Question

When 2.50 g of methane burns in oxygen, 125 kJ of heat is produced. The molar mass of CH₄ is 16.04 g/mol. What is the enthalpy of combustion per mole of methane under these conditions?

a) -312.5 kJ/mol
b) -125 kJ/mol
c) -50 kJ/mol
d) -20 kJ/mol

Answer 1

The enthalpy of combustion per mole of methane is calculated to be -802.3 kJ/mol by converting the given mass of methane to moles and relating it to the heat produced. However, this result does not match the available answer choices, suggesting an error in the provided options.

Step-by-step explanation:

When 2.50 g of methane burns in oxygen, 125 kJ of heat is produced, and to find the enthalpy of combustion per mole of methane, we must first convert grams to moles using methane's molar mass. This is calculated as follows:

2.50 g CH₄ × (1 mol CH₄ / 16.04 g CH₄) = 0.1558 mol CH₄

Given that 125 kJ of heat is released by 0.1558 mol CH₄, we can determine the amount released by 1 mol CH₄ as:

125 kJ / 0.1558 mol = 802.3 kJ/mol. However, this value should be negative as heat release indicates an exothermic reaction, thus the enthalpy of combustion per mole of methane is -802.3 kJ/mol.

To provide the requested answer choice, we can approximate to the closest option which is -802.3 kJ/mol ≈ -800.0 kJ/mol. Therefore, the correct answer is not listed in the provided options, and a correction may be necessary.