The Chemical Industry

Question 1

What is the rate of a reaction?

Answer 1

A measure of how quickly reactants are converted into products. The rate of a reaction depends on the concentration of reactants and the rate constant.

Question 2

What is the rate equation of reaction:
nA + mB → C + D

Answer 2

Rate = k[A]^n[B]^m
Overall Order = n + m

Question 3

What is the rate constant?

Answer 3

A constant value that relates the rate of the reaction at a given temperature and the concentration of the reactants.

Question 4

What is order of a reaction?

Answer 4

A number of thats describes the relationship of a reactions concentration and the rate of a reaction.

Question 5

What is zero order?

Answer 5

Zero order is when the concentration of a reactant doesn’t have an effect on the rate. No included in the rate equation. Rate/Concentration graph will be a straight line.

Question 6

What is first order?

Answer 6

First order is when the concentration of a reactant has is directly proportional to the rate of reaction. [A] ∝ Rate
Rate = k[A]
Rate/Concentration graph is linear.

Question 7

What is second order?

Answer 7

Second order is when the concentration of the reactant squared is proportional to the rate.
[A]² ∝ Rate
Rate/Concentration graph produces increasing exponential curve.

Question 8

What does the gradient of a concentration/time graph represent?

Answer 8

The gradient represents the rate of reaction, a tangent can be draw at t=0 to work out the initial rate.

Question 9

How can you form a rate equation from a rate table?

Answer 9

Zero Order: change in concentration has no effect in the rate. Doesn’t appear in rate equation.
First Order: Rate ∝ Concentration. [A] in rate equation.
Second Order: Rate ∝ Concentration². [A]² in rate equation.

Question 10

What is Half-Life?

Answer 10

Half life is the time taken for the initial concentration of the reactions to decrease by half.
The half-life can be found from a concentration-time graph, looking at time for the concentration to half.
First Order half life constant so k = ln(2) / Half life

Question 11

How can you calculate rate?

Answer 11

Rate can only be determined through experimental data.
We can get this data by measuring a reactant’s or product’s change in mass/concentration throughout the reaction process.
Then plotting a concentration/volume/mass against time graph, using the gradient at t=0 to work out the initial rate.

Question 12

What is the Rate Determining Step?

Answer 12

The slowest step in a multi-step reaction. The overall rate is decided by this step. Species present in the rate determining step make up the rate equation.

Question 13

What is the Arrhenius Equation?

Answer 13

k = Ae^(-Ea/RT)
Where k = rate constant, A is the Frequency Factor, e is Euler’s Constant, Ea is the Activation Energy, R is the Gas Constant, T is the temperature (Kelvin).

Question 14

How can the Arrhenius Equation be expressed graphically?

Answer 14

lnk = -Ea/RT + lnA
Therefore on a graph of lnk against 1/T, the gradient is -Ea/R and the Y intercept is lnA.

Question 15

How does increasing the concentration or pressure effect Kc?

Answer 15

Kc is unaffected by the change of concentration/pressure, this is because they have no effect on the equilibrium position only allow equilibrium to be reestablished quicker.

Question 16

How does changing the temperature effect the position of the equilibrium?

Answer 16

If the forward reaction is exothermic:
Increase in temperature will favor the backwards reaction, decreasing the concentration of the products and increasing the concentration of the reactants, therefore altering the ratio of kc.

If the forward reaction is endothermic:
Increase in temperature will favor the forward reaction, increasing the concentration of the products and decreasing the concentration of the reactants, therefore altering the ratio of kc.

Question 17

Why do companies have to compromise between Rate of Reaction and Product Yield?

Answer 17

Changing reaction conditions can shift the position of equilibrium to favor the production of either products or reactants, but can also reduce the rate of reaction. So a greater proportion of desired product is being produced but at a lower rate.
An example of this is an exothermic reaction, lowering the temperature will favor the exothermic reaction but lower the rate of reaction.

Question 18

Why is nitrogen very unreactive?

Answer 18

Nitrogen has a triple covalent bond between two nitrogen atoms. Since this bond will need to break for a reaction to occur, a large activation energy is need cause a reaction.
Nitrogen molecules are also non-polar and not easily polarised. This makes it not prone to attack from electrophiles and nucleophiles.

Question 19

Describe the structure of Ammonia.

Answer 19

Ammonia has three hydrogen atoms which are covalently bonded to a nitrogen atom, leaving one lone pair of electrons.
Pyramidal shape with 107 degrees bond angle.
Ammonia is a nucleophile due to its lone pair of electrons.

Question 20

Describe the structure of the Ammonium Ion?

Answer 20

Ammonium ions have three hydrogens covalently bonded to the nitrogen and one dative covalent bond to a forth hydrogen, donated from lone pair.
Tetrahedral shape with 109.5 degrees bond angle.

Question 21

How can oxides of nitrogen be formed in combustion engines?

Answer 21

Due to the high temperature and pressure in an engine the nitrogen naturally in the air reacts with oxygen forming nitrous oxides.

Question 22

Describe the appearance of Nitrous Oxide, Nitric Oxide, and Nitrogen Dioxide.

Answer 22

Nitrous Oxide, N2O, a sweet-smelling colourless gas.
Nitric Oxide, NO, a colourless gas.
Nitrogen Dioxide, NO2, a brown gas.

Question 23

What reactions allow Nitrate (V) ions, Nitrate (III) ions, and Ammonium ions to be interconvertible?

Answer 23

2NH4 + 3O2 -> 2NO2 + 4H
2NO2 + O2 -> 2NO3
NO2 + 8H -> NH4 + 2H2O

Question 24

How can Nitrite ions be reduced to Nitric acid?

Answer 24

NO2 + e + 2H -> NO + H2O

Question 25

How can Nitric oxide be reduced to Nitrous Oxide?

Answer 25

2NO + 2e + 2H -> N2O + H2O

Question 26

How can you test for Nitrate (V) ions?

Answer 26

Warm the sample with Devarda’s alloy and NaOH, test the gas released with damp red litmus. If the paper turns blue this confirms the presence of nitrate (V) ions. This is due to the production of ammonia, which is basic.

Question 27

How can you test for ammonium ions?

Answer 27

Warm a sample with NaOH, test the gas released with damp red litmus paper. Paper will turn blue if the ammonium ions. This is due to the production of ammonia, which is basic.

Question 28

How is sustainability considered during a chemical reaction?

Answer 28

Need to consider costs, sources of raw material, energy to make conditions, and health and safety.