Module 5.1

Question 1

Define rate of reaction

Answer 1

The change in concentration of a reactant or product per unit of time

Question 2

List ways in which we can measure the rate of reaction?

Answer 2

Measure the loss in mass
Measure how fast a gas in produced 
Measure how long it takes for a solution to go cloudy
Measure the pH change of a reaction
Watch for colour change

Question 3

When measuring a change in mass, what should you use?

Answer 3

A weighting scale

Question 4

When measuring how fast a gas is produced, what should you use?

Answer 4

A gas syringe

Question 5

When measuring how long it takes for colour change, what should you use?

Answer 5

Colourimetry

Question 6

What is meant by order?

Answer 6

With respect to a reactant, the order is the power to which the concentration of a reactant is raised to in the rate equation

Question 7

What 3 orders must we be aware of?

Answer 7

Zero order
First order
Second order

Question 8

What does the concentration-time graph of a zero order reactant look like?

Answer 8

Straight line downards

Question 9

What does the rate-concentration graph of a zero order reactant look like?

Answer 9

Straight line

Question 10

With zero order reactants, what will happen to the rate, if the concentration of the reactant is changed?

Answer 10

Nothing

Question 11

With zero order reactants, what pattern does its half-life follow?

Answer 11

DECREASES with time

Question 12

What does the concentration-time graph of a first order reactant look like?

Answer 12

Slopes downwards

Question 13

What does the rate-concentration graph of a first order reactant look like?

Answer 13

Straight line upwards

Question 14

With first order reactants, what will happen to the rate, if the concentration of the reactant is changed?

Answer 14

The rate changes by a proportionally equal amount

Question 15

With first order reactants, what pattern does its half-life follow?

Answer 15

Constant

Question 16

What does the concentration-time graph of a second order reactant look like?

Answer 16

Slopes downwards

Question 17

What does the rate-concentration graph of a second order reactant look like?

Answer 17

Slopes upwards (exponential growth)

Question 18

With second order reactants, what will happen to the rate, if the concentration of the reactant is changes by X?

Answer 18

The rate will change by X^2

Question 19

With second order reactants, what pattern does its half-life follow?

Answer 19

Increases with time

Question 20

Define overall order

Answer 20

The sum of the orders of all the different reactants

Question 21

If the overall order of a reaction is 0, what units does the rate constant have?

Answer 21

mol dm^-3 s^-1

Question 22

If the overall order of a reaction is 1, what units does the rate constant have?

Answer 22

s^-1

Question 23

If the overall order of a reaction is 3, what units does the rate constant have?

Answer 23

dm^3 mol ^-1 s^-1

Question 24

If the overall order of a reaction is 4, what units does the rate constant have?

Answer 24

dm^6 mol ^ -2 s^-1

Question 25

What is meant by the rate constant?

Answer 25

The constant that links the rate of reaction with the concentration of the reactants raised to the powers of their orders in a rate equation

Question 26

What form do rate equations take?

Answer 26

r = k[A]^m x [B]^n

Where A is the concentration of reactant A
Where B is the concentration of reactant B
Where m is the order of reactant A
Where n is the order of reactant B

Question 27

Define the term half-life

Answer 27

The time taken for HALF of the reactant to be used up

Question 28

What is the half-life pattern for zero order reactants?

Answer 28

Decreases with time

Question 29

What is the half-life pattern for first order reactants?

Answer 29

Remains constant throughout the reaction

Question 30

What is the half-life pattern for second order reactants?

Answer 30

Increases with time

Question 31

Define the term, the rate determining step

Answer 31

The slowest step in the reaction mechanism of a multi-step reaction

Question 32

Are chemicals in the rate equation in the rate determining step?

Answer 32

Yes

Question 33

In the rate equation, if a chemical is second order, how many moles of it will be in the rate determining step?

Answer 33

2 moles

Question 34

If identical chemicals appear on the same side of the reaction mechanism steps, what do we do?

Answer 34

ADD them together

Question 35

If identical chemicals appear on opposite side of the reaction mechanism steps, what do we do?

Answer 35

Subtract them

Question 36

Give the overall equation for this reaction

Step 1) 2N2O5 → N2O4 + 2NO3
Step 2) N2O4 + NO3 → NO + O2 + 2NO2
Step 3) NO + NO3 → 2NO2

Answer 36

2N2O5 → 4NO2 + O2

Question 37

What equation to find k, can only be used when the overall order is 1?

Answer 37

k = ln(2) / Half-life (seconds)

Question 38

What are the units for half-life?

Answer 38

Seconds (unless stated otherwise)

Question 39

Why does the equation k = ln(2) / Half-life only work when the overall order is 1?

Answer 39

First order reactants have a constant half-;life

Question 40

How can we investigate reaction rates using the initial rates method?

Answer 40

Step 1) Carry out the reaction, continuously measuring one reactant
Step 2) Use this to draw a concentration-time graph
Step 3) REPEAT the experiment using a different initial concentration
Step 4) REPEAT the process for each reactant at regular time intervals and find the rates and orders