Energy is the currency of a modern society - we need it to travel, to produce goods and to heat or cool our buildings. The test of a sophisticated modern society is that energy is used efficiently. The majority of our available energy has been derived from chemical sources - fossil fuels particularly - and the challenge for us is to also develop other sources. They may be chemically based too, perhaps directly converting sunlight which is the ultimate source of all energy on our planet, into clean fuels which can be stored and then used. This module is about measuring the energy changes which accompany chemical processes.