Ch. 2-3 Chemical Properties

Chemical Properties – describe matter based on its ability to change into new matter that has different properties

Examples: 1. Flammability – the ability of a substance to burn When wood burns, it can turn into ashes and smoke which have different properties than when it started

2. Reactivity – the ability of two or more substances to combine and form one or more new substances The iron in an old car left outside can form rust when it is exposed to oxygen

3. pH – a measure of the acidity or basicity of a substance Measured on a scale from 0-14 A pH lower than 7 means an acid A pH higher than 7 means a base A pH exactly at 7 means a neutral solution

Chemical Change – occurs when a substance changes its identity into new substances Chemical changes occur because chemical reactions have taken place

Examples: Burning a piece of paper Vinegar and baking soda bubble up due to the reaction of an acid and a base. Sour milk because bacteria have formed new substances in the milk A battery creating an electrical charge Our body digesting food A rusty metal mailbox

Common signs that show a chemical change has occured: A change in temperature (either produce heat or absorb heat) A change in color Producing a solid particle or a gas

Can physical and chemical changes be reversed? Many physical changes are easily reversed. ex- water can be frozen and then melt back Most chemical changes cannot be reversed. ex- after burning a piece of wood, the ashes cannot be made back into a piece of wood