Question

Consider the decomposition of solid ammonium chloride to ammonia andhydrogen chloride gases. What do you predict for the sign of deltaS°? Consider a particulate-level explanation for your prediction. Calculate the value of delta S° for thereaction, and compare it to your prediction. Now consider the decomposition of aqueous ammonium chloride to aqueous ammonia and hydrochloric acid. What doyou predict for the sign of deltaS°? Why? Compare your prediction to the calculated value.

Answer 1

Consider the decomposition of solid ammonium chloride to ammonia andhydrogen chloride gases.

NH4Cl(s) = NH3(g) + HCl(g)

What do you predict for the sign of deltaS°?

the entropy mus incerase, since solid is much more stable than the gases. Note that there is plenty of moles of gas creation, which increase disorder, dS = positive

Consider a particulate-level explanation for your prediction.

in the moelcular level, there are now much more microstates possible, therefore S = k*ln(K)

if K increases, then S entrpoy inctreases

Calculate the value of delta S° for thereaction, and compare it to your prediction.

dS = HCl + NH3 - NH4Cl

dS = 186.9 + 192.8 - 94.6 = 285.1 J/K

as stated, it increases

Now consider the decomposition of aqueous ammonium chloride to aqueous ammonia and hydrochloric acid.

NH4Cl(aq) = NH3(aq) + HCl(aq)

What doyou predict for the sign of deltaS°?

Entropy increases, since aqueous is much more favoured state than solids. Solids will decrease the entropy of the system compared to ions

Why?

because solid is very ordered system, compared to ionic chaotic solution