Enthalpy Changes (OCR A-Level Chemistry A): Flashcards

$H$, total heat energy in chemical system

$\Delta H$

Negative (products have less energy than reactants)

Positive (products have more energy than reactants)

$E_a$, minimum energy required for a reaction to occur

100 kPa and 298 K (25°C)

Enthalpy change forming 1 mole of compound from elements

0 kJ mol⁻¹

Enthalpy change when 1 mole burns completely in oxygen

-57 kJ mol⁻¹