Chemical energetics and fuel cells

Learning objectives

State that an exothermic reaction transfers thermal energy to the surroundings so the temperature of the surroundings rises, and an endothermic reaction takes in thermal energy so the temperature falls, and identify examples of each

Interpret reaction pathway diagrams for exothermic and endothermic reactions and, at Extended, state that the transfer of thermal energy during a reaction is the enthalpy change, ΔH, which is negative for exothermic and positive for endothermic reactions

Define activation energy, Ea, as the minimum energy that colliding particles must have to react, and draw and label reaction pathway diagrams showing reactants, products, ΔH and Ea (Extended)

Explain that bond breaking is endothermic and bond making is exothermic, so the sign and size of ΔH depend on the balance between the energy needed to break bonds and the energy released when new bonds form (Extended)

Calculate the enthalpy change of a reaction from bond energies (Extended)

State that a hydrogen–oxygen fuel cell uses hydrogen and oxygen to produce electricity with water as the only chemical product and, at Extended, describe the advantages and disadvantages of fuel cells compared with petrol engines in vehicles