Question

The standard heats of formation, delta Hf, fro C2H4 is +52.3KJ/mole. If C2H4 (ethylene) reacts with H2 to produce C2H6 (ethane) according to the following equation:

C2H4+H2=C2H6 deltaH=-137KJ

What is the heat of formation of C2H6?

Answer 1

Gives

$C_2H_2+H_2\rightarrow C_2H_6$

$∆H=∆H_{rec}-∆H_{pro}$

$$∆H_{rec}=(52.3-0)kJ/mol=52.3KJ/mol$$

$∆H_{pro}=?$

$∆H_{c_2H_6}=?$

$∆H=-137kJ$

$∆H_{c_2H_6}=∆H_{rec}-∆H$

$$∆H_{c_2H_6}=(52.3kJ/mol)\times1mol-(-137)=189.3kJ$$