or transferred.

Yes, and in a chemical reaction? aren't there like several exchange of electrons?

If each atom or ion of a chemical reaction is oxidized, that another must be reduced. When this happens we have a redox reaction.

Redox reactions are not a type of reaction, like formation, or decomposition. 

Actually, all the types of reactions may be redox reactions.

To understand this concept better let's use this simple single-replacement reaction:

Zn(s)+CuSO4(aq)=Cu(s)+ZnSO4(aq)

Lets take away the spectators, which, in this case are the SO4 ions.

You obtain 

Zn(s) + Cu+2(aq) = Cu(s)+Zn+2 

As you see, Zinc lost electrons, it became positive, thus got oxidized. Copper, gained two electrons, since it was a cation and became a single atom. Therefore it was reduced. 

Well, we know that the electrons ran away from Zn to Cu, so what do we do about it?

Zinc is called the reducing agent, the one that donated electron, and the one the underwent oxidation, while copper is the oxidizing agent, the one that accepeted electrons, undergoes reduction.

Reduction

So, do you remember that little law of thermodynamics? What was it?

Energy is never created, or destroyed, it is always transformed...

...or transferred. 

When one atom, ion, or molecule, loses a electron, this little particle cannot just run around the environment. He needs a place to stay, a house. And what kind of house am i talking about?

Another atom, ion, or molecule.

Yes, they must gain the electrons that were lost by other elements that got oxidated. 

If oxidation is the loss of electrons, than, the gain of them is called reduction.

Oxidation

Okay! So, now let's look a little bit forward onto chemical reaction.

Our first topic is Oxidation.

Back in the days, chemists believed that oxidation was any reaction that occurred between any atom or compound with a molecular oxygen. 

However, after many and many years of study and analysis, it was learned that same reaction between atoms or compounds with other elements have similarities with those reaction involving oxygen. 

So the scientist came out with another definition for oxidation, which is the loss of electrons by an atom or an ion.

For example, when Mg(s) reacts with Cl2(g), our little buddy Magnesium atom loses electrons, becoming a cation. We can say, therefore, that Magnesium got oxidised.