Chemical changes occur when substances combine to form a new substance called synthesis and are usually irreversible. A chemical reaction causes the atoms of substances to rearrange and change their properties or composition, giving rise to at least one new substance. Chemical reactions can also cause a substance to break down, giving rise to two or more different substances. Many natural and man-made chemical changes occur daily. The two main natural chemical changes are: combustion for example; wood combustion and the metabolism of the human body. Two man-made chemical changes are: gas bombs used in the military and rust or iron (nails). Combustion is a chemical combination or change resulting in the production of heat and light. Essentially, wood burning is one of the primary forms of combustion. When wood is burned, the carbon in the wood reacts against the oxygen in the air, which then creates ash and smoke causing a chemical change. This creates energy in the form of heat and light. Combustion is an irreversible chemical change, ashes cannot be transformed into wood. Wood is used as a heating source and in many areas wood is the most readily available form of fuel. There are many divergent uses of wood burning in everyday life, one of the main ones being the ability to create heat, for example; in a chimney for residential heating. Wood is a renewable fuel for heating and electricity production. Wood combustion is the greatest energy acquired from solid fuel biomass. In countries like the United States, firewood is the second most widely used form of renewable energy. In other countries, there is growing interest in using wood waste as fuel for domestic and industrial heating. There are many advantages...... middle of paper ......r Ovens. [online] Available at: http://www.heatmasterss.com/benefits-of-wood-burning [Accessed May 11. 2014].Lai, J. (2014). Disadvantages of burning wood | eHow. [online] eHow. Available at: http://www.ehow.com/info_7833898_disadvantages-burning-wood.html [Accessed May 14. 2014].Pilling, M. and Robertson, S. (2003). Main equation models for important chemical reactions in combustion. Annual Review of Physical Chemistry, 54(1), pp.245--275.Walker, D. (2007). Chemical reactions. 1st ed. London: Evans Brothers.Worldwildlife.org, (2014). Deforestation | Threats | WWF. [online] Available at: http://www.worldwildlife.org/threats/deforestation [Accessed May 20. 2014].Www2.estrellamountain.edu, (2014). CHEMISTRY I: ATOMS AND MOLECULES. [online] Available at: http://www2.estrellamountain.edu/faculty/farabee/biobk/biobookchem1.html [Accessed May 20. 2014].