The heat of combustion of hydrogen gas is –286 kJ/mol. What is this value expressed in kJ/g?

• A. –2.86 kJ/g
• B. –286 kJ/g
• C. –143 kJ/g
• D. –13.0 kJ/g

Answer: (D)

Verified step by step guidance

1. Identify the given information: the heat of combustion of hydrogen gas is –286 kJ per mole (–286 kJ/mol).
2. Recall that to convert from kJ/mol to kJ/g, you need to divide the energy per mole by the molar mass (in grams per mole) of hydrogen gas (H₂).
3. Calculate the molar mass of hydrogen gas (H₂). Since each hydrogen atom has an atomic mass of approximately 1.008 g/mol, the molar mass of H₂ is \$2 \times 1.008 = 2.016$ g/mol.
4. Set up the conversion using the formula: \(\text{Heat of combustion in kJ/g} = \frac{\text{Heat of combustion in kJ/mol}}{\text{Molar mass in g/mol}} = \frac{-286}{2.016}\).
5. Perform the division to find the heat of combustion per gram, which will give the value in kJ/g.