Question

The calorific value of $H_2\left(g\right)$ at STP is $12.78kJ/L$. Find the approximate standard enthalpy of formation of $H_{2}O\left(l\right)$.

• A. $-143kJ$
• B. $-286kJ$
• C. Zero
• D. $+286kJ$

Answer 1

The correct option is B $-286kJ$

$1L{H}_2\left(g\right)atSTP=\frac{1}{22.4}mol$
$\therefore$ Heat released due to combustion of $\frac{1}{22.4}$ mol of $H_2\left(g\right)=12.78kJ$
Heat released due to combustion of 1 mol of $H_2\left(g\right)$
$=12.78\times 22.4=286.27kJ$
$\therefore$ standard enthalpy of formation of $H_{2}O\left(l\right)=-286kJ$