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1. Butane [tex]\(C_4H_{10}(g)\left(\Delta H_f = -125.6 \, \text{kJ/mol}\right)\)[/tex] combusts in the presence of oxygen to form [tex]\(CO_2(g)\left(\Delta H_f = -393.5 \, \text{kJ/mol}\right)\)[/tex] and [tex]\(H_2O(g)\left(\Delta H_f = -241.82 \, \text{kJ/mol}\right)\)[/tex] in the reaction:

[tex]\[
2C_4H_{10}(g) + 13O_2(g) \rightarrow 8CO_2(g) + 10H_2O(g)
\][/tex]

What is the enthalpy of combustion, per mole, of butane?

Use [tex]\(\Delta H_{\text{rxn}} = \sum \left( \Delta H_{\text{f, products}} \right) - \sum \left( \Delta H_{\text{f, reactants}} \right)\)[/tex].

A. [tex]\(-5,315 \, \text{kJ/mol}\)[/tex]
B. [tex]\(-2,657.5 \, \text{kJ/mol}\)[/tex]
C. [tex]\(2,657.4 \, \text{kJ/mol}\)[/tex]
D. [tex]\(5,314.8 \, \text{kJ/mol}\)[/tex]

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Sagot :

To determine the enthalpy of combustion per mole of butane, we need to follow a few steps.

1. Identify the chemical reaction:
The balanced combustion reaction of butane is:
[tex]\[ 2 \, \text{C}_4\text{H}_{10} (g) + 13 \, \text{O}_2 (g) \rightarrow 8 \, \text{CO}_2 (g) + 10 \, \text{H}_2\text{O} (g) \][/tex]

2. Identify the given enthalpies of formation:
[tex]\[ \Delta H_{f, \text{C}_4\text{H}_{10}} = -125.6 \, \text{kJ/mol} \][/tex]
[tex]\[ \Delta H_{f, \text{CO}_2} = -393.5 \, \text{kJ/mol} \][/tex]
[tex]\[ \Delta H_{f, \text{H}_2\text{O}} = -241.82 \, \text{kJ/mol} \][/tex]

3. Calculate the sum of enthalpies of formation for the products:
[tex]\[ \sum \Delta H_{f, \text{products}} = 8 \times \Delta H_{f, \text{CO}_2} + 10 \times \Delta H_{f, \text{H}_2\text{O}} \][/tex]
Plugging in the values:
[tex]\[ \sum \Delta H_{f, \text{products}} = 8 \times (-393.5) + 10 \times (-241.82) = -3148 + (-2418.2) = -5566.2 \, \text{kJ} \][/tex]

4. Calculate the sum of enthalpies of formation for the reactants:
[tex]\[ \sum \Delta H_{f, \text{reactants}} = 2 \times \Delta H_{f, \text{C}_4\text{H}_{10}} \][/tex]
Plugging in the values:
[tex]\[ \sum \Delta H_{f, \text{reactants}} = 2 \times (-125.6) = -251.2 \, \text{kJ} \][/tex]

5. Calculate the enthalpy change of the reaction:
[tex]\[ \Delta H_{\text{rxn}} = \sum \Delta H_{f, \text{products}} - \sum \Delta H_{f, \text{reactants}} \][/tex]
Plugging in the values:
[tex]\[ \Delta H_{\text{rxn}} = -5566.2 - (-251.2) = -5566.2 + 251.2 = -5315.0 \, \text{kJ} \][/tex]

6. Determine the enthalpy of combustion per mole of butane:
Since the reaction involves 2 moles of C[tex]\(_4\)[/tex]H[tex]\(_{10}\)[/tex], we need to divide the total enthalpy change by 2:
[tex]\[ \Delta H_{\text{combustion per mole}} = \frac{\Delta H_{\text{rxn}}}{2} = \frac{-5315.0}{2} = -2657.5 \, \text{kJ/mol} \][/tex]

Thus, the enthalpy of combustion per mole of butane is [tex]\(\boxed{-2657.5 \, \text{kJ/mol}}\)[/tex].
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