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A-level Chemistry > Module 5: How Fast? V1 > Flashcards

Module 5: How Fast? V1 Flashcards

1
Q

How could you follow the rate of the following reaction? Include the apparatus.

A

Measure decreasing light absorbance as orange Br2 decolourises using a colorimeter ✓

Measure the decreasing pH due to increasing H+ and Br- ions using a pH meter ✓

Measure increasing conductivity due to more H+ and Br- ions using a conductivity meter ✓

Measure the increasing volume of CO2 gas produced using a gas syringe ✓

Measure the decreasing mass of the solution until constant mass using a balance ✓

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2
Q

Define what is meant by a “Reaction order”

A

How the rate of reaction will be affected if the reactant’s concentration is changed ✓

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3
Q

Define what is meant by:

zero order

first order

second order

A

Zero order: The rate is unaffected by any changes in concentration. ✓

First order: The rate changes the same as the change in concentration. ✓

Second order: The rate changes by the square of the change in concentration. ✓

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4
Q

Sketch a concentration-time graph, with labelled axis, for a 0, 1st and 2nd order concentration-graph

State a key feature for each one

A
✓✓✓
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5
Q

Sketch a rate-concentration graph, with labelled axis, for a 0, 1st and 2nd order concentration-graph

State a key feature for each one

A
✓✓✓
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6
Q

Define what is meant by “half-life” and with which order can calculate a value for the rate constant for

A

The half-life (t1/2) of a reactant is the time taken for its concentration to halve ✓

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7
Q

For reactant A, the concentration-time graph has a constant half-life. For reactant B, the rate-concentration graph is a horizontal line.
Determine the order for reactants A and B.

A
✓
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8
Q

For reactant C, the concentration-time graph has a constant gradient. For reactant D, the rate-concentration graph also has a constant gradient with the line passing through the origin.
Determine the order for reactants C and D.

A
✓
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9
Q

Show that the order is 2 wrt [A] and 0 wrt to [B].

A

In experiments 1 and 2, [A] X2 whilst [B] is constant and rate X4. ✓
2nd order wrt [A] ✓

In experiments 2 and 3, [B] X2 whilst [A] is constant and rate does not change. ✓
0 wrt [B] ✓

Overall order is 2nd + 0 = 2nd order ✓

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10
Q

The following data was obtained for the bromine clock reaction.
i) Determine the order with respect to Br -.
(ii) Determine the order with respect to BrO3-.
(iii) Determine the order with respect to H+.
(iv) Determine the overall order.

A

i) 1 ✓
(ii) 1 ✓
(iii) 2 ✓
(iv) 4 ✓

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11
Q

For a reaction involving the reactants A, B and C where the order is 2, 1 and 0 respectively.
Give the rate equation
State the overall order
Rearrange the rate equation for k and work out its units.

A
✓✓✓
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12
Q
A
✓✓
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13
Q
A

Order 2 ✓

Look at the units. The order is based on what the units of the rate constant is.

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14
Q

A reaction is first order with respect to a reactantX.

Which rate–concentration graph for reactantXis the correct shape?

A

A ✓

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15
Q

A reaction is zero order with respect to a reactantA.

Which concentration–time graph for reactantAis the correct shape?

A

A ✓

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16
Q
A

20 minutes ✓

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17
Q
A
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18
Q

Find the order for the reactants A, B, C & D
i) [A] x2 and rate x2, order wrt [A] is…

ii). [B] x2 and rate does not change, order wrt [B] is…

iii) [C] x3 and rate x9, order wrt [C] is…

iv) [D] x3 and [A] x3, rate x9, order wrt [D] is…

A

i) First ✓
ii) Zero ✓
iii) Second ✓
iv) First ✓

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19
Q
A
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20
Q
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21
Q
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22
Q
A
23
Q
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24
Q
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25
Q
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26
Q

The half-life of a first order reaction is 300 seconds.

Calculate the rate constant for the reaction and give its units.

A
27
Q

Describe the initial rates method

A

Start by mixing equal amounts of each solution and find the rate of reaction. ✓

Repeat the experiment, diluting each solution in turn with distilled water. ✓

Change the concentration of only one solution at a time. ✓

Keep the total volume the same for each experiment. ✓

Put the results in a table and check how changing the concentration affects the rate of reaction. ✓

28
Q

State what happens to the rate constant k, as temperature increases.

Include a sketch of a graph in your answer

A

Increases ✓

29
Q
A
30
Q
A
31
Q

State the effect on k and hence the rate of reaction if the following are increased:

If the pre-exponential factor increases

If activation energy increases

If temperature increases

A

If the pre-exponential factor increases, k increases

If activation energy increases, k decreases

If temperature increases, k increases

32
Q

In the Arrhenius equation, state what each term, stands for in terms of y=mx+c

A

y - y coordiantes = ln(k)

x - x coordiantes = ln(A)

c - y Intercept = ln⁡A

m - Gradient = -Ea/R

33
Q

Activation energy in the Arrhenius equation is always given and used in what unit?

A
✓
34
Q

The rate determining step for a reaction between X and Y is given as 2 X → Z.

Predict the rate equation for this reaction.

A
35
Q

Define what is meant by the “rate of reaction”

A

change in concentration of reactant or product per unit time for the change to take place ✓

36
Q

Describe how you would draw a rate-concentration graph

A

Use the continuous monitoring method as for determining a concentration-time graph ✓

Find the rate (from the gradient) at various points along the concentration-time curve ✓

You would then plot a rate-concentration graph ✓

37
Q

For reactant A, the concentration-time graph has a constant half-life. For reactant B, the rate-concentration graph is a horizontal line. Determine the

A

A: First order ✓

B: Zero order ✓

38
Q

For reactant C, the concentration-time graph has a constant gradient. For reactant D, the rate-concentration graph also has a constant gradient with the line passing through the origin. Determine the order for reactants C and D.

A

c: Zero order ✓

B: First order ✓

39
Q

Define what is meant by the “Rate determining step”

A

Slowest step in the reaction mechanism ✓

40
Q

A reaction can be shown as being first order wrt [H+] by continuous monitoring

State how you would use the graph to show this first order relationship

A

Calculate multiple half-lifes ✓

Constant half life shows first order ✓

41
Q
A

There would be a x125 increase in rate ✓

42
Q

If you were to follow the reaction by measuring the mass lost, how would you know the reaction had gone to completion?

A

Weigh to constant mass ✓

43
Q

What apparatus would you use to follow a reaction with a colour change?

A

Colorimeter ✓

44
Q

What effect does an increase in pressure have on the reaction rate and rate constant

A

Rate of reaction increases and rate constant k increases ✓

There are more molecules per unit volume ✓

There are more frequent collisions ✓

45
Q

What effect does a decrease in volume have on the reaction rate and rate constant

A

Pressure decreases, rate of reaction increases and rate constant k increases ✓

There are more molecules per unit volume ✓

There are more frequent collisions ✓

46
Q

What effect does an increase in temperature have on the reaction rate and rate constant

A

Rate of reaction increases and rate constant k increases ✓

More molecules have energy above the activation energy ✓

There are more frequent collisions ✓

47
Q

In rates experiment, a student is trying to find out the order wrt [Y]

In the reaction, X reacts with Y.

He thinks that both reactants are first order, wrt to [X] and [Y]

How can the student modify the experiment to show that the reaction is first order wrt [Y]

A

Use a large excess of [X] ✓

So its concentration is kept constant and monitor [Y] against time ✓

48
Q
A

20 minutes ✓

First order, so half life is constant

49
Q
A
50
Q
A

+37.6 ✓

Remember to convert from J to kJ

51
Q
A
52
Q
A

A-level Chemistry (15 decks)

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