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Enthalpy of formation of methane from enthalpies of combustion

The same question, asked 2 times: 20 Apr 2026 S2*, 12 May 2026 S1. Every wording below, oldest first.

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  1. Question 1

    20 Apr 2026 S2

    5
    The enthalpy of combustion of C, H2\mathrm{H_2}, and CH4\mathrm{CH_4} are −390-390, −285-285 and −890-890 kJ/mol. Find the enthalpy of formation of methane.

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  2. Question 2

    12 May 2026 S1

    7
    Calculate ΔfH\Delta_f H for C(s)+2H2(g)→CH4(g)\mathrm{C(s) + 2H_2(g) \rightarrow CH_4(g)} i. C(s)+O2(g)→CO2(g)\mathrm{C(s) + O_2(g) \rightarrow CO_2(g)}; ΔH1=−393.5\Delta H_1 = -393.5 kJ/mol ii. H2(g)+1/2 O2(g)→H2O(l)\mathrm{H_2(g) + 1/2\,O_2(g) \rightarrow H_2O(l)}; ΔH2=−285.8\Delta H_2 = -285.8 kJ/mol iii. CH4(g)+2O2(g)→CO2(g)+2H2O(l)\mathrm{CH_4(g) + 2O_2(g) \rightarrow CO_2(g) + 2H_2O(l)}; ΔH3=−890.3\Delta H_3 = -890.3 kJ/mol

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