For CH₄(g) + Cl₂(g) → CH₃Cl(g) + HCl(g) , Δ H = -103.00 kJ/mol at 298 K. What is Δ U ? ( R = 8.314 J/mol·K )
For Δ ng = 2 - 2 = 0 , RT = 8.314 × 298 × 10⁻³ = 2.4776 kJ . Using Δ H = Δ U + Δ ng RT , Δ U = -103.00 - 0 = -103.00 kJ/mol .
Ref: NCERT Class 11 Chemistry > Chapter 5: Thermodynamics > Topic: Third Law of Thermodynamics and Applications