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.

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.

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.

A reaction will have a positive change in entropy when the disorder of the system is increasing. This can happen when a liquid transitions to a gas, or more gas molecules are formed in the reaction.

Since two molecules of gaseous nitrogen dioxide can combine to form one molecule of dinitrogen tetroxide, the amount of gaseous molecules is halved. This increases order, which decreases the entropy of the system.

Equilibrium is the basis of entropy, which can essentially be thought of as the distribution of energy in the system. For a reaction at a given temperature, the system's entropy will be at a maximum when it reaches equilbrium because this is the ideal energy state, and the forward and reverse reactions are occurring at a steady rate.

Since we have the entropies of formation, we can find the entropy of the reaction using the following equation:

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

Since this is the entropy for the reaction when two moles of ammonia are formed, we must divide this entropy by two in order to solve for the entropy of one mole.