Question

For which of the following reactions is ΔS° < 0 at 25°C?

Question 14 options:

	2KClO3(s) → 2KCl(s) + 3O2(g)
	2HgO(s) → 2Hg(l) + O2(g)
	Br2(l) → Br2(g)
	P4(s) + 5O2(g) → P4O10(s)
	(NH4)2Cr2O7(s) → N2(g) + 4H2O(l) + Cr2O3(s) For which of the following reactions is ΔS° > 0 at 25°C? Question 15 options: MgO(s) + CO2(g) → MgCO3(s) 2H2(g) + O2(l) → 2H2O(l) 2Li(s) + O2(g) → Li2O(s) 2CO(g) + O2(g) → 2CO2(g) F3BNH3(s) → BF3(g) + NH3(g) Consider the following reaction, which is spontaneous at room temperature. NH3(g) + BF3(g) → H3NBF3(s) One would predict that Question 16 options: ΔG is negative at all temperatures. ΔH is positive and ΔS is negative for the reaction. ΔH is negative and ΔS is positive for the reaction. ΔH is positive and ΔS is positive for the reaction. ΔH is negative and ΔS is negative for the reaction

Answer 1

14) ΔS° < 0 means in the forward reaction, entropy decreases.

P₄(s) + 5O₂(g) → P₄O₁₀(s)..................(answer)

In this reaction, 5 mole gaseous reactant produce solid product.

so entropy decreases.

15) ΔS° > 0 means in the forward reaction, entropy increases.

F₃BNH₃(s) → BF₃(g) + NH₃(g)..................(answer)

In this reaction solid product produce gaseous products and hence entropy increases.

16)

NH₃(g) + BF₃(g) → H₃NBF₃(s)

In this reaction, entropy decreases. that is delta S = (-)ve.

As in this reaction bond formation occurs and hence this is exothermic reaction and delta H = (-)ve.

ΔH is negative and ΔS is negative for the reaction