Question

Predict the sign of delta S & calculate delta S for each:

a) 2H2S (g) + SO2 (g) --> 3Srhombic (s) + 2H2O (g)

I know the delta S is negative since we're going from a gas to a solid but I need help calculating the delta S. Please show all work.

b) 2SO3 (g) --> 2 SO2 (g) + O2 (g)

Delta S here would be positive but that's just a guess. Please confirm that and show how to obtain delta S.

c) Fe2O3 (s) + 3H2 (g) --> 2Fe (s) + 3H2O (g)

I think delta S would be negative since there are more moles of solid on the reacant side. Is that correct? And how do we get delta S.

Thank you!

Answer 1

a. The first reaction is going from 3 moles of gas( 2 moles of H2S and 1 mole of SO2) to 2 moles of gas (H2O vapour) and 3 moles of solid. Therefore, in this reaction, decreasing the number of moles of gas particles, so the entropy would decrease, giving a ΔS < 0.

b. Similarly the second reaction is from 2 moles of gas to 3, so ΔS would be positive.

c. In third reaction, the number of moles of gas is the same on both sides, but the total number of particles is increasing in the reaction so the ΔS would be positive.