When substances react chemically, their energy is either released, absorbed, or converted to other forms of energy. For example, when striking a match, the chemical energy stored in the match-head is transformed into heat and light energy. Atomic energy is the energy released by the splitting of an atom as in a nuclear reactor. When you do physical exercise the chemical energy stored in the carbohydrate, fat, and other molecules in the cells of your body is converted to energy of motion. Heat energy within the Earth creates change through the activity of volcanoes and distortion of the Earth's crust.
Chemical energy creates change by being the basis of metabolism in plant and animal life.
The amount of energy needed for one gram of ice to change to water is 80 calories. In this situation loosely packed molecules of water vapor release energy as they become more closely packed together to become liquid water. This is why a burn from steam from boiling water in a tea kettle can be more severe than a burn from the hot water in the kettle. In animals and plants the amount of stored energy can be measured using a 'bomb calorimeter'. In this device a sample of plant or animal material can be converted to heat energy which is measured as an increase in temperature.