Reaction Rates

Ch. 13.1

Kinetics and

Reaction Rate

• Kinetics is the area of chemistry

dealing with the speed or rate at

which reactions take place.

• Some reactions act quickly. (air bags)

• Some reactions react slowly. (rusting)

What is a Rate?

• Fixed ratio between two

things

• It measure how fast or slow a

reaction or an action takes

place.

Why Rates Important?

• It is important to understand

rates in order to control the

reaction.

Fires have fast rates,

that must be controlled

Fire Triangle

Understanding Rates

• Chemists, engineers, and

everyday chefs need to be

aware how reaction rates can

change when conditions for the

reaction change.

REACTION RATES ! !

RR = D [reactants ]

D t

RR = D [products ]

D t

Collision Theory

•Reactions and the rate of

reactions taking place

depend on two or more

molecules colliding in

such a way that old bonds

break and new bonds

form.

COLLISION THEORY

• C = collisions

• E = energy

• O = orientation

Collisions

• Reactants must be in contact in

order to react.

Energy

• Every reaction needs energy

to get things started.

(Activation Energy)

• Energy to form activated

complex

Energy

1. Exothermic Reaction

-A process that loses heat to

surrounding.

-surrounding get hotter

-Products are lower in energy than

reactants

2. Endothermic Reaction

-A process that absorbs heat from

surrounding.

-surrounding get colder

-Products are higher in energy

than reactants

Energy Diagram

Orientation

• Reactants must be lined up

properly when colliding.

Factors Affecting

RXN Rates

• Nature of Reactants

• Temperature

• Concentration

• Surface Area

• Catalysts/inhibitors

Nature of Reactants

• Not all materials react with

each other.

• If reactants don’t have

enough energy, no reaction

can take place.

• If reactants don’t collide in

the proper orientation, no

reaction takes place.

Nature of reactants

Collisions

Collisions

Energy

Collisions

Energy

Orientation

NO

NO

YES

Temperature• Higher the temperature the

faster the reaction.

• Higher temperature causes

particles to move faster, thus

they collide more often.

• Raising the temperature only

100C will double the reaction

rate

Concentration (M)

• The more concentrated a solution

the faster the reaction will be.

• If the number of reactant

particles per unit volume

increases, then the chance of

successful collisions increase.

• Double the concentration of

reactants can quadruple the rate.

Which has a higher concentration of reactants?

More concentrated

Surface Area

(particle exposure)

• The greater the surface area

the faster the reaction.

• More surface area means

more reactants are in

contact, which of course

leads to more collisions.

Surface AreaMore it can be broken down a more area

MORE

kindle

groundLESS Whole bean

Logs

a

a

Catalyst• A substance that changes

the rate of chemical

reactions without being

permanently changed itself.

• Brings energy to reaction

• Lowers the activation

energy required.

• Ex. yeast, enzymes

Inhibitors

•Inhibitors slow down

reactions by tying up

the reactants

•Ex. preservatives

Rate Review

Reversible

Reactions and

Equilibrium

Ch 13.2

Reactions Going

Completion

• products are removed from

the reacting system

(3 examples)

1. Forming a insoluble

precipitate (no ions left)

2. Forming a gas

3. Neutralized water

Removing a Product

• gas formed (g)

• 2H2O 2H

2(g) + O

2 (g)

• Precipitate formed (s)

CuSO4

+Na2SNa

2SO

4(aq) + CuS(s)

• Water is formed (H2O)

• NaOH + HCl NaCl + H2O

Reversible

Reactions

3H2

+ N2

↔ 2NH3

• the products remain in the system so

they may react back to original

reactants.

• Two reactions where the only

difference is the direction.

• Reactions are occurring at the same

time.

Equilibrium

•The state in which a

chemical reaction

and its reverse

reaction occur at the

same rate.

Examples:

Reversible Reactions.

• Unopened Soda

• Breathing cycle

• Rechargeable batteries

• Mood rings

1. Equilibrium

is reached

when rates

are equal

2. No change

in the

amounts.

Ch. 13.5

Le Chatelier’s Principle

Ch. 13.5

Le Chatelier’s Principle

•If a system at

equilibrium is

stressed, it will react

to undo the stress.

STRESS to SYSTEM

Three stress’s are

1.Temperature

2.Concentration

3. Pressure.

(change in volume)

Le Chatelier’s Principle

• If disturbed by a stress, a net

shift (left or right) will occur to

offset the change.

• A shift represents the

formation of more reactants or

products. (opposite to the shift

is consumed)

When a stress is applied the

reaction will reestablish equilibrium

Equilibrium = No change in amount over time

1. Concentration

Equilibrium

Reactants

Products

Equilibrium reached

when concentrations

become constant

2. Temperature

Heat +

3. Pressure

The side with

least moles

The side with

most moles

LEFT: RIGHT:

↔

Stress, Shift, Change In

Concentration