Thermodynamics and Free Energy: Concepts, Calculations, and Spontaneity

What is the definition of reaction in thermodynamics?

The reaction is defined by subtracting the sum of the standard entropies of the reactants multiplied by their stoichiometric coefficients from the sum of the standard entropies of the products multiplied by their stoichiometric coefficients.

What does the third law of thermodynamics state about entropy?

It establishes that the entropy of a perfect crystal at absolute zero is zero.

What factors affect the entropy of a substance at a given temperature?

The state, size, and molecular complexity of the substance.

How can ΔG (Gibbs Free Energy change) be calculated?

ΔG can be calculated from ΔH and ΔS°, from free energies of formation (only at 25 °C), or from the ΔG's of reactions that sum to the reaction of interest.

What does a negative ΔG indicate?

It represents the theoretical amount of energy available to do work. A negative ΔG indicates that a reaction is spontaneous under standard conditions.

What does a positive ΔG indicate?

It represents the minimum amount of energy required to make a nonspontaneous process occur. A positive ΔG indicates that the reaction is nonspontaneous.

What is the equation for ΔG under nonstandard conditions?

ΔG = ΔG° + RT ln Q.

How is ΔG related to the equilibrium constant (K)?

Under standard conditions, ΔG is directly proportional to the negative of the natural log of the equilibrium constant, K.

What is the equation for the temperature dependence of ΔG?

ΔG° = ΔH° - TΔS.

What is the definition of entropy (S)?

Entropy is a measure of energy dispersal per unit temperature and is proportional to the number of energetically equivalent ways in which the components of a system can be arranged.

What happens to entropy when a substance changes state from solid to liquid?

The entropy of the substance increases.

What is the relationship between the change in entropy of the surroundings and the change in enthalpy of the system?

The change in entropy of the surroundings increases when the change in enthalpy of the system (ΔHsys) is negative (i.e., for exothermic reactions).

What is Gibbs Free Energy (G)?

Gibbs Free Energy is a thermodynamic function that is proportional to the negative of the change in the entropy of the universe.

What is the equation for the change in entropy (ΔS)?

ΔS = Sfinal - Sintial.

What is the equation for calculating the standard change in entropy for a reaction?

ΔS°rxn = ΣnpS°(products) - ΣnsS°(reactants).

What is the equation for calculating ΔG from ΔH and ΔS?

ΔG = ΔH - TΔS.

What is the significance of the second law of thermodynamics?

It states that for any spontaneous process, the entropy of the universe increases.

What is the relationship between spontaneity and temperature in thermodynamics?

At low temperatures, reactions with positive ΔH and positive ΔS are nonspontaneous, while at high temperatures, reactions with positive ΔH and positive ΔS can become spontaneous.

What is the value of the gas constant (R) in J/mol K?

R = 8.314 J/mol K.

What is the equation for the change in entropy of the surroundings (ΔSsurr)?

ΔSsurr = -ΔHsys / T (at constant T, P).