Question

Which of the following conditions will result in a reaction that is spontaneous only at high temperatures?

negative enthalpy change and negative entropy change
negative enthalpy change and positive entropy change
positive enthalpy change and negative entropy change
positive enthalpy change and positive entropy change

Answer 1

You have to use the equation ΔG=ΔH-TΔS.
With that equation you know that a reaction with a positive change in enthalpy and positive change in entropy will only be spontaneous at high temperatures since ΔG needs to be negative for a reaction to be spontaneous.

I hopet this helps. Let me know if anything is unclear.