1. Chemical Reactions SCH 3U Unit 2 Part 2

2. Chemical Equations Word Equations – a way to describe chemical reactions using chemical names; it tells you what reacts and what is produced. iron + oxygen  iron (III) oxide reactantsproducts

3. Skeleton Equations Skeleton Equations – a way to describe chemical reactions using chemical formulas; it tells you what reacts and what is produced. Fe + O 2  Fe 2 O 3 Fe OO O O O

4. Balanced Equations Balanced Chemical Equations - a chemical equation in which the reactants and products contain the same number of atoms of each element. 4 Fe + 3 O 2  2 Fe 2 O 3 Fe O O O O O OOO OO OO

5. Why balance an equation? Chemical equations must be balanced to obey the Law of Conservation of Mass.

6. Law of Conservation of Mass Law of Conservation of Mass – In a chemical reaction, the total mass of the reactants must equal the total mass of the products. OR Atoms cannot be created or destroyed during a chemical reaction.

7. Balancing an Equation To balance a chemical equation, you must add coefficients in front of each compound in the reaction. 2 K + 2 H 2 O -----> 2 KOH + H 2

8. Balancing an Equation Two things you CANNOT do to balance a chemical reaction: 1) You cannot change the subscripts. H 2 O not H 2 O 2 2)You cannot place a coefficient in the middle of a formula. H 2 O not H 2 2O

9. Balancing an Equation Things to remember about balancing chemical equations: 1)If no coefficient appears in front of the symbol/formula, it is assumed that it is 1 (one). 2) The coefficients must be in lowest terms. 4H 2 + 2O 2  4H 2 O 2H 2 + O 2  2H 2 O

10. To Balance an Equation Balance all metals. Balance all non-metals (except hydrogen and oxygen). Balance hydrogen or oxygen (whichever is not by itself). Balance the remaining atoms. Count the number of atoms of each element on each side of the equation. THEY SHOULD BE EQUAL.

11. Practice 1. ____ K + ____ CaCl 2 -----> ____ KCl + ____ Ca 2. ____ HCl + _____ Mg(OH) 2  _____ H 2 O + _____ MgCl 2

12. More Practice 3._____ KNO 3 ----> _____ KNO 2 + ____ O 2 4._____C 2 H 2 + _____O 2 -----> _____CO 2 + _____ H 2 O 5._____C 4 H 8 + _____O 2 ----> ______ CO 2 + _____ H 2 O 6._____ Hg + _____ O 2 ----> ______ HgO 7. ______ AgNO 3 + ______NaCl ----> ______AgCl + _____NaNO 3

13. Time to get to Work Pg 115 #1-10 Pg 117 #1-6 Pg 120 #11-20