17.1 Chemical Reactions A chemical reaction is the process of breaking of chemical bonds in one or more substances, and the reforming of new bonds to create new substances. When you make pizza, which changes are physical and which are chemical changes?

17.1 Evidence of chemical change Four indicators of chemical change are: 1.Formation of new gas 2.Formation of new solid 3.Release of energy (heat or light) 4.Color change

17.1 Products and reactants In chemical reactions, you start with reactants that are combined to make products. – The reactants are the starting substances. – The products are the new substances which result from the chemical reaction.

12.1 Properties of Solids Properties that can only be observed when one substance changes into a different substance are called chemical properties. Any change that transforms one substance into a different substance is called a chemical change. Ex. If you leave a nail outside, it rusts.

12.1 Properties of Solids A physical change is any change in the size, shape, or phase of matter in which the identity of a substance does not change. For example, when water is frozen, it changes from a liquid to a solid.

10.3 Phases of Matter On Earth, pure substances are usually found as solids, liquids, or gases. These are called phases of matter.

10.3 The phases of matter A solid holds its shape and does not flow. The molecules in a solid vibrate in place, but on average, don’t move far from their places.

10.3 The phases of matter A liquid holds its volume, but does not hold its shape—it flows. Liquids flow because the molecules can move around.

10.3 The phases of matter A gas flows like a liquid, but can also expand or contract to fill a container. A gas does not hold its volume. The molecules in a gas have enough energy to completely break away from each other.