Kinetics - Chapter 5 and 18

Question 1

What is needed for a reaction to be successful

Answer 1

particles must collide with enough energy and in correct orientation

Question 2

What is activation energy

Answer 2

the minimum amount of energy needed to start a reaction is called the activation energy

Question 3

What happens to a reaction when the activation energy is reduced

Answer 3

faster reaction

Question 4

What is the Maxwell-Boltzmann distribution graph

Answer 4

Graph with energy on the x axis and number of particles on the y axis

Area under the curve is the total number of particles

The peak is the most probable energy

The average energy is just to the right of the peak

Question 5

What is the rate of a reaction

Answer 5

It is the change in concentration of a substance per unit of time

Question 6

What factors affect rate

Answer 6

Concentration (pressure)
Surface area
Temperature
Catalyst

Question 7

What happens to the rate when concentration is increased

Answer 7

Rate increases

More particles in a given volume so more frequent successful collisions will happen

Question 8

What happens to the rate when surface area is increased

Answer 8

Rate increases

Because particles of a solid are exposed so more chance of a successful collision with other reactant particles

Question 9

What happens to the rate when temperature is increased

Answer 9

Rate increases

Particles moves faster so collide more often

Many more particles with energy bigger than activation energy

Question 10

What happens when a catalyst is added

Answer 10

Rate increases

Catalysts provide an alternative reaction pathway with a lower activation energy so more particles have energy above activation energy

Question 11

How does concentration affect rate

Answer 11

The rate depends on the concentration of the reactants but not all reactants make the same contribution to how fast a reaction goes

Question 12

What is a rate equation

Answer 12

It is an equation used to show how the rate of a reaction depends on the concentration of the reactants involved

rate = k [A]x [B]y

Question 13

What is the order of the reaction

Answer 13

The sum of the orders of reaction of each substance

Question 14

How do you determine the rate equation for a reaction

Answer 14

You need to determine the orders with respect to each of the reactants

Question 15

What methods are used to find the rate equation

Answer 15

Initial Rate Method
Graphical method

Question 16

What is the initial rate method

Answer 16

It is when the rates are compared from a series of experiments in which the concentration of only one reactant is varied at a time

Question 17

What is the graphical method

Answer 17

It is when an experiment is carried out where each reactant varies with time and plot concentration-time graph
The shape indicates the order of each reactant

A second graph is then plotted of rate-concentration by measuring the gradient at different points on the first graph

Question 18

What is zero order for the graphical method

Answer 18

A straight line with a negative gradient for conc-time graph

A horizontal flat line for conc-rate graph

Question 19

What is first order for the graphical method

Answer 19

A sloping curve which drops with a constant half-life for conc-time graph

A straight positively sloped line for conc-rate graph

Question 20

What is second order for the graphical method

Answer 20

The line declines steeply then flattens out for conc-time graph

The line is curved for the conc-rate graph

Straight line for conc2 - rate graph

Question 21

What happens to the Maxwell-Boltzmann distribution graph when temperature increases

Answer 21

Peak shifts to the right and down
The bit after goes up

Question 22

What is the rate constant

Answer 22

It is the value of the rate at any particular temperature when the concentration of all species in the rate equation are 1 mol dm-3

Question 23

What is the Arrhenieus equation

Answer 23

k = Ae -Ea/RT

lnk = -Ea/RT + ln A

Question 24

What graph do you plot for an Arrhenius plot

Answer 24

1/T on the x axis
ln k on the y axis

Gradient is -Ea/R
y intercept is ln A

Question 25

What is the rate determining step

Answer 25

It is the slowest step in a reaction mechanism and controls the overall rate of the whole reaction

Question 26

What is in the rate equation

Answer 26

species that are involved before or during the the rate determining step

Question 27

What is assumed about the order with respect to a particular reactant

Answer 27

That it shows the number of particles of it participating before or during the rate determining step

Question 28

What does it mean for a reactant if it is zero order with the rate determining step

Answer 28

The species is present only after the rate determining step

Question 29

For primary haloalkanes what is the rate equation for the hydrolysis of haloalkanes

Answer 29

rate = k [RX] [OH-]

Question 30

What is the rate equation for the hydrolysis of tertiary haloalkanes

Answer 30

rate = k [RX]

Question 31

Why does using a large amount of reactant take them out the rate equation

Answer 31

Because the concentration is almost constant making them zero order