Chapter 2.3 Changes of Matter

Review  What is the difference between a homogeneous and heterogeneous mixture? Provide one example of each.  Compare and Contrast molecules and compounds.

Physical Changes  Physical Change – a change of matter from one form to another without a change in chemical properties

Examples

Physical Changes  Physical changes do not change a substance’s identity.  Example  An ice cube melts into water  The water is then heated to form a gas In both cases, it is still water.

Dissolving is a physical change  When you pour salt into water, the salt dissolves.  The salt molecules become spread out between the water molecules.  The molecules of salt and water do not change.

Chemical Changes  Chemical Change – happens when one or more substances are changed into entirely new substances that have different properties.

Examples

Chemical Changes  Chemical changes form new substances  Cannot be reversed by physical means  Anytime food is cooked, it is a chemical change

Signs of a chemical change  Production of gas  Change in odor  Production of sound, heat, or light

Breaking down mixtures and compounds  Mixtures can be separated by physical changes, but compounds must be broken down by chemical changes