If a reaction has a △H of -120.0 kJ/mole and is spontaneous for all temperatures less than 200.0 K, what is it’s △S?

Answer 1

A spontaneous reaction is must have △G < 0, meaning that the change in free energy must be negative for the reaction to occur spontaneously.

For this problem, we will want to apply the formula, △G=△H-T△S, where △G is the change in free energy in joules per mole, △H is the change in enthalpy in joules per mole, T is the temperature in Kelvin, and △S is the change in entropy.

Solving the equation for △S yields

△S = (△H-△G) /T

If we want to solve the equation for when the reaction is spontaneous, we need to set △G =0.

Since the equation requires that we use △H in units of joules, we need to multiply the number of kilojoules by 1000 to find the value in joules.

Then, we can plug in the values for △H and T to obtain,

△S=( -120*1000 J/mol)/ *(200.0 K)= -600 J/(mol*K)