Chapter summary

Chapter summary

Presentation: VPdwh

• Matter does not stay the same. It may undergo physical or chemical changes.

• 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.

• During a physical change, the arrangement of particles may change but the mass, number of atoms and number of molecules will stay the same.

• Physical changes involve small changes in energy and are easily reversible.

• 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

• 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.

• Chemical reactions involve large changes in energy. Chemical reactions are not easily reversible.

• 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.

• 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.

• 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.