Question

Using the table given below, determine the heat of combustion of one mole of $C_2{H}_4$ at 298 K and 1 atm?

Compound	$\Delta$ of formation (kcal/mol)
$H_{2}O\left(g\right)$	-57.8
$C_2{H}_6\left(g\right)$	-20/2
$C_2{H}_4\left(g\right)$	12.5
$C_2{H}_2\left(g\right)$	54.2
$CO\left(g\right)$	-26.4
${CO}_2\left(g\right)$	-94.1

• A. 316.3 kcal
• B. 12.5 kcal
• C. -291.3 kcal
• D. -316.3 kcal
• E. 57.8 kcal

Answer 1

Answer: (D)

-316.3 kcal

The combustion reaction is shown below.

$C_2{H}_4+3O_2\to 2C{O}_2+2H_{2}O$

$\Delta H_{\text{combustion}}=2\Delta H_{f,C{O}_2}+2\Delta H_{f,H_{2}O}-\Delta H_{f,C_2{H}_4}-3\Delta H_{f,O_2}$
$\Delta H_{\text{combustion}}=2(-\text{94.1})+2(-57.8)-12.5-3\left(0\right)$
$\Delta H_{\text{combustion}}=-\text{316.3 kcal/mol}$