How much heat is released during the combustion of methane using the given bond dissociation energies:
CH₄ + 2 O₂ → CO₂ + 2H₂O
Number and types of bonds in each molecule:
CH₄ (4 C-H bonds) ;O₂ (1 O=O) ; (2 C=O bonds) ; (2 O-H bonds) .
Bond dissociation energies:
C-C (347 kJ/mol) ;C-H (413 kJ/mol) ;O=O (498 kJ/mol;C=O (799 kJ/mol) ;O-H (467 kJ/mol)

Question

Quizplus · Accepted Answer

First, we need to calculate the total energy required to break the bonds in the reactants:
4 C-H bonds * 413 kJ/mol = 1652 kJ/mol
1 O=O bond * 498 kJ/mol = 498 kJ/mol
2 C=O bonds * 799 kJ/mol = 1598 kJ/mol
2 O-H bonds * 467 kJ/mol = 934 kJ/mol

Total energy required = 4682 kJ/mol

Next, we need to calculate the total energy released when the new bonds form in the products:
1 C=O bond * 799 kJ/mol = 799 kJ/mol
2 O-H bonds * 467 kJ/mol = 934 kJ/mol

Total energy released = 1733 kJ/mol

Finally, we can calculate the overall heat released or absorbed by subtracting the energy required from the energy released:
1733 kJ/mol - 4682 kJ/mol = -2949 kJ/mol

However, this is not the final answer because we need to consider the coefficients in the balanced equation. The coefficients tell us how many moles of each substance are involved in the reaction. In this case, the coefficient for methane is 1 and for oxygen is 2. This means that we need twice as many moles of oxygen as methane in order to react completely.

To calculate the heat released per mole of methane, we need to divide the overall heat by the number of moles of methane:
-2949 kJ/mol / 1 mol = -2949 kJ/mol

Finally, we need to convert this to the correct units (kJ vs. J) and round to the correct number of significant figures:
-2949 kJ/mol * 1000 J/kJ = -2,949,000 J/mol ≈ -2.95 × 10^6 J/mol

This value is negative, which means that the reaction is exothermic (heat is released). The magnitude of the value is very large, indicating that a significant amount of heat is released during the reaction. The closest answer choice is B, which is -8181 kJ.

How Much Heat Is Released During the Combustion of Methane