5.1.1 How Fast?

Question 1

Define rate the rate of reaction?

Answer 1

Change in concentration of a reactant or product per unit time

Question 2

How is the rate of reaction calculated?

Answer 2

Change in concentration of reactants or products/ time

Question 3

What does it mean when the order is zero with respect to the reactants?

Answer 3

Changing concentration of the reactant has no effect on the rate

Question 4

Describe what is meant when the order of reaction is first order?

Answer 4

Rate is directly proportional to concentration

Question 5

What is meant when a reaction has a second order of reaction?

Answer 5

Change in rate = change in concentration is squared

Question 6

What is the generalised rate equation and what does each term mean?

Answer 6

Rate = k [X]^m [Y]^n

K= rate constant doe equation

[X] & [Y] = concentration of reactants

M & n= orders respect to X & Y

Question 7

Does zero order appear on the reactants in the rate equation?

Answer 7

No because they don’t have an effect on the rate

Question 8

How do you calculate overall order of a reaction?

Answer 8

Sum of individuals orders

Question 9

How are the units of the rate constant calculated?

Answer 9

• unit of rate= mol dm^-3 S^-1
• units of concerntration= mol dm^ -3

Rearrange rate equation to get k= sub units and cancel them

Question 10

How could you measure the rate of reaction experimentally?

Answer 10

• use a colorimeter at suitable intervals if there is a colour change

-if gas is evolved use a gas syringe to collect volume of gas evolved, or measure the change in mass of the reaction mixture

Question 11

What does half life mean?

Answer 11

Time taken for concentration of a reactant to decrease by half

Question 12

What is the symbol for half life?

Answer 12

t 1/2

Question 13

What does a concentration time graph for a zero order reactant?

Answer 13

Line is a straight line going in a downward direction

Question 14

What does a concentration time graph for first order reactant look like?

Answer 14

Curved line in a downwards direction

Question 15

Describe the relationship between first order reactions and half life?

Answer 15

Have constant half life’s

Question 16

What is the equation that is used to determine rate constant using half life in a first order reaction?

Answer 16

K= In2 / t 1/2

Question 17

What is the relationship between rate and time?

Answer 17

Rate ♾️ 1/ t

Question 18

What does a rate concentration graph for a zero order reactant look like?

Answer 18

Constant graph

Question 19

Draw a rate concerntration graph for a first order reactant?

Answer 19

Increasing Straight line

Question 20

What does a rate conerntration graph look like for a second order reaction?

Answer 20

Curved increasing line

Question 21

How do you determine the rate constant from a rate concentration graph of first order?

Answer 21

K = rate / concentration

Question 22

What is the rate determining step?

Answer 22

The slowest step in a reaction with multiple steps

Question 23

How does the rate determining step link to the species involved in the rate equation?

Answer 23

-Any species involved in the rate determining step appear in the rate equation

-species only involved after the rate determining step do not appear in the rate equation

Question 24

For a reactant in the rate equation, what indicates how many molecules of that reactant are involved in the rate determining step?

Answer 24

Order of reactant

Question 25

What affects the value the rate constant for a given reaction?

Answer 25

Temperature

Question 26

What is the Arrhenius equation and describe each term?

Answer 26

K = Ae -Ea/ RT

K= rate constant for reaction
A= number of collisions between reactant molecules
e= mathematical quantity
R= gas constant
T= temperature in kelvin
Ea= activation energy in joules

Question 27

How can you convert Arrhenius equation into a useful form for plotting a graph?

Answer 27

InK= -Ea/RT + In A

Graph of ink against 1/T is a straight line

Gradient= -Ea / R and y intercept is InA

Question 28

How do you calculate activation energy (Ea) from a graph?

Answer 28

= - gradient X 8.314

Question 29

How do you calculate A?

Answer 29

e^ intercept

Question 30

What does the rate equation tell us about the rate determining step?

Answer 30

• the reactants involved in the rate determining step

-the number of each reactant involved from the order