CHAPTER 9 CHAPTER 9 CHEMICAL REACTIONS AND CHEMICAL REACTIONS AND

EQUATIONSEQUATIONS

Law of conservation of Law of conservation of MatterMatter

Mass is conserved in chemical Mass is conserved in chemical reactions reactions

Mass of products = mass of Mass of products = mass of reactantsreactants

2H2H22 + + OO22 →→ 2H2H22OO

4 amu + 32 amu = 2 (18 amu)4 amu + 32 amu = 2 (18 amu)

The atoms of each element The atoms of each element are also conserved.are also conserved.

2H2H22 + + OO22 →→ 2H2H22OO

4 H atoms, 2 O atoms 4 H atoms, 2 O atoms →→ 4 H atoms 4 H atoms and 2 O atoms and 2 O atoms

BALANCING CHEMICAL EQUATIONSBALANCING CHEMICAL EQUATIONS

When you are given an equation to balance When you are given an equation to balance the chemical formulas will be correct. DO the chemical formulas will be correct. DO NOT CHANGE THESE.NOT CHANGE THESE.HH22 ++ OO22 →→ HH22OONote (diatomic elements are marked with a Note (diatomic elements are marked with a green X on the periodic chart at the front of green X on the periodic chart at the front of the room.)the room.)Balance equations by placing coefficients in Balance equations by placing coefficients in front of the formulas.front of the formulas.Balance only one element (or polyatomic ion) Balance only one element (or polyatomic ion) at a time until the entire equation is balanced. at a time until the entire equation is balanced.

Complete balancing worksheetComplete balancing worksheet

CLASSIFYING CHEMICAL CLASSIFYING CHEMICAL REACTIONSREACTIONS

Combination reactionCombination reaction (also called (also called synthesis)synthesis)

AA ++ B B →→ AB AB

Identified by two reactants only one Identified by two reactants only one productproduct

NaNa ++ ClCl22 →→ NaClNaCl

COCO22 + H + H22O O →→ H H22COCO33

Decomposition ReactionDecomposition Reaction

Exact opposite of combination reactionExact opposite of combination reaction

One compound is broken down One compound is broken down “decomposed” into two.“decomposed” into two.

Often energy has to be added to make Often energy has to be added to make this happen.this happen.

AB AB →→ A + BA + B

HH22COCO33 →→ COCO22 + + H H22O O

Single Replacement Single Replacement ReactionsReactions

OneOne element kicks another element out element kicks another element out of a compound and takes its place.of a compound and takes its place.A + BX A + BX → AX + B→ AX + BA more reactive metal will replace a A more reactive metal will replace a less reactive metal or hydrogen. less reactive metal or hydrogen. (See metal activity series page 295)(See metal activity series page 295)A more reactive nonmetal will replace A more reactive nonmetal will replace a less reactive nonmetal (compare a less reactive nonmetal (compare electronegativity) electronegativity)

Double Replacement Double Replacement ReactionReaction

Compounds with positive and negative Compounds with positive and negative groups exchange partners.groups exchange partners.AX + BY AX + BY → AY + BX→ AY + BXCaCOCaCO33 + HCl → CaCl + HCl → CaCl22 + H + H22COCO33

The 4 ions of the starting materials are all The 4 ions of the starting materials are all dissolved in water and no reaction will take dissolved in water and no reaction will take place unless:place unless:– A molecular compound is formed (like water)A molecular compound is formed (like water)– A precipitate is formed (check the solubility of A precipitate is formed (check the solubility of

possible products)possible products)– A gas that leaves the solution is formedA gas that leaves the solution is formed

When will a reaction not When will a reaction not take place?take place?

A metal will not react with a metal.A metal will not react with a metal.

A noble gas will not react with A noble gas will not react with anything. anything.

A less reactive element will not A less reactive element will not replace a more reactive element.replace a more reactive element.