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Enthalpy of a reaction from standard enthalpies of formation

This type of question, asked 4 times: 11 Apr 2023, 30 Jan 2024, 5 Apr 2024, 8 Apr 2026 S2. All 4 questions below, oldest first.

Try each one first, then open its answer.

  1. Question 1

    11 Apr 2023

    56
    Solid fuel used in rocket is a mixture of Fe2O3Fe_{2}O_{3} and AlAl (in ratio 1:21:2 ). The heat evolved (kJ)(kJ) per gram of the mixture is___ (Nearest integer) Given: ΔHfθ(Al2O3)=−1700 kJ mol−1\Delta H_{f}^{\theta}\left( Al_{2}O_{3} \right)= - 1700\text{ }kJ{\text{ }mol}^{- 1}
    ΔHf⊖(Fe2O3)=−840 kJ mol−1\Delta H_{f}^{\ominus}\left( Fe_{2}O_{3} \right)= - 840\text{ }kJ{\text{ }mol}^{- 1}
    Molar mass of Fe,AlFe,Al and OO are 56,27 and 16 g16\text{ }g mol−1mol^{- 1} respectively.

  2. Question 2

    30 Jan 2024

    143
    Two reactions are given below:
    2Fe(s)+32O2( g)→Fe2O3( s),ΔHo=−822 kJ/molC(s)+12O2( g)→CO(g),ΔHo=−110 kJ/mol\begin{matrix} & 2Fe_{(s)}+\frac{3}{2}O_{2(\text{ }g)}\rightarrow Fe_{2}O_{3(\text{ }s)},\Delta H^{o}= - 822\text{ }kJ/mol \\ & C_{(s)}+\frac{1}{2}O_{2(\text{ }g)}\rightarrow CO_{(g)},\Delta H^{o}= - 110\text{ }kJ/mol \end{matrix}
    Then enthalpy change for following reaction 3C(s)+Fe2O3( s)→2Fe(s)+3CO(g)3C_{(s)}+Fe_{2}O_{3(\text{ }s)}\rightarrow 2Fe_{(s)}+ 3CO_{(g)}

  3. Question 3

    5 Apr 2024

    141
    Combustion of 1 mole of benzene is expressed at C6H6(l)+152O2( g)→6CO2( g)+3H2O(l)C_{6}H_{6}(l) +\frac{15}{2}O_{2}(\text{ }g) \rightarrow 6CO_{2}(\text{ }g) + 3H_{2}O(l). The standard enthalpy of combustion of 2 mol of benzene is - ' xx ' kJ. x=x = _______ . (1) standard Enthalpy of formation of 1 mol1\text{ }mol of C6H6(l)C_{6}H_{6}(l), for the reaction 6C6C (graphite) +3H2( g)→C6H6(l)+ 3H_{2}(\text{ }g) \rightarrow C_{6}H_{6}(l) is 48.5 kJ mol−148.5\text{ }kJ{\text{ }mol}^{- 1}. (2) Standard Enthalpy of formation of 1 mol1\text{ }mol of CO2( g)CO_{2}(\text{ }g), for the reaction CC (graphite) +O2(g)→CO2( g)+O_{2(g)}\rightarrow CO_{2}(\text{ }g) is −393.5 kJ mol−1- 393.5\text{ }kJ{\text{ }mol}^{- 1}. (3) Standard and Enthalpy of formation of 1 mol of H2O(l)H_{2}O(l), for the reaction
    H2( g)+12O2( g)→H2O(l) is −286 kJ mol−1H_{2}(\text{ }g) +\frac{1}{2}O_{2}(\text{ }g) \rightarrow H_{2}O(l)\text{~is~}- 286\text{ }kJ{\text{ }mol}^{- 1}

  4. Question 4

    8 Apr 2026 S2

    49
    Consider the reaction :
    2H2 S( g)+3O2( g)→2H2O(l)+2SO2( g)2H_{2}\text{ }S(\text{ }g) + 3O_{2}(\text{ }g) \rightarrow 2H_{2}O(l) + 2{SO}_{2}(\text{ }g)
    The magnitude of enthalpy change for the reaction in kJmol−1kJ{mol}^{- 1} is ____\_\_\_\_ . (Nearest integer) Given : ΔfH⊖(H2 S)=−20.1 kJ mol−1\Delta_{f}H^{\ominus}\left( H_{2}\text{ }S \right) = - 20.1\text{ }kJ{\text{ }mol}^{- 1}
    ΔfHΘ(H2O)=−286.0 kJ mol−1\Delta_{f}H^{\Theta}\left( H_{2}O \right) = - 286.0\text{ }kJ{\text{ }mol}^{- 1}
    ΔfHΘ(SO2)=−297.0 kJ mol−1\Delta_{f}H^{\Theta}\left( {SO}_{2} \right) = - 297.0\text{ }kJ{\text{ }mol}^{- 1}