Chemistry · Chapter 5

Reading Enthalpy Diagrams

Pick a real reaction and its energy diagram draws itself. Reverse it, or change how much reacts, and watch the sign and the size of ΔH answer.

The diagramproducts high or low?

EXOTHERMIC enthalpy reactants reactants products products ΔH heat leaves equation arrow length uses a square root scale, so small and large values both show

Choose a reaction

−890.5kJ for the equation as written exothermic

Products sit lower than reactants, so heat leaves the system.

The whole list

Values are standard enthalpy changes near 25 °C. Watch the state labels. Liquid water and water vapor are 44.0 kJ/mol apart, so the same burning reaction gives two different numbers.