Which of the following circumstances will result in a reaction that is spontaneous only at high temperatures? a. positive enthalpy change and positive entropy change b. negative enthalpy change and negative entropy change c. positive enthalpy change and negative entropy change d. negative enthalpy change and positive entropy change

A. positive enthalpy change and positive entropy change

Explanation:

According to Gibb's equation:

= Gibbs free energy  

= enthalpy change

= entropy change  

T = temperature in Kelvin

= +ve, reaction is non spontaneous

= -ve, reaction is spontaneous

= 0, reaction is in equilibrium

Thus when = +ve

= +ve

  only when is higher which is possible at high temperatures

Reaction is spontaneous at high temperatures when positive enthalpy change and positive entropy change is there.

"standard molar enthalpy:

h2o ( liquid water ) : - 285.8 kj/mole

h2o ( water vapor ) : - 241.8 kj / mole.

δhrxn = - 241. 8 - ( - 285.8 )= -241.8 + 285.8 = 44.0

answer: 44.0 kj"