Question

Which variable is not required to calculate the gibbs free-energy change for a chemical reaction? temperature in kelvins change in entropy change in enthalpy temperature in °c?

Answer 1

the answer:
Temperature in °C is not required

As Gibbs free energy change formula is:

Δ G = ΔH -TΔS

when ΔH is enthalpy change
and T is the temperature in Kelvin
and ΔS is Entropy change 
So the only factor that not required to measure ΔG is T in °C

Answer 2

Gibbs free energy change equation is as follows;
ΔG = ΔH - TΔS
where ΔG - change in Gibbs energy which decides whether a reaction is spontaneous or not spontaneous 
ΔH - change in enthalpy 
T - temperature 
ΔS - change in entropy 
entropy units are J/K , enthalpy and gibbs free energy units are in kJ. Product of entropy and temperature should be in unit Joules. As entropy is J/K, temperature should be in Kelvin as to give product as Joules.
Therefore variable that is not required is temperature in Celsius. If temperature is in celsius it needs to be converted to Kelvin before entering in the gibbs energy equation.