5.1.1 - How fast

Question 1

Define the term rate of reaction.

Answer 1

The change in concentration of a reactant (or product) per unit time
Its usual unit is mol dm^-3 s^-1

Question 2

Define the term overall order.

Answer 2

The sum of the powers of the concentration terms on the rate equation.

Question 3

Define the term order of a reaction (with respect to a given reactant).

Answer 3

The power to which the concentrations of the reactants is raised in the rate equation.

Question 4

Define the term rate constant.

Answer 4

A constant value that relates the rate of a reaction at a given temperature
to the concentrations of the reactants. For a first order reaction, this can be determined using
the relationship k = ln 2/t 1/2

Question 5

Define the term half-life.

Answer 5

The time taken for the concentration of a reactant to half.

Question 6

Define the term rate-determine step.

Answer 6

The slowest step of a reaction.

Question 7

Write a general rate equation and label what each part means.

Answer 7

Question 8

What does zero order mean ?

Answer 8

Changes in concentration has no effects on the rate.

Question 9

What does first order mean ?

Answer 9

Changes in concentration has a proportional change on rate=
E.g if [A] doubles then rate doubles

Question 10

What does second order mean ?

Answer 10

Changes in concentration has a squared proportional change on rate.
E.g if [A] doubles then rate quadruples.

Question 11

Key note for orders.

Answer 11

Orders can only be determined from experimental data. You can’t work the out just by looking at an equation.

Question 12

What do you understand about the effects of :
- Temperature
- Concentration
- Pressure
On the rate constant (K)

Answer 12

• Temperature : As temp increases so does the rate constant. As temp decrease the rate constant also decreases. Think of it like Rate of reaction and K are proportional, if the rate of reaction increases or decreases due to temp so will the rate constant (K).
• Concentration : No effects just like in Kp and Kc.
• Pressure : No effects just like in Kp and Kc.

Question 13

Oddly worded question but if the value of K is larger then what is the effect on the rate of reaction.

Answer 13

• The rate of reaction would be faster if the value of ‘K’ is larger. Remember this for multiple choice questions.

Question 14

What is the units for rate

Answer 14

mol dm^-3 s^-1

Question 15

How do we calculate the rate constant in terms of rate and concentration ?

Answer 15

Just rearrange the normal rate equation. To make K the subject

Question 16

When a reactant has 0 order do we include them in the rate equation ?

Answer 16

No, because they have no effect on the rate so will not be included.
If you do then just remember to put 0 as their power (The rate value will end up being the same value if you didn’t include them at all)

Question 17

How do we calculate the rate of reaction from a graph ?

Answer 17

Draw a tangent ( if needed) and calculate the gradient.

Question 18

Blurt everything you understand about the initial rates method (allery chem 34.12)

Answer 18

Doing several experiments where the initial rate is measured and the initial concentration of a reagent is changed (initial rates method), with all other concentrations kept constant.

Question 19

Blurt everything you understand about the continuous rates experiment.

Answer 19

Remember : The other reagents must be in a large excess so they are effectively constant.

Question 20

How would zero order look on a concentration-time graph

Answer 20

Question 21

How would first order look on a concentration-time graph

Answer 21

Question 22

How would second order look on a concentration-time graph

Answer 22

Question 23

How can we distinguish between a first and second order graph.

Answer 23

Calculate the half life.
1st order = Half life is constant
2nd order = half life increases by roughly the same amount.

Question 24

How would zero order look on a rate-concentration graph.

Answer 24

This explains zero order because changing concentration does not effect the rate of the reaction.

Question 25

How would first order look on a rate-concentration graph.

Answer 25

This explains first order because the change in concentration is directly proportional to the rate. So changing the concentration changes the rate equally.

Question 26

How would second order look on a rate-concentration graph.

Answer 26

This quadratic graph represents a second-order reaction, where the rate is proportional to the square of the concentration. This means that if the concentration doubles, the rate increases by a factor of four. The curved shape of the graph shows that as concentration increases, the rate increases more rapidly. This follows the rate equation: Rate = k[Concentration]².

Question 27

Another oddly worded question but how does the concentration-time graph help with the rate-concentration graph.

Answer 27

To find the rate (for the rate-concentration graph) we need to uses the concentration-time graph to find the gradient (we can do this by drawing a tangent if needed).

Question 28

Define the term half life ?

Answer 28

The time it takes for the concentration of the reactant to half.

Question 29

What do we use half life to calculate ?

Answer 29

The rate constant (K) units = S^-1

Question 30

How do we calculate the rate constant using half life ?

Answer 30

symbol for half life **t_1/2**

Question 31

How would the rate-concentration graph look like with all the combined orders.

Answer 31

Question 32

Using experimental data to work out the rate equation (step 4 ) and 41.22 allery chem

Answer 32

This is more practice than explains btw tho

Question 33

Using experimental data to work out the rate equation when all the concentrations for one reactant is different(step 4 ) and 47.02 allery chem

Answer 33

Again more practice and less explanation.

Question 34

Using experimental data to filling gaps in a table. (Step 4) and 44.43 allery chem

Answer 34

Again this is more practice than explanation.

Question 35

If a reaction mechanism has a series of steps, then the overall rate is dependent on ?

Answer 35

**The rate of the slowest step** (RDS)

Question 36

Constructing overall equations and rate equations from a series of mechanics (section 5) and 53.00 allery chem

Answer 36

Again more practice and less explanation.

Question 37

Arrhenius - Using y=mx + c what would each component of this equation represent in the Arrhenius equation

Answer 37

Question 38

Arrhenius equation

Answer 38

Question 39

Answer 39

Question 40

Rearrange the Arrhenius equation to make **K** the subject

Answer 40

Question 41

Rearrange the Arrhenius equation to make **E_a** the subject

Answer 41

Question 42

Rearrange the Arrhenius equation to make **A** the subject

Answer 42

Question 43

Rearrange the Arrhenius equation to make **T** the subject

Answer 43

Question 44

What happens to the rate constant as the activation energy decreases (gets smaller)

Answer 44

Question 45

What happens to the rate constant as the temperature increases

Answer 45

Question 46

How do we get rid of the ‘e’ part (the exponential next to the A in the Arrhenius equation)

Answer 46

Question 47

How do we us a graph to calculate the Arrhenius constant ?

Answer 47