Question

Calculate the heat of hydrogenation of ethane 𝐶2𝐻4 using the following reactions:

2𝐶 (𝑔𝑟𝑎𝑝ℎ𝑖𝑡𝑒) + 3𝐻2 (𝑔) → 𝐶2𝐻6 (𝑔) ∆𝐻𝑓 = −84.5 𝑘𝐽/𝑚𝑜𝑙

2𝐶(𝑔𝑟𝑎𝑝ℎ𝑖𝑡𝑒) + 2𝐻2 (𝑔) → 𝐶2𝐻4 (𝑔) ∆𝐻𝑓 = 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$=$ $\Delta H_1-\Delta H_2$

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