Question

The equilibrium constant for the reaction

H₂(g) + S(s) ⇔H₂S(g) is 20.0 at 925K and 10.25 at 1000K, respectively. To calculate the standard enthalpy of the reaction.

Answer 1

This can be done by using formula from Vant Hoff eqation, from which we an write

log(k2\k1) = ($\Delta$H\2.303xR)x(1\T₁ - 1\T₂)where k2 = 10.25 , k1 = 20.0 , T₁ = 925 K , T₂ = 1000k , R = 8.314 J mol^-1K^-1

$\Delta$H = standard enthalpy chnage

or, log(10.25\20.0)= log(0.5125) = -0.29 = ($\Delta$H\2.303xR)x(1\T₁ - 1\T₂)

-0.29x2.303x8.314 Jmol^-1k^-1 = $\Delta$H x (1\925 - 1\1000) K^-1

or, 5.55 Jmol-1 = $\Delta$H x (0.00108 - 0.001) = $\Delta$H x 8 x 10^-5

or , $\Delta H = (5.55$\8)x10⁵ Jmol^-1 = 69375 Jmol^-1 = 69.375 kJ mol^-1 (ans)