1. Chapter 9: Chemical Reactions The process by which the atoms of one or more substance rearrange to form different substances is called a chemical reaction. Evidences of chemical reactions are… 1.release of heat or light 2.release of bubbles or gas 3.odor 4. color change 5. formation of a solid

2. Representing Chemical Reactions Chemists use equations to represent chemical reactions. Reactants  Products Word equations can be used to represent reactions. A skeleton equation is a correctly written, but unbalanced chemical equation. Because of the law of conservation of mass, all final chemical equations should be balanced. We use coefficients, numbers placed in front of a substance, to balance the equations. See page 286 for steps to balance chemical equations.

3. Balancing Chemical Equations 1.Write a correct skeleton equation. 2.Count the atoms of different elements. 3.Write the coefficient, with the lowest value for each substance that balances the number of atoms in products and reactants. 4.Check your work and reduce the coefficients.

4. Practice Balancing Equations H 2 + Cl 2  HCl Al + Br 2  AlBr 3

5. 9-2 Types of Chemical Equations Synthesis reactions- putting 2 or more substances together to get one product. Combustion reactions- ‘burning’ a reactant with oxygen to produce CO 2 and water. (incomplete combustion produces CO instead of CO 2 ) Decomposition reactions- breaking one reactant up into two or more products. Single replacement reactions-atoms of one reactant replace atoms of another reactant. Double replacement reactions- atoms of 2 ionic compounds, or water, swap partners.