What is the standard enthalpy of formation (ΔH_f^ext{°}) for CH_4(g) in kJ/mol?

• A. -74.8
• B. -241.8
• C. -285.8
• D. 0

Answer: (A)

Verified step by step guidance

1. Understand that the standard enthalpy of formation, \(\Delta H_f^{\circ}\), is defined as the enthalpy change when one mole of a compound is formed from its elements in their standard states under standard conditions (usually 1 atm and 25°C).
2. Identify the elements involved in forming methane (CH\(_4\)): carbon (C) in its standard state (graphite) and hydrogen (H\(_2\)) gas in its standard state.
3. Write the formation reaction for methane from its elements in their standard states: \(\mathrm{C (graphite) + 2H_2 (g) \rightarrow CH_4 (g)}\).
4. Recall or look up the standard enthalpy of formation values for methane (CH\(_4\)) from a reliable data source or textbook, which is typically given in kJ/mol.
5. Select the value that corresponds to the enthalpy change for the formation reaction above, which is the standard enthalpy of formation \(\Delta H_f^{\circ}\) for CH\(_4(g)\).