Zadanie 5a, Paper 2, maj 2025, TZ3, Chemia IB HL

(i) «ΔH_c^⊖: C₄H₆ = −2541, H₂ = −286, C₄H₁₀ = −2878 kJ mol⁻¹»

«$\sum \Delta H_\mathrm{c}^\ominus(\text{reactants}) = (-2541) + 2(-286) =$» −3113 «kJ mol⁻¹» AND «$\sum \Delta H_\mathrm{c}^\ominus(\text{products}) =$» −2878 «kJ mol⁻¹» ✔

«$\Delta H^\ominus = \sum \Delta H_\mathrm{c}^\ominus(\text{reactants}) - \sum \Delta H_\mathrm{c}^\ominus(\text{products}) = -3113 - (-2878) =$» −235 «kJ mol⁻¹» ✔

(ii) ΔS^⊖ = −0.231 «kJ K⁻¹ mol⁻¹» OR ΔH^⊖ = −235 000 «J mol⁻¹» ✔

«ΔG^⊖ = 0 = ΔH^⊖ − TΔS^⊖, so $T = \dfrac{-235\,000}{-231} =$» 1020 «K» ✔

(i) M1: sums of the combustion enthalpies of reactants and of products; M2: ΔH = -235 kJ mol^-1 (sign essential). Award [2] for the correct final answer. (ii) M1: ΔH and ΔS expressed in consistent units; M2: T = 1020 K (accept 1017 K). Award [2] for the correct final answer; with -150 kJ mol^-1 the answer is 649 K. No ECF for M2 if a negative temperature is obtained.