1. 1 Chapter 6 Chemical Reactions Objectives Write balanced chemical equations Identify types of chemical reaction

2. 2 Every minute of the day chemical reactions take place - both inside you and around you. Dalton: As reactants are converted to products, bonds holding atoms together are broken and new bonds are formed.As reactants are converted to products, bonds holding atoms together are broken and new bonds are formed. Atoms are neither created nor destroyed, just rearrangedAtoms are neither created nor destroyed, just rearranged

3. 3 (In writing reactions, separate the reactants from the products by writing an arrow (  ), which means “yields, gives, reacts to, or produces”) The example used here is described in a “word equation” Reactants  Products Carbon + oxygen  carbon dioxide

4. 4 Better than word equations are chemical equations Iron + oxygen  iron (III) oxide Fe + O 2  Fe 2 O 3 “Skeleton equation” Skeleton equation does not indicate the relative amounts of reactants and products. They are not “balanced”

5. 5 Symbol Used in Chemical Equations

6. 6 Fe (s) + O 2 (g)  Fe 2 O 3 (s) MnO 2 H 2 O 2 (aq) -----  H 2 O (l) + O 2 (g) catalyst A catalyst is a substance that speeds up the rate of a reaction but is not used up in the reaction. Because its neither reactant nor product it is written above the arrow.

7. 7 Balancing Equations An equation that gives the correct quantity of each reactant and product is called a balanced equation. coefficients Numbers before ‘components’ are called coefficients

8. 8 For a correct chemical equation First write correct formulas for all reactants and products. Second balance the equation so that each side of the equation has the same number of atoms of each element. C (s) carbon O 2 (g) oxygen CO 2 (g) Carbon dioxide Reactants 1 carbon atom 2 oxygen atoms Product 1 carbon atom 2 oxygen atoms

9. 9 H 2 (g) hydrogen O 2 (g) oxygen H 2 O (l) water Reactants 2 hydrogen atoms 2 oxygen atoms Product 2 hydrogen atoms 1 oxygen atom balanced?

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11. 11 Balance the following equations (on your need to know sheet) MnO 2 H 2 O 2 (aq) -----  H 2 O (l) + O 2 (g) Al (s) + O 2 (g)  Al 2 O 3 (s) Mg (s) + HCl  MgCl 2 (s) + H 2 (g)

12. 12 Balance the following equations Fe (s) + O 2 (g)  Fe 2 O 3 (s) Fe 3 O 4 (s)  Fe (s) + O 2 (g) Carbon and chlorine gas react to carbon tetrachloride.

13. 13 Exothermic: Energy is being released (test tube getting hot) = energy written with the products (on the right) CH 4 (g) + 2 O 2 (g) --  CO 2 (g) + 2 H 2 O (g) + energy Endothermic: Energy is being absorbed (test tube getting cold) = energy written with the reactants (on the left) 2 H 2 O (l) + energy --  2H 2 (g) + O 2 (g)