A reaction converts one molecule of AB(g) and one molecule of C2(g) into two molecules of AC(g). A text-based diagram displays the average bond energies involved (in kJ mol⁻¹):
• Bonds present in the reactants: AB = 340, C–C = 610
• Bonds present in the products: A–C = 420 (per bond)
Without performing a detailed calculation, state whether the reaction is exothermic or endothermic and briefly justify your choice based on the numerical values shown.