When a reaction is exothermic ("exo-" meaning out and "-thermic" having to do with heat), it means that the reaction is giving off heat into the environment. Therefore, the reactants have a net heat loss throughout the process of the reaction.

The change in enthalpy, , is a measure of the change in heat energy during a reaction.  is always negative for an exothermic process because the products always have less heat energy than the reactants.

When a reaction is exothermic ("exo-" meaning out and "-thermic" having to do with heat), it means that the reaction is giving off heat into the environment. Therefore, the reactants have a net heat loss throughout the process of the reaction.

The change in enthalpy, , is a measure of the change in heat energy during a reaction.  is always negative for an exothermic process because the products always have less heat energy than the reactants.

An exothermic reaction releases energy into the environment. In contrast, endothermic reactions require an input of energy to initiate the reaction.

Forming a bond is always an exothermic reaction because it releases energy. Breaking a bond always requires energy, and is thus an endothermic process. Synthesis, decomposition, and single-replacement reactions can be either exothermic or endothermic, and cannot be determined without more information.

Spontaneity is determined by Gibbs free energy. When Gibbs free energy is less than zero, the reaction is considered exergonic and will occur spontaneously. When Gibbs free energy is greater than zero, the reaction is considered endergonic and will not occur spontaneously.

Exothermic reactions cause a release of enthalpy (heat) from the system and endothermic reactions require and input of energy to initiate the reaction. Gibbs free energy is determined by enthalpy, entropy, and temperature. A negative enthalpy, high temperature, and high entropy will cause the reaction to be more spontaneous, but must all come together to contribute. Simply because a reaction is exothermic does not meant that is increases entropy enough to be spontaneous.

The enthalpy of  describes the amount of heat when the amount of carbon in the balanced reaction (two moles) is used. Since only  of carbon are used, we can find how much heat is released.

When two moles of carbon are used,  are released. Two moles of carbon is equal to  of carbon, based on carbon's atomic mass.

Knowing this, we can set up proportions in order to determine how much heat is released by  of carbon.

So  of carbon results in  of heat being released to the surroundings.

Hess's law states that the enthalpy of the total reaction is equal to the enthalpy of the steps required to get to the total reaction, regardless of the path that is chosen. This means that we can combine the two half steps with known enthalpies in order to solve for the enthalpy of the main reaction.

Step 1.      

Step 2.    

Total:

Since step 1 results in two moles of liquid water, we need to use the second step twice in order to replace them with two moles of water vapor.

Combined:

Since the total reaction is created by step 1 occurring once and step 2 occurring twice, we can write the enthalpy as:

Use the given enthalpies of the steps to calculate the total change in enthalpy.

Use the following formula:

Plug in values:

Entropy is defined as the amount of disorder in a system and is favored in biological and chemical systems. Any system will prefer to have higher entropy, and spontaneous reactions will generally increase entropy in the system.

Gas particles move at higher velocity and with greater range than particles in liquids and solids. This contributes to their high level of entropy. Aqueous solutions gain entropy with the number of ions in solution, but do not reach the same level of entropy of gases. Colloids are homogenized mixtures, such as milk, and follow relatively the same principles as aqueous solutions.

Entropy can be thought of as the tendency for a system to favor disorder. This means that the least ordered scenario in a system is typically favored by probability. Entropy increases when disorder is increased. Examples include an ice cube melting into a puddle, a gas diffusing all throughout a room, and a mirror shattering. Each of these either increases the energy of the system or results in the creation of multiple pieces/particles from a single object.

When building a road, materials are placed in an ordered, specific manner. This gives it a negative entropy. 

Any reaction can be thought of as taking place in a system, while the surroundings are the rest of the universe. It helps to remember that the entropy of the universe is constantly increasing. This means that the entropy change in the universe increases following every reaction. A system can have a decrease in entropy, as long as the entropy of the surroundings increases by a greater value.