Question

7. Consider the following balanced thermochemical equationfor a reaction sometimes used for H2S production:
⅛S8(s) + H2(g) → H2S(g) ∆Hrxn = -20.2 kJ
(a) Is this an exothermic or endothermic reaction?
(b) What is ∆Hrxn for the reverse reaction?
(c) What is ∆H when 3.2 mol of S8 reacts?
(d) What is ∆H when 20.0 g of S8 reacts?

Answer 1

1/8 S8 (s) + H2 (g) → H2S (g) ΔHrxn = -20.2 kJ

(a)Is this an exothermic or endothermic reaction?

As the ΔH is negative the reaction is exothermic.

(b)What is ΔHrxn for the reverse reaction?

 It would require +20.2kJ (ie you put it in) per mole of H2S to produce 1/8 S8 and H2

(c)What is ΔH when 3.2 mol of S8 react?

 In either case, assuming the stoichiometric relationships were maintained (ie H2 was also increased by a factor 3.2) then the enthalpy change would be multiplied by 3.2