Chemistry II Exam II

Rate of reaction

change in amount of a reactant or product per unit time

Rate expression

Math representation of rate of reaction

Rate of a reaction is equal to

rate of change of a reactant/product divided by its coefficient

Are products positive or negative in rates of expression?

positive

Are reactants positive or negative in rates of expression?

negative

Average reaction rate

rate at which reactions proceeds over a period of time

Initial reaction rate

rate at which a reaction is proceeding at a specific time

Instantaneous Reaction Rate

the rate at which a reaction is proceeding at a specific time

As you move down a group, the alkali metals react at a faster or slower rate with water?

faster

What number tells the order of a rate law?

The exponent

Are reactants the only thing in a rate law?

yes

m is order with respect to

A

n is oder with respect to

B

What do you add to find the overall order?

m and n

First order reaction equation

rate=k[a]

Integration with respect to time first order equation

ln [A]0/[a]t = kt

First order reaction equation in slope equation form

ln[a]= -kt + ln[a]0

Zero order has a positive or negative slope?

negative

First order has a positive or negative slope?

negative

Second order has a positive or negative slope?

positive

Zero order plot of concentration vs time

[A] vs time

First order plot of concentration vs time

ln[A]

Second order plot of concentration vs time

1/[A]

Integrated rate law for zero order

[A]t= -kt + [A]0

Integrated rate law for second order

1/[A]t= kt + 1/[A]0

Half-life definition

time it takes for half of the reacant amount to be consumed

Half-life equation

[A]t = ½ [A]0

Half-life equation for first order

t1/2= 0.693/k

Units for 0 order reaction

m/s

Units for first order reaction

s^-1

Units for second order reaction

m^-1/s^-1

Collision Theory

Reactants must collide in order to react with each other

Rate of reaction is proportional to

rate of reactant collisions

Increasing the temp often leads to an increase or decrease in rate of reaction?

increase

Temperature increases the average what of reactants?

Kinetic energy

Arrhenius Equation

k= Ae^ -Ea/RT

The lower the Ea, the faster or slower the reaction?

Faster

Catalyst only effects

activation energy

Catalyst definition

Substance that can increase the reaction rate without being used up in the reaction

Intermediates definition

Species that are produced in one step and consumed in a subsequent step

Why is activation energy changed by adding a catalyst?

The catalyst changes the reaction mechanism

At equilibrium, the amount of reactants and products

stops changing

Equilibrium equation

k= products/reactants

Are solids and liquids included in equilibrium expressions?

no

The reaction will reach equilibrium when most of the reactant turns into a product

large k

The reaction will reach equilibrium after very little reactant has been converted to product

small k

If Qc=Kc

reaction is at equilibrium

If Qc is less than Kc

the reaction proceeds in the forward direction

If Qc is greater than Kc

the reaction proceeds in the reverse direction

Le Chatelier’s principle

When a chemical system at equilibrium is disturbed, it returns to equilibrium by counteracting the disturbance

Do liquids and solids have an effect on Le Chatelier’s principle

no

Four factors that affect rate of a reaction

concentration, temperature, surface area of a solid reactant, and catalysts

If heat is a product

k decreases

If heat is a reactant

k increases

The reaction rate of a 60 degree reaction will be greater than at 30 degrees because

there is a greater proportion of reactants with the necessary kinetic energy to react

What could decrease the rate of a reaction?

decreasing the surface area

At equilibrium what is equal to the rate of the reverse reaction?

the rate of the forward reaction

Does the magnitude of k indicate how rapidly or slowly equilibrium will be reached?

no

What is the order of the reaction when a graph of ln[a] vs. time gives a straight line with a negative slope?

first

What order of reaction has a linear curve when plotting concentration vs time

zero

What is the effect on k as the activation energy for a reaction increases?

it decreases

An increase in the temperature would result in an increase in the value of the

rate constant

The molecularity of an elementary step is determined by

how many reactants are involved in the reaction

To determine the rate law for a mechanism containing the equilibrium step, you must redefine

the intermediate in terms of the equilibrium step

Can you have any intermediates in the rate law?

no

Catalysts increase reaction rates by

providing an alternate reaction mechanism with a lower activation energy

Another way to describe a species that slows down the reaction rate is

as an inhibitor