Rates of Chemical Reactions

Question 1

Average rate

Answer 1

The average change in the concentration of a reactant or product over time.

Question 2

Instantaneous rate

Answer 2

The rate of the reaction at a particular time

Question 3

How do you find the instantaneous rate using a concentration-time graph?

Answer 3

Draw a tangent line to the curve and find the slope of the tangent

Question 4

How do you represent the rate of a reaction?

Answer 4

1. in terms of the disappearance of reactants
2. in terms of the production of products

Question 5

Why is the change in concentration is always negative?

Answer 5

The concentration of a reactant always decreases as a reaction progresses

Question 6

What are 3 methods for measuring reaction rates

Answer 6

1. Monitoring mass, pH, and conductivity
2. Monitoring pressure & volume
3. Monitoring colour

Question 7

What factors affect reaction rate?

Answer 7

Increase in temperature, increase in concentration, a catalyst, increasing the surface area of a reactant, or what a specific reactant is.

Question 8

What is a rate law equation?

Answer 8

An expression that describes the relationship between the rate of a chemical reaction and the concentration of its reactants.

Question 9

Chemists carry out experiments to determine the rate law equation for a given reaction at
_______________.

Answer 9

a given temperature.

Question 10

What does the rate constant (k) do?

Answer 10

Indicates the speed of a reaction and stays the same throughout the reaction.

Question 11

Why is a first order reaction zero order in water?

Answer 11

The rate of the reaction does not depend, at all, on the
concentration of water.

Question 12

How do you determine the overall reaction order?

Answer 12

Add the coefficients (m +n)

Question 13

What is the initial rates method?

Answer 13

Measuring and comparing the initial rate of each reaction

Question 14

What does the initial rates method do?

Answer 14

Allows the values of reaction orders to be found by conducting multiple experiments under controlled conditions and measuring the rate of the reaction in each case

Question 15

What is half-life (t1/2)?

Answer 15

the time that is needed for the reactant mass or
concentration to decrease by one half of its initial value

Question 16

What is collision theory?

Answer 16

In order for a reaction to occur, reacting particles must collide with one another.

Question 17

How does concentration affect reaction rate?

Answer 17

More reactant particles in a given concentrated volume
increase the number of collisions.

Question 18

How does the surface area of reactants affect reaction rate?

Answer 18

Only atoms or ions at the surface of a solid reactant
can interact with other reactants, thus, increasing the surface area of a solid reactant in effect increases
its concentration.

Question 19

How does the pressure of reactants affect reaction rate?

Answer 19

Pressure increases cause reactant particles to collide more frequently with the walls of the container and with
each other.

Question 20

How does the temperature of reactants affect reaction rate?

Answer 20

The rate of a chemical reaction increases exponentially
when the average kinetic energy is increased, so a small increase in temperature has a
very large effect on the rate.

Question 21

How does a catalyst with reactants affect reaction rate?

Answer 21

A catalyst provides an alternative route for the reaction. Lowers activation energy.

Question 22

What is an effective collision, and what criteria must it satisfy?

Answer 22

An effective collision is one that results in the formation of products. It must satisfy correct orientation of reactants and sufficient collision energy.

Question 23

What is correct collision geometry?

Answer 23

When particles collide with the proper orientation relative to one another in order for new bonds to form.

Question 24

Temperature is a measure of ___________ of the particles in a substance.

Answer 24

the average kinetic energy

Question 25

What is a Maxwell-Boltzmann distribution?

Answer 25

A description of the distribution of the energies of the molecules in a classical gas.

Question 26

What does transition state theory do?

Answer 26

Examines the transition from reactants to products.

Question 27

What is a potential energy diagram?

Answer 27

A diagram that charts the potential energy of a reaction
against the progress of the reaction.

Question 28

What is the activated complex?

Answer 28

The chemical species that exists at the transition
state.

Question 29

What is the transition state?

Answer 29

The change-over point of the reaction.

Question 30

What is a reaction mechanism?

Answer 30

a series of steps that make up an overall reaction.

Question 31

What is an elementary reaction?

Answer 31

A step in a reaction mechanism. It may involve the formation of different molecules, or a change in the energy or geometry of the starting molecules.

Question 32

What is a reaction intermediate?

Answer 32

Molecules formed in an elementary reaction and consumed in a subsequent elementary reaction

Question 33

Why are elementary reactions the exception to the rule that says rate law cannot be determined by looking at the chemical equation?

Answer 33

The exponents in the rate laws of elementary equations are the same as the stoichiometric coefficients for each reactant.

Question 34

What is the rate-determining step?

Answer 34

The slowest elementary reaction in a mechanism.

Question 35

A catalyzed reaction consists of a ______ mechanism

Answer 35

two-step

Question 36

What is the difference between a homogeneous catalyst and a heterogeneous catalyst?

Answer 36

Homogeneous catalysts exist in the same phase as the reactants. Heterogeneous catalysts exist in a phase different from the phase of the reaction
it catalyzes