Question

Iron undergoes two solid-solid transitions as it is heated from 298 K to 1800 K. Given delta H^o = 0.900 kJ mol^-1 at 1184 K for the a - g transition delta H^o = 0.837 kJ mol^-1 at 1665 K for a g - d transition, calculate delta S^o_system for each change. Comment on the changes in randomness

Answer 1

Delta G = Delta H - TDelta S.

During a phase transition, Delta G = 0, so substituting and rearranging gives:

Delta H = T Delta S

we know Delta H and the temperature, just substitute and solve for Delta S.

Delta S=Delta H / T=0.9/1184= 7.60*10^-4 KJ/K

also  Delta S=Delta H / T=0.837/1665= 5.027*10^-4 KJ/K

All we need to know is that entropy change (delta S) is the change in the amount of disorder between reactants and products; entropy is positive which means that the products are more disordered than the reactants.