Exothermic and endothermic reactions

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Question 9
Medium

Methane burns in oxygen to produce carbon dioxide and water according to the following chemical equation:

CH4+2O2⟶CO2+2H2O\text{CH}_4 + 2\text{O}_2 \longrightarrow \text{CO}_2 + 2 \text{H}_2\text{O}CH4​+2O2​⟶CO2​+2H2​O

The bonds broken and made during this reaction are as follows:

  • Reactants: one mole of CH4\text{CH}_4CH4​ contains 4 moles of C−H\text{C}-\text{H}C−H bonds; two moles of O2\text{O}_2O2​ contain 2 moles of O=O\text{O}=\text{O}O=O bonds.
  • Products: one mole of CO2\text{CO}_2CO2​ contains 2 moles of C=O\text{C}=\text{O}C=O bonds; two moles of H2O\text{H}_2\text{O}H2​O contain 4 moles of O−H\text{O}-\text{H}O−H bonds.

Table 1 shows the bond energies for these bonds.

Table 1

BondBond energy (kJ/mol)
C−H\text{C}-\text{H}C−H413
O=O\text{O}=\text{O}O=O495
C=O\text{C}=\text{O}C=O799
O−H\text{O}-\text{H}O−H463
a.

Calculate the overall energy change for the reaction using the bond energies in Table 1.

[3]
b.

Explain why this reaction is exothermic, using values from your calculation.

[2]

Exothermic and endothermic reactions Questions

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  3. /Exothermic and endothermic reactions