CHEM - Kinetics

Kinetics tells us

how fast a reaction occurs

Rate of reaction is the

change in the amount of reactant/product per unit of time

oxygens oxidation number is usually

-2

equation for finding the rate

Rate=Δ[A]​/Δt

Finding the rate of a product will be

positive

Finding the rate of a reactant will be

negative

List five factors that affect reaction rates

chemical nature, physical states, temperature, concentration, and catalysts

Physical states increase the reaction rate as you go from

solid to liquid to gas - because you are increasing surface area

As you increase temperature, you increase rate because

there more kinetic energy and therefore more collisions

What is a catalyst?

A substance that increase a reaction rate but it is not consumed

The rate constant K is influenced by

temperature

The rate constant k is NOT influenced by

concentrations

Zero order units

M/s

First order units

1/s

Second order units

1/(M s)

Third order units

M^-2 s^-1

How much faster will the rate be if the concentration of OH^- (aq) is quadrupled?

4 times faster

What would happen if you increased the temperature of this reaction by 100K?

Rate increases

Use the integrated rate law when:

• when given concentration vs. time data.

• to calculate concentrations at a specific time.

• to determine half-life or how long it takes for something to decay or react.

Use rate law when:

• when working with initial rates.

• to find the order of the reaction

• find the rate constant (k) from how rate changes, not time.

First order plot slope

negative (-K)

First order plot

ln[A] and time

Second order plot

1/[A] and time

Second order slope

positive (K)

Zero order plot

[A] and time

Zero order slope

negative (-K)

All graphs must be

linear (a super straight line)

Slope = -K

K = -slope

Zero order rate law looks like:

rate = k

Collision theory 3 main points:

• Rate of reaction is proportional to the rate of reactant collisions

• Collisions need to be in the correct orientation

• Collisions need enough energy to react

If you increase temperature

kinetic energy increases as well

A is the frequency factor, does it change with temperature?

no it doesn’t change, and units match k

y = mx + b m = what? b = what?

m = slope = -Ea/R b = ln A

Whats the Arrhenius equation?

k = Ae^-(Ea/RT)

What should the units for Ea be?

J/mol

Activation energy ________ impacts rate

greatly

Intermediates are

chemical species produced in one step of a reaction mechanism and then used in another

Transition states are different than intermediates because:

• non-isoluble

• never part of rate law

• energy high

Intermediates are different from transition states because:

• Isolute

• In elementary steps of rate laws

• energy lows

Bimolecular

involves two molecules colliding and reacting to form products

unimolecular

involves one molecule reacting to form products

Termolecular

involves three molecules colliding and reacting to form products (very rare)

The ______ step controls the overall rate

slow

Which steps are always reversible?

fast steps