Question

1. Calculate the heat of hydrogenation of ethane (C₂H₆) given the following thermochemical equations:

a. 2 C (graphite) + 3 H₂ (g) 🡺 C₂H₆ (g)      ΔH_f^o = - 84.5 kJ/mol

b. 2 C (graphite) + 2 H₂ (g) 🡺 C₂H₄ (g)      ΔH_f^o =   52.3 kJ/mol

Answer 1

Reaction of heat of hydrogenation of ethane:

$C_2H_4+H_2\Rightarrow C_2H_6$

Given that:

Equation .1.

$2C+3H_2\Rightarrow C_2H_6:\Delta H_1=-84.5KJ/mol$

Equation .2.

$2C+2H_2\Rightarrow C_2H_4:\Delta H_2=$ $52.3KJ/mol$

Now to form the main equation we have to subtract equation 2 from equation 1:

So heat of hydrogenation$=$ $\Delta H_1-\Delta H_2$

$=-84.5-52.3=-136.8KJ/mol$