Chemical Reactions and Collision Theory

Chemistry I 2007

Chemical reaction Format

Generic Format

A + B C + D

Reactants Products

Substances being mixed

LHS of arrow

Substance being made

RHS of arrow

“Yield” = reaction taking place

Types of Chemical Reactions

5 main types of Chemical Reactions

1) Synthesis

2) Decomposition

3) Single Displacement

4) Double Displacement

5) Combustion

Synthesis

Synthesis means “to make”

Generic RXN

A + B C

Always

makes

1 product

Real Life reaction

Fe

Iron main component in steel

Oxygen

Iron (III) Oxide

AKA RUST

Fe2O3+ O2

DecompositionDecomposing video

Generic Reaction

A B + C

Only 1 Reactant

Real Life Reaction

H2O2 H2 + O2

Hydrogen Peroxide

Single Displacement

Generic Reaction

A + XY X + AY

OR

A + XY Y + XA

Metal for a metal

Non-metal for a Non-metal

Single Displacement

A + XY X + AY

Always a Single Element

Always a Compound (2 or more elements)

Single Displacement

Al + HCl H2 + AlCl3

Single Element

Compound (2 or more elements)

Double Displacement

Generic Reaction

AB + XY XB + AY

2 Compounds

(2 or more elements bonded together)

Double displacement

KI + Pb(NO3)2

Compound 1 Compound 2

PbI2 + KNO3

K and Pb switch

CombustionGeneric reaction

CxHy + O2 CO2 + H2O

ALWAYSHydrocarbon

Burning a substance in the presence of oxygen (O2)

Combustion

C8H18 + O2 CO2 + H2O

Octane

Gasoline

CH3OH + O2 CO2 + H2O

Methanol

Chemical Reaction Review

Generic Format of reaction

5 different types of chemical reactions

A + B C + D

Reactants Products

A + B C + D

Products

1) Synthesis

2) Decomposition

3) Single Displacement

4) Double Displacement

5) Combustion

How do reactions occur?

Collision Theory Collision TheoryCollision Theory

In order for a chemical reaction to take place, the reactants must collide.

The collision transfers kinetic energy needed to break the necessary bonds so that new bonds can be formed.

Collision requirements

Requirement 1Must have the proper orientation. 2HCl + Mg MgCl2 + H2

H---ClMgWrong Orientation

H-Cl MgH Cl-Mg Correct Orientation

Collision requirements

Requirement 2

Mg

Must have enough kinetic energy to reach a threshold of energy called activation energy

H---Cl H---Cl MgH Cl--Mg

Energy of Activation

Energy of Activation

Increasing the Rate of Reactions

What needs to happen in order for the rate of the chemical reaction to increase (go faster)?

More collisions = Faster reaction rate

4 Factors that cause more collisions

1) ____________

2) ____________

3) ____________

4) ____________

5th way in increase Rxn Rate

Add a Catalyst = Speeds up a reaction but is not used in the reaction

Lowers the activation energy

Summary• Molecules must collide with the correct

orientation and enough energy in order to react.

More collisions Faster the reaction rate.

Increase Temperature, Concentration, Pressure, and surface area results in more collisions therefore faster reactions.

Adding a catalysts lowers the energy of activation thus faster reaction rate.