Practice question
Question
What is the change in internal energy ( Δ U ) for the vaporization of 1 mol of water at 373 K if Δ H = 40.79 kJ/mol ? ( R = 8.314 J/mol·K )
Explanation
For H₂O(l) → H₂O(g) , Δ ng = 1 . Using Δ H = Δ U + Δ ng RT , where RT = 8.314 × 373 × 10⁻³ = 3.1012 kJ , we get Δ U = Δ H - Δ ng RT = 40.79 - 3.1012 = 37.69 kJ/mol .