So you have to stop… drop… then roll? Chemical Changes Chemical changes- are when a substance changes to form a new or different substance. When a match burns, it changes from wood to charcoal. It is no longer wood. One of the biggest indicators of a chemical change is a change in color of the substance. So you have to stop… drop… then roll?

Examples of chemical change are: Bike chains rusting. Iron combines with oxygen in the air to form rust aka iron oxide (2Fe2O3) Burning wood Burning a wax and a wick in a candle Roasting marshmallow Burn gas in a car Photosynthesis Burning fossil fuel-coal, petroleum, natural gas Living things use chemical changes everyday to grow and gain energy to live.

Chemical Reactions Chemical reactions are the formation of one or more new substances with properties and chemical compositions that differ from the original substance. The atoms of a substance have chemical bonds holding them together. A chemical change occurs when energy like heat is introduced to the substance breaking those bonds. Once the change has occurred you have one or more new substances or chemical reactions.

Endothermic and Exothermic Reactions Endothermic reactions are reactions in which energy is absorbed. For example: plants absorb light to make food in photosynthesis, and an electrolysis device runs an electrical current through water causing water to absorb the energy and release oxygen and hydrogen. Endothermic translates to energy goes in.

Exothermic reactions are reactions in which energy is released Exothermic reactions are reactions in which energy is released. Like fireworks, cellular respiration (where animals break down food for energy) and glow sticks. Exothermic translates to energy comes out or exits.

Exothermic reactions are characterised by : production of light, heat caused by burning or raised temperatures, color change and sound production.

The Law of Conservation of Matter The Law of Conservation of Matter States that matter (atoms) cannot be destroyed or created only changed. In a chemical reaction, this means that the total mass of the substances before a chemical reaction is equal to the total mass of the substance that are produced. If I burn a log in a metal box where no air can escape, the box and log etc inside the box will be the same mass before and after the burning.