Energetics Equations

Question 1

Equation for total Change in entropy of a system

Answer 1

ΔS system = ΣΔS Products - ΣΔS reactants

Question 2

Equation for total change in entropy

Answer 2

ΔS total = ΔS system + ΔS surroundings

Question 3

Equation for change in entropy of surroundings

Answer 3

ΔS surroundings = -ΔΗ / Τ

-Where ΔH is the enthalpy change of the reaction
- Where T is temperature of reaction measured Kelvin

Question 4

Equation for change in Gibbs free energy

Answer 4

ΔG = ΔH - T(ΔS System)

Question 5

What must ΔG be for a reaction to be feasible

Answer 5

Negative (less than or equal to 0)

Question 6

What must ΔS be for a reaction to be feasible

Answer 6

Positive

Question 7

State the equation linking ΔG , K, T and R

Answer 7

ΔG = -RT lnK

-where R is the gas constant (8.31J /K /Mol)
- T is temperature in Kelvin (K)
- K is the equilibrium constant for a reaction
- Gibbs free energy is measured in Jmol-1 here because R is measured in J K-1mol-1

Question 8

Enthalpy of solution equation

Answer 8

Enthalpy of solution = (Hydration enthalpies of ions ) - Lattice enthalpy

Question 9

Enthalpy change of a reaction

Answer 9

Enthalpy change for breaking bonds - enthalpy change for making bonds

Question 10

What is the equation linking ΔG , Ecell , n and F

Answer 10

ΔG = -nFEcell

-where n is the number of electrons transferred in the redox reaction

-F is the faraday constant (given)

-E cell is the standard cell potential for the redox reaction AT STANDARD CONDITIONS