How Fast

Question 1

What are factors effecting rate?

Answer 1

Temp
Conc
SA
Catalyst

Question 2

What is rate of reaction?

Answer 2

Change in conc of a reactant (or product) per unit time.

How quickly reactants are used up/ products formed

Question 3

What is average rate?

Answer 3

Total change in conc of reactants (or products) divided by the time taken for the reaction to take place

Question 4

What is instantaneous rate?

Answer 4

A reaction rate of change occurring at a specific time in the reaction

Question 5

What is the rate of reaction equation?

Answer 5

Change in conc
———————— Units: moldm-3s-1
Time

Question 6

What are the common reaction orders?

Answer 6

Zero
First
Second

Question 7

What is zero order?

Answer 7

When the conc of a reactant has no effect on rate

Question 8

What is first order?

Answer 8

When the rate depends on its concentrations raised to the power of one

Question 9

What is second order?

Answer 9

When the rate depends on its conc raised to the power of two

Question 10

What is the rate equation?

Answer 10

Rate = K[A] ^x [B]^y

Question 11

Give examples of methods that continuously monitor conc

Answer 11

Change in mass
Inverted measuring cylinder
Gas syringe
pH changes - using probe/ data logger
Colorimetry - measure absorbance of reaction

Question 12

What does the graph look like for zero order?

Conc-time graph

Answer 12

Produces straight line with negative gradient

Reaction rate does not change

Question 13

What does the graph look like for first order?

Conc-time graph

Answer 13

Downward curve with decreasing gradient over time

As gradient decreases with time, reaction slows down

Question 14

What does the graph look like for second order?

Conc-time graph

Answer 14

Downward curve but steeper at the start, tailing off more slowly

Question 15

How can we tell if it is a first or second order conc-time graph?

Answer 15

Use half life

Fist order will have a constant half life (take same amount of time each at each half)

Question 16

What is a method for measuring initial rate (conc)?

Answer 16

Clock method

Question 17

What does the graph look like for zero order?

Rate-conc graph

Answer 17

Straight line - horizontal

Question 18

What does the graph look like for first order?

Rate-conc graph

Answer 18

Straight line through the origin - diagonal

Question 19

What does the graph look like for second order?

Rate-conc graph

Answer 19

Upwards curve with increasing gradient

Question 20

What does the graph for zero order show?

Rate-conc graph

Answer 20

Rate doesn’t change

Question 21

What does the graph for first order show?

Rate-conc graph

Answer 21

Rate directly proportional to conc

Question 22

Why can’t you work out K from the second order rate-conc graph?

Answer 22

Because curve doesn’t acc confirm its 2nd. just its not 0 or 1

Question 23

What must you do to work out K from 2nd order rate-conc graph?

Answer 23

Use results from graph to plot second graph
But plot rate against [A]^2
Then find K through line gradient
Should be straight line

Question 24

What is a reaction mechanism?

Answer 24

Describes one or more steps involved in a reaction in a way which makes it clear how certain bonds are broken and made

Question 25

What is the rate determining step?

Answer 25

The overall rate of reaction (the one you could measure if you did an experiment) is controlled by the rate of the slowest step. The slowest step is called the R.D.S

Question 26

What does the rate expression tell us?

Answer 26

If the species is in the rate equation it is in the R.D.S If it is not in the rate equation it is not in the R.D.S The power of the substance is the number of the substance in the equation

Question 27

What must the steps involved in the reaction add up to?

Answer 27

The overall chemical equation in the reaction | eg. some compounds/elements cancel out to make overall equation

Question 28

Which step is the R.D.S?

Answer 28

Always the slowest

Question 29

What is the Arrhenius equation?

Answer 29

K = Ae ^ -Ea/RT

Question 30

What is e^ -Ea/RT?

Answer 30

Represents proportion of particles that exceed Ea and have sufficient energy to take place

Question 31

What is A? | Arrhenius equation

Answer 31

Takes in account the frequency of collisions with correct orientation Increases slightly with temp but overall constant

Question 32

What happens to the rate constant in the Arrhenius equation when you increase temp?

Answer 32

The rate constant increases and so does rate

Question 33

What happens to the rate constant in the Arrhenius equation when you use a catalyst?

Answer 33

Decreases Ea so increases rate constant and so increases rate

Question 34

What is the more effect caused by when you increase temp in Arrhenius equation?

Answer 34

Caused by more particles exceeding Ea than increased collisions

Question 35

When can't you extrapolate the graph?

Answer 35

When the scale is broken

Question 36

What is the inverse of Arrhenius equation?

Answer 36

Ln K = -Ea/R X 1/T + Ln A

Question 37

How do you use the inverse of Arrhenius equation calculate

Answer 37

``` 1. Work out Ln K and 1/T 1/ first column no. Ln(2nd column no.) 2. Plot graph - Ln K against 1/T 3. Workout gradient 4. Calculate A from y-intercept Extrapolate line ```

Question 38

How do you find Ea from the gradient?

Answer 38

-Ea/R = X -Ea = 8.31x Ea = -8.31

Question 39

How do you find A when you can't extrapolate the graph?

Answer 39

Use Ln K = -Ea/R X 1/T + Ln A Rearrange to get Ln A Then A = E^ Ln A