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I have learned about a type of storing energy is chemical energy. But energy isn't sth we can see, can touch. It just simply gives the ability to work. So how can energy be contain in such chemical things like above?

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    $\begingroup$ Well, just like that: you lit a match, and you see the energy coming out of it. $\endgroup$ Jun 10 '18 at 12:06
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Yes, energy isn't a "substance" it is the ability to do work. But chemicals can still store it.

The key to understanding how is the relative amount of energy in different chemicals. Some chemical reactions release heat because the products of the reaction are lower energy than the chemicals that react (reactions are a bit more complicated than this in reality and some are driven by changes in entropy but that isn't important for understanding simple reactions). A candle, for example, consists of a mixture of long chain hydrocarbons with a formula approximating CH2. A candle will burn in air (reacting with molecules of oxygen) to give a mixture of CO2 and H2O. This reactions releases heat (simplifying slightly) because the bonds making up the products have lower energies than the bonds making up the candle wax.

This is why we can say that chemicals "store" energy. But we should always be careful to specify the reaction involved as chemical energy is stored relative to the possible products from a reaction not in some absolute sense.

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  • $\begingroup$ I'm still not 100% understand but this has satisfied me. Thank you very much! $\endgroup$ Jun 10 '18 at 14:43

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