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Calorimetry

The heat of c...

Question

The heat of combustion of gaseous methane $({C H}_{4})$ at constant volume is measured in a bomb calorimeter at 298 K and is found to be $- 885.4 k J {m o l}^{- 1}$ . Find the value of enthalpy change.

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Solution

Combustion of $C H_{4}$ -
${C H_{4}}_{(g)} + 2 {O_{2}}_{(g)} ⟶ {C O_{2}}_{(g)} + 2 {H_{2} O}_{(l)}$
$Δ n_{g} = n_{P} - n_{R} = 1 - (2 + 1) = - 2$
Given:- $Δ U = - 885.4 k J / m o l$
$T = 298 K$
As we know that,
$Δ H = Δ U + Δ n_{g} R T$
$\Rightarrow Δ H = - 885.4 + (- 2 \times 8.314 \times 10^{- 3} \times 298)$
$\Rightarrow Δ H = - 885.4 - 4.95 = - 890.05 k J / m o l$
Hence the value of enthalpy change is $- 890.05 k J / m o l$ .

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