Question

The caloriefic value $H_2\left(g\right)$ at STP is 12.78 kJ/L hence approximate standard enthalpy of formation of $H_{2}O\left(\ell \right)$ is –

• A. –143 kJ
• B. –286 kJ
• C. Zero
• D. +286 kJ

Answer 1

The correct option is B –286 kJ

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