Chapter 8:

CHEMICAL EQUATIONS

ANDREACTIONS

Indications of a Rxn

• Heat or light given off

• Bubbling/smoke, gas being released

• Precipitate (solid) forms

• Change in the odor/color

• Chemical indicators turn color

Eqn Writing

• Make sure you have the correct formula for each substance

• Diatomic elements – exist only in pairs, always written with a 2 subscript

H2 O2 N2 Cl2 Br2 I2 F2

Rxn/Eqn Parts

H2 (g) + Cl2 (g) 2 HCl (g)

Reactants Product

(Reagents)

Symbols Meaning

Reversible rxn

Heat added

(formula) Catalyst:speeds up rxn

(s) Solid

precipitate forms

(g) Gas

Gas released

(l) liquid

(aq) Aqueous (in water)

Law of Conservation of MatterAtom values must match on both sides

Balance an eqn with coefficient multipliers

___H2 + ___O2 ____ H2O2 21

___Al2O3 ___ Al + __O2

__Fe(NO3)3 + __KSCN __KNO3 + __Fe(SCN)3

2 4 3

3 31 1

5 Rxn Types

Decomposition Decomposition (analysis)

One Reactant breaking down into two or more products

One or more reactants combine with One or more reactants combine with oxygen, oxygen, OO22 , must invole heat or light , must invole heat or light

Usually takes place with carbon compounds and Usually takes place with carbon compounds and

produces carbon dioxide and waterproduces carbon dioxide and water

CombustionCombustion

CH4 + O2 CO2 + H2O

Single Single ReplacementReplacement

(Displacement)(Displacement)

• One element replacesOne element replaces a a similar element in a similar element in a

compoundcompound

Double Double ReplacementReplacement

• the the interchanging of two ionsinterchanging of two ions from two from two different compounds.different compounds.

•Products usually have a precipitate

Reaction rates

The rate of disappearance of the reactants (concentration per second)

Depends on activation energy and molecule collisions

Factors affecting rate:

1) Type of reactants

ion exchange happens quick

covalent bond rearrangement is slow  

2) Concentration and pressure

higher amount increases the collision rate.

 3) Temperature

– increase it and collision rate increases

4) Catalysts

– increases the rate by lowering activation energy

5) Inhibitors

– used to slow rate, preservatives.