Question

Ethanol undergoes combustion in oxygen to produce carbon dioxide gas and liquid water. The standard heat of combustion of ethanol, c2h5oh(l), is -1366.8 JK/mol. Given that [co2(g)] = -393.5kg/mol and [h20(l) = -285.8 KJ/ mol, what is the standard enthalpy of formation of ethanol?

Answer 1

Answer:

$-277.6\ \text{kJ/mol}$

Explanation:

Heat of combustion of $C_2H_5OH(l)$ = -1366.8 kJ/mol

Heat of formation of $CO_2(g)$ = -393.5 kJ/mol

Heat of formation of $H_2O(l)$ = -285.8 kJ/mol

The reaction is

$C_2H_5OH(l)\rightarrow 2CO_2(g)+3H_2O(l)$

Assuming $x$ is the standard enthalpy of formation of ethanol

$-1366.8=2\times (-393.5)+3\times (-285.8)-x\\\Rightarrow x=2\times (-393.5)+3\times (-285.8)+1366.8\\\Rightarrow x=-277.6\ \text{kJ/mol}$

The standard enthalpy of formation of ethanol is $-277.6\ \text{kJ/mol}$.