Formaldehyde may be produced in the reaction between methanol and oxygen: 2 CH₃OH (l) + O₂ (g) → 2 HCHO (g) + 2 H₂O (l): ΔH˚_г = —326.2 kJ/mol. The standard heat of combustion of hydrogen is

H₂ (g) + ½ o₂ (g) → H₂O (l): ΔH˚_г = —285.8 kJ/mol

(a) Use these heats of reaction and Hess’s law to determine the standard heat of the direct decomposition of methanol to form formaldehyde: CH₃OH (1) → HCHO (g) + H₂ (g)

(b) Explain why you would probably use the method of part (a) to determine the heat of the methanol decomposition reaction experimentally rather than carrying out the decomposition reaction and measuring ΔH˚_г directly.