The enthalpy of formation of methane at constant pressure and $300 K$ is $- 75.83 k J$ . What will be the heat of formation at constant volume? $(R = 8.3 J K^{- 1} {m o l}^{- 1})$

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Solution

The equation for the formation of methane is
$C (s) + 2 H_{2} 1 m o l e = C H_{4} 1 m o l e (g); Δ H = - 75.83 k J$
$Δ n = (1 - 2) = - 1$
Given, $Δ H = - 75.83 k J, R = 8.3 \times 10^{- 3} J K^{- 1} {m o l}^{- 1}, T = 300 K$
Applying $Δ H = Δ U + Δ n R T$
$- 75.83 = Δ U + (- 1) (8 \times 10^{- 3}) (300)$
So, $Δ U = - 75.83 + 2.49 = - 73.34 k J$

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The enthalpy of formation of methane at constant pressure and 300 K is −75.83 kJ. What will be the heat of formation at constant volume? (R=8.3JK−1mol−1)

The equation for the formation of methane isC(s)+2H21mole=CH41mole(g);ΔH=−75.83kJΔn=(1−2)=−1Given, ΔH=−75.83kJ,R=8.3×10−3JK−1mol−1,T=300KApplying ΔH=ΔU+ΔnRT−75.83=ΔU+(−1)(8×10−3)(300)So,ΔU=−75.83+2.49=−73.34kJ

The enthalpy of formation of methane at constant pressure and $300 K$ is $- 75.83 k J$ . What will be the heat of formation at constant volume? $(R = 8.3 J K^{- 1} {m o l}^{- 1})$