Chapter Seven Chemical Reactions Lesson 7 1 Chemical

Chapter Seven: Chemical Reactions Lesson 7. 1 Chemical Changes Lesson 7. 2 Conservation of Mass

Investigation 7. 1 Identifying Chemical Changes • How can you identify when chemical changes occur?

7. 1 Chemical Changes • 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?

Chemical reactions • The process of making pizza involves some physical changes (like chopping vegetables). • The processes used by yeast in the dough or by the gas stove to bake the pizza are chemical changes. • Any time there is a chemical change, a chemical reaction has occurred.

Chemical Reactions • The process used to generate heat in a gas stove to bake the pizza is a chemical reaction.

Evidence of chemical reactions Four indicators of chemical change are: 1. 2. 3. 4. Formation of new gas Formation of new solid Color change Temperature change (Energy is released or absorbed)

Reactants and products • 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 formed in the chemical reaction.

Reactants and products • In this reaction, methane (a natural gas) is burned. • Some energy is added to get the reaction started.

Reaction symbols • The small symbols in the parentheses (s, l, g, aq) next to each chemical formula indicate the phase of each substance in the reaction.