Question

What is the Gibbs free energy change (ΔG) for the reaction, given the standard Gibbs free energy change (ΔG°) and the reaction quotient (Q)? For example, for the reaction A + B → C, if ΔG° is -100 kJ/mol and Q is 0.5, what is the ΔG for the reaction?

Answer 1

To calculate the Gibbs free energy change  G  for a reaction, you can use the following equation:G = G + RT ln Q where G is the standard Gibbs free energy change, R is the gas constant  8.314 J/molK , T is the temperature in Kelvin, and Q is the reaction quotient.In this example, G is -100 kJ/mol, which is equal to -100,000 J/mol, and Q is 0.5. We'll assume the temperature is 298 K  25C , which is a common reference temperature for standard conditions.Now, plug in the values into the equation:G = -100,000 J/mol +  8.314 J/molK  298 K  ln 0.5 G = -100,000 J/mol +  8.314 J/molK  298 K   -0.693 G = -100,000 J/mol - 1716.4 J/molG  -101,716.4 J/molSo, the Gibbs free energy change  G  for the reaction is approximately -101,716.4 J/mol or -101.7 kJ/mol.