The standard internal energy change of formation, Δ_fU°, of CH₄(g) at a certain temperature is –393 kJ mol⁻¹.
Find the value of the standard enthalpy of formation (Δ_fH°).

1. Zero
2. Less than Δ_fU°
3. Greater than Δ_fU°
4. Equal to Δ_fU°