Since we have the enthalpies of formation, we can find the enthalpy of the reaction using the following equation:

We will need to use the coefficients from the balanced equation to calculate the enthalpy.

Since oxygen gas is elemental, it does not have an enthalpy of formation, and is omitted from the equation.

This problem requires a knowledge of the energy involved when bonds are broken versus when bonds are formed.  Energy is released when bonds are formed, and energy is consumed when bonds are broken.  Here, methane is being formed from C and H_2.  Since the carbon source, graphite, is monoatomic the carbon will be involved only in the formation of C–H bonds on it's way to forming methane.  The H however exists as H₂ so bonds will need to be broken to allow for C–H bonds to form.  So first energy is consumed to break the H–H bonds, it is then released when the C–H bonds form.

When heat is added, enthalpy increases, ΔH refers to enthalpy

ΔS refers to entropy, which is disorder; disorder increases as it moves from solid to liquid to gas state.

As ice goes to liquid water, entropy increases

The change in enthalpy of a reaction is determined by the amount of heat gained when the products bonds form, versus the amount of heat lost to break the bonds in the reactants. The correct formula for the enthalpy of reaction is the difference between the enthalpy of the products and that of the reactants:

The reactions given show the heats of formation of all the reactants and products, and we know the heat of formation of  is zero because it is a pure element. Formation of the product,  gives us . For the reactants,  gives us  plus  for . Recall that the overall reaction's change in enthalpy is:

Thus for this overall reaction:

Of phases, from greatest to least entropy is gas>liquid>solid. Dissolving a salt into solution is an increase in entropy because the salt has greater space to move. The only decrease in entropy is condensation of water on glass (gas to liquid)

Entropy for phases are Gas>Liquid>Solid. A salt dissolving into solution has a positive entropy change (the solution becomes more chaotic). Therefore all of the listed reactions are a positive change in entropy, making E the correct answer.

Entropy can be thought of as the tendency for a system to become disordered, or random. Osmosis, melting ice, and a clean room becoming dirty are all examples of entropy at work. Each of these processes will occur spontaneously without the input of outside energy or work.

If you make a skyscraper, you are incorporating a series of compounds and building products into a single, distinct formation. Think of it this way: what are the odds that mother nature would spontaneously build a building? This process is very ordered, which means that entropy of the universe has decreased.

The change in entropy is calculated by:

When  cannot be measured, it can be calculated from known entropies of formation.

It is important to first balance the reaction before performing calculations. The coefficients are important in determining the change in entropy of a reaction.

The change in entropy is calculated by:

When  cannot be measured, it can be calculated from known entropies of formation.

It is important to first balance the reaction before performing calculations. The coefficients are important in determining the change in entropy of a reaction.