Chemical Industry

Question 1

What are different ways of measuring rate of a reaction? (5)

Answer 1

• volume of gas produced
• mass change
• pH
• colorimetry
• chemical analysis using titration

Question 2

What is rate?

Answer 2

How quickly a quantity of something changes

Question 3

What is reaction rate?

Answer 3

change in the amount of reactants or products per unit time

Question 4

How can you work out reaction rate?

Answer 4

By using a tangent on a concentration-time graph

Question 5

What’s the equation for initial rate?

Answer 5

Amount of reactant used or product formed / time

Question 6

How do you work out reaction rate from conc-time graph?

Answer 6

Work out the gradient using a tangent

Question 7

What is the initial rate of reaction?

Answer 7

The rate at the start of the reaction

Question 8

What do you assume in the initial rates method?

Answer 8

• Conc of other reactants isn’t changing significantly
• Temp stays constant
• Reaction has not proceeded too far

Question 9

What is the equation for initial rate?

Answer 9

initial rate = amount of reactant used or product formed / time

Question 10

What is a clock reaction?

Answer 10

A reaction which has a easily observable endpoint

Question 11

What is the rate equation?

Answer 11

Rate = k[A]^m[B]^n
m and n are orders of reaction
k is rate constant (units of k vary)

Question 12

What does zero order with respect to [A] mean?

Answer 12

[A] changes and the rate stays the same

Question 13

What does 1st order with respect to [A] mean?

Answer 13

rate is proportional to [A] (if [A] doubles rate doubles)

Question 14

What does 2nd order with respect to [A] mean?

Answer 14

Rate is proportional [A]^2 (if [A] doubles rate will be 2^2)

Question 15

What is the overall order of a reaction?

Answer 15

The sum of all the orders of the different reactants

Question 16

What does the order of reaction with respect to a particular substance tell you?

Answer 16

Tells you how a reactants concentration affects the rate

Question 17

How do you work out the orders?

Answer 17

Do initial rates method experiment to see how reactant affects the rate one by one

Question 18

What is the half life of a reaction?

Answer 18

The time taken for a reactant to half in quantity

Question 19

What does half life look like for zero order?

Answer 19

half life decreases as reaction goes on

Question 20

What does half life look for first order?

Answer 20

half life decreases as conc does but is constant

Question 21

What does half life look like for 2nd order?

Answer 21

Half life increases as reaction goes on

Question 22

how do you work out rate constant using half lifes?

Answer 22

k = ln2/t1/2

Question 23

What is t1/2?

Answer 23

half life

Question 24

When does the rate constant valid?

Answer 24

At a specific temperature for that equation

Question 25

What do the parts of the Arrhenius equation mean?

K = Ae^(-Ea/RT)

Answer 25

K= rate constant
Ea = activation enthalpy
T = temperature (K)
R = gas constant
A = pre-exponential factor

Question 26

What does a large Ea mean for the arrhenius equation?

k = Ae^(-Ea/RT)

Answer 26

means a slow rate of reaction because higher activation enthalpy means not as many particles will react

Question 27

What do you plot against each other in the arrhenius plot

Answer 27

lnk against 1/T

Question 28

What is the rate determining step (rate limiting step)

Answer 28

It is the slowest step in a multi-step reaction

Question 29

What does the order of a reaction tell you about the molecules in the rate determining step?

Answer 29

shows the number of molecules in the rate determining step

Question 30

What costs are involved in producing a chemical?

Answer 30

1) raw materials
2) Fuel/energy needed
3) fixed costs (eg. labour)
4) Disposal Costs

Question 31

What reactions save the most money?

Answer 31

Reactions with high atom economies and high percentage yields

Question 32

What should be considered when designing an industrial process, to find the right reaction conditions?

Answer 32

rate of reaction
product yield
cost

Question 33

What are advantages and disadvantages of high temp for an industrial process?

Answer 33

+
The reaction goes faster
-
more expensive because of fuel

Question 34

Advantages and disadvantages of high pressure for an industrial process?

Answer 34

\+
the reaction goes faster
-
expensive
strong material needs to be used because high pressure is dangerous

Question 35

Advantages and disadvantages of a catalyst for an industrial process?

Answer 35

\+
faster reaction at lower temps
good investment as don't get used up
-
can be expensive
homogeneous catalyst has to be separated from  products

Question 36

What is Kc?

Answer 36

the equilibrium constant

Question 37

What is dynamic equilibrium?

Answer 37

• rate of forward reaction is equal to rate of back reaction

- so there’s no overall change in conc of reactants and products

Question 38

What is the equation for Kc?

aA + bB dD + eE

Answer 38

Kc = ([D]^d x [E]^e) / ([A]^a x [B]^b)

Question 39

Do temperature changes alter Kc?

Answer 39

Yes - Kc is only valid at specific temperatures

Question 40

Do pressure changes alter Kc?

Answer 40

No

Question 41

Do catalysts alter Kc?

Answer 41

catalysts have no effect

Question 42

Do you have to work out the units for Kc?

Answer 42

yes - (work it out for mol/dm)