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What is the difference between a physical and a chemical change?

April 26, 2017chemical Chemistry difference Mathematics physical

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What is the difference between a physical and a chemical change?

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Physical changes are those that take place with no change in the chemical composition of the substance…Sawdust is still wood, torn up paper is still paper, water can be solid, liquid or gas but is still H2O. Chemical changes are those in which the actual substances become other substances by chemical reaction resulting in the formation of a new substance which has completely different properties from those of the Elements of their composition. Hydrogen (H2) and Oxygen (O2) gases, when chemically combined form water vapour by combustion of the hydrogen. 2H2 + O2 = 2H2O. (Oxygen itself doesn’t burn but is necessary for combustion). Water will not burn and can extinguish fire. Sodium (Na) solid, and Chlorine (Cl2) gas are both dangerous Elements. When chemically combined, they form Common Salt (NaCl) used for food flavouring. 2Na + Cl2 = 2NaCl. (Some chemical reactions are reversible).