Reactivity 1.1 - Measuring enthalpy changes

• Chemical reactions involve a transfer of energy between the system and the surroundings, while total energy is conserved.
• In exothermic reactions, energy increases in the surroundings, but decreases in the system.
• In endothermic reactions, energy decreases in the surroundings, but increases in the system.
• In an exothermic reaction, the products are more stable.
• In an endothermic reaction, the reactants are more stable.
• The standard enthalpy change for a chemical reaction, ΔH⦵ , refers to the heat transferred at constant pressure under standard conditions and states.
• ΔH⦵ can be determined from the change in temperature of a pure substance.
• The units of ΔH⦵are kJmol⁻¹ .