1 Chemical Reactions

2  Chemical Reaction = Chemical Change  Chemical Rxn – the process by which the atoms of one or more substances are rearranged to form NEW, different substances  Evidence of chemical rxns: - temperature change - odor - color change - gas bubbles - formation of a solid (precipitate)

3 Chemical Equations  In a chemical reaction, the substances you start with are called reactants and the substances produced are called products Reactants  Products the arrow is the “yields” symbol

4 Chemical Equations (cont’d)  Chemical Reactions can be represented by: Word Equations Skeleton Equations Balanced Chemical Equations

5 Word Equations  Word equations show all substances written as words: Sodium + Chlorine  Sodium Chloride

6 Skeleton Equations  Skeleton Equations translate the words into chemical formulas: Na + Cl 2  NaCl **Don’t Forget Diatomic Molecules** I 2, Br 2, Cl 2, F 2, O 2, N 2, H 2

7 Balanced Chemical Equations  Balanced Chemical Equations show all substances written as formulas (like skeleton equations), but also show relative amounts of substances  Atoms cannot be created or destroyed in a chemical rxn, so YOU need to Balance the equation to show this…

8 Balanced Chemical Equations (cont’d)  How to balance an equation: Add coefficients (whole numbers) IN FRONT of the formula of a substance NEVER CHANGE SUBSCRIPTS!!!!

9 Balancing Chemical Equations  TIPS: Balance Oxygen LAST Balance Hydrogen second-to-last If the same polyatomic ion appears on both sides of the arrow, balance it as a whole unit

10 Counting Atoms  How many atoms in each of the following? H 2 O 3H 2 O Al(NO 3 ) 3 2Al(NO 3 ) 3 HC 2 H 3 O 2 4HC 2 H 3 O 2

11 Balancing Equation Examples:

12 Classifying Chemical Rxns  5 Types of chemical rxns: - synthesis (combination) - decomposition - single replacement - double replacement - combustion (complete & incomplete)

13 Synthesis (Combination) Rxns:  Two substances combine to produce ONE PRODUCT A + B  AB Examples: 2 Fe + 3 Cl 2  2 FeCl 3 2 SO 2 + O 2  2 SO 3

14 Decomposition Rxns:  ONE REACTANT breaks down into two or more products AB  A + B Examples: NH 4 NO 3  N 2 O + 2 H 2 O 2 NaN 3  2 Na + 3 N 2

15 Single Replacement Rxns  The atoms of one element replace the atoms of another element in a compound A + BC  AC + B Examples: 2 Al + 3 Ni(NO 3 ) 2  2 Al(NO 3 ) Ni Cu + 2 AgNO 3  2 Ag + Cu(NO 3 ) 2

16 Double Replacement Rxns  The atoms of one compound exchange places with the atoms of another compound AB + CD  AD + CB Example: KCN + HBr  KBr + HCN 2 NaOH + CuCl 2  2 NaCl + Cu(OH) 2

17 Combustion Rxns  Complete Combustion = Oxygen combines with a hydrocarbon to produce CO 2 + H 2 O  Incomplete Combustion = Oxygen combines with a hydrocarbon to produce CO + H 2 O Examples: C 2 H 8 + 4O 2  2CO 2 + 4H 2 O 2CH 4 + 3O 2  2CO + 4H 2 O