Chapter 13 Chemical Reactions

Physical Changes – The change of a substance from one state to another Physical Changes – The change of a substance from one state to another. Usually easy to reverse. No new substance is formed. e.g. Jelly setting in the fridge, chopping onions. A mixture is an example of a physical change because it is easy to remove the individual parts.

Chemical Changes (Chemical Reactions) A completely new substance is formed in a chemical change. A chemical change usually cannot be easily reversed and it involves an energy change.

Exothermic Process A process that involves heat being given out Exothermic Process A process that involves heat being given out. Ex = Exit Eg. Water turning to ice. Endothermic Process A process that involves heat being taken in. En = Entry Exothermic and endothermic processes may be physical or chemical changes.

Signs of a Chemical Reaction 1. Gas is produced. 2. A colour change or cloudiness may occur 3. Heat, light, sound or electricity may be produced

Reactants & Products Reactants – Substances that are present before the reaction takes place Products – Substances that are formed by the end of the chemical reactions. Vinegar + baking soda  Carbon Dioxide + Sodium Acetate + Water Reactants Products Photosynthesis Reaction? Respiration Reaction? Chemical Digestion?

Photosynthesis Carbon Dioxide + Water -> Glucose + Oxygen Respiration Glucose + Oxygen -> Carbon Dioxide + Water Chemical Digestion Starch -> Maltose Other Reactions Methane + Oxygen -> Carbon Dioxide + Water Vapour

Law of Conservation of Mass States that matter cannot be created or destroyed but can only be changed from one form to another In any chemical reaction the total mass of the reactants is always equal to the mass of the products.

Activation Energy The minimum energy needed to start a chemical reaction A certain amount of energy has to be used to strike the match. A much bigger amount of energy is released as heat and light when the match lights.

Exothermic and Endothermic Reactions

Reaction Rates The speed of a reaction is called its reaction rate Reaction Rates The speed of a reaction is called its reaction rate. The reaction rate can be fast or slow Slow reaction: rusting Fast reaction: explosion

Particle Collisions and Reaction Rates Collisions between particles at what cause chemical reactions. The more collisions there are between two substances the more likely they are to react. The faster they move the more likely these collisions will result in a chemical reaction.