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3.1: Prelude to Thermochemistry

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    Chemical reactions, such as those that occur when you light a match, involve changes in energy as well as matter. Societies at all levels of development could not function without the energy released by chemical reactions. In 2019, about 80% of US energy consumption came from the combustion of fossil carbon energy sources, 8% from nuclear reactions, and 11% from renewable sources. We use this energy for residential energy (16%); to transport food, raw materials, manufactured goods, and people (37%); for industrial production (35%); and for commercial facilities (12%).1 While these energy systems help us meet our essential needs, combustion of the fossil fuel sources are the primary contributor to global anthropogenic climate change.

    Figure \(\PageIndex{1}\): Sliding a match head along a rough surface initiates a combustion reaction that produces energy in the form of heat and light. (credit: modification of work by Laszlo Ilyes).

    Useful forms of energy are also available from a variety of chemical reactions other than combustion. For example, the energy produced by the batteries in a cell phone, car, or flashlight results from chemical reactions. This chapter introduces many of the basic ideas necessary to explore the relationships between chemical changes and energy, with a focus on thermal energy.


    1. US Energy Information Administration, Total Energy, Annual Energy Review  Data derived from US Energy Information Administration (August 2020).

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