Chemical Thermodynamics Overview.

 

Chemical thermodynamics deals with the study of energy changes and the direction of chemical reactions. Here are some key concepts related to spontaneous processes, entropy, Gibbs free energy, and equilibrium constants:

1. Spontaneous Process and Entropy:

A spontaneous process is a reaction or a physical change that occurs without any external influence. In other words, it proceeds on its own without needing additional energy input. Entropy (S) is a thermodynamic quantity that measures the degree of disorder or randomness in a system. The second law of thermodynamics states that the entropy of an isolated system always increases in a spontaneous process.

2. Entropy Change for a Phase Transition:

When a substance undergoes a phase transition, such as from solid to liquid (melting) or from liquid to gas (vaporization), there is a change in entropy. For most phase transitions, the entropy increases because the molecules or particles have more freedom of movement in the higher energy phase, resulting in greater disorder.

3. Entropy Change for a Reaction:

The entropy change (ΔS) for a chemical reaction is the difference between the entropy of the products and the entropy of the reactants. It is given by:

ΔS = ΣS(products) - ΣS(reactants)

If the entropy change is positive (ΔS > 0), the reaction increases the disorder of the system and is favored to be spontaneous at higher temperatures.

4. Gibbs Free Energy and Direction of Chemical Reaction:

Gibbs free energy (G) is a thermodynamic potential that combines both enthalpy (H) and entropy (S) to predict whether a chemical reaction is spontaneous under a given set of conditions (temperature and pressure). It is defined as:

ΔG = ΔH - TΔS

where ΔH is the enthalpy change and TΔS is the temperature multiplied by the entropy change. A negative ΔG indicates a spontaneous reaction, while a positive ΔG indicates a non-spontaneous reaction.

5. Standard Free Energy Change and Equilibrium Constant:

The standard free energy change (ΔG°) is the Gibbs free energy change for a reaction under standard conditions, which includes a temperature of 298 K (25°C), a pressure of 1 atm, and all reactants and products at their standard states. The relationship between ΔG° and the equilibrium constant (K) is given by the equation:

ΔG° = -RT ln(K)

where R is the gas constant (8.314 J/(mol·K)), T is the temperature in Kelvin, and ln denotes the natural logarithm. If ΔG° is negative, the equilibrium constant K is greater than 1, indicating that the reaction favors the formation of products at equilibrium.

In summary, understanding the spontaneity of processes, entropy changes, Gibbs free energy, and equilibrium constants is essential in predicting the direction and feasibility of chemical reactions under various conditions.