Entropy, Spontaneity and Free Energy Chapter 19 Entropy, Spontaneity and Free Energy

First Law of Thermodynamics Law of Conservation of Energy. This law suggests that energy can be transferred from one system to another in many forms. However, it can not be created nor destroyed. Thus, the total amount of energy available in the Universe is constant.

This is also evident in Enthalpy Rxns Cdiamond + O2(g) CO2(g) ΔH = -396 kj CO2(g)  Cdiamond + O2(g) ΔH= +396 kj What are the forms of Energy?

First Law of Thermodynamics The first law is all about the accounting of energy. How much energy is involved in the change? Does the energy flow in or out of a system? What form does the energy finally assume?

Spontaneous Processes A process that will occur without any energy input from the surroundings. A process that will occur on its own. Thermodynamics considers only the initial and final states of a reaction and not the pathway.

Spontaneous does not mean fast!

Spontaneous reactions: these reactions never occur in the reverse. Heat moves from warm object to cold. Wood burns in an exothermic reaction. Below 0 ° water freezes; above 0 ° water melts.

Spontaneous movement of gases

Entropy

Entropy symbol: S The driving force for a spontaneous reaction is an increase in entropy in the universe. Entropy is randomness, or the measure of molecular disorder.

Entropy is the associated with probability Nature proceeds spontaneously towards the states that have the highest probability of existing. So… which arrangement is most likely to occur?

Probability

1 2 3 4 5

Probability The probability is that in an arrangement of 4 molecules and two places that arrangement 3 is the most likely. The likelihood of all 4 in one chamber is low.

Probability of finding all gas molecules in left bulb as a function of the total number of gas particles # molecules Probability 1 ½ 2 ½ x ½ = ¼ 3 ½ x ½ x ½ = 1/(2)3 5 ½ x ½ x ½ x ½ x ½ = 1/(2)5 n ½ x ½ x ½ x…1/(2)n