Chemistry · The first law of thermodynamics: Concept of work, heat, internal energy and enthalpy, heat capacity, molar heat capacity
The heat of combustion of \) at constant pressure and is What will be the heat o
The heat of combustion of \( \boldsymbol{H}_{2}(\boldsymbol{g}) \) at constant pressure and \( 300 K \) is \( -280 \mathrm{kJ} \) \( \operatorname{mol}^{-1} \) What will be the heat of combustion at constant volume and \( 300 K ? \)
- A. \( \Delta U=- \) -276.2587 k
- B. \( \Delta U=+276.2587 \mathrm{kJ} \)
- C. \( \Delta U=-27.63 \mathrm{kJ} \)
- D. None of these
Step-by-step solution
For the combustion of H2: H2(g) + 1/2 O2(g) → H2O(l). Δng = 0 - (1 + 0.5) = -1.5. Using ΔH = ΔU + Δng RT, we get ΔU = ΔH - Δng RT = -280 kJ mol⁻¹ - (-1.5 × 0.008314 kJ mol⁻¹ K⁻¹ × 300 K) = -280 + 3.7413 = -276.2587 kJ mol⁻¹.
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