Chapter summary
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13.3 Law of constant composition
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Chapter summary
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Matter does not stay the same. It may undergo physical or chemical changes.
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In a physical change the chemical identity of a substance does not change. Mass and the number of atoms of each element are both conserved. Physical changes usually involve relatively small changes in energy.
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During a physical change, the arrangement of particles may change but the mass, number of atoms and number of molecules will stay the same.
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Physical changes involve small changes in energy and are easily reversible.
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A chemical change occurs when one or more substances change into other materials. A chemical reaction involves the formation of new substances with different properties. For example, hydrogen and oxygen react to form water
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A chemical change may involve a decomposition or synthesis reaction. During a chemical change, the mass and number of atoms is conserved, but the number of molecules is not always the same.
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Chemical reactions involve large changes in energy. Chemical reactions are not easily reversible.
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The law of conservation of mass states that the total mass of all the substances taking part in a chemical reaction is conserved and the number of atoms of each element in the reaction does not change when a new product is formed.
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The law of constant composition states that in any particular compound, all samples of that compound will be made up of the same elements in the same proportion or ratio.
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Gay-Lussac's Law states that in a chemical reaction between gases, the relative volumes of the gases in the reaction are present in a ratio of small whole numbers if all the gases are at the same temperature and pressure.
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13.3 Law of constant composition
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