Chemical Industries

Question 1

State the basic chemical rate equation

Answer 1

A + B –> C + D

Rate = k[A]^m[B]^n

Question 2

What unit is used for rate of reaction?

Answer 2

mol dm^-3 s^-1

Question 3

Explain zero order rates

Answer 3

Concentration of species has no impact on rate
Shown on rate concentration graph as a horizontal line
Rate = k

Question 4

Explain first order rates

Answer 4

Concentration of species is directly proportional to rate
Doubling concentration doubles rate
Rate = k[A]

Question 5

Explain second order rates

Answer 5

Rate is proportional to concentration of species squared.
Doubling concentration increases rate by four times
Rate = k[A]^2

Question 6

How does a zero order reaction look on a concentration-time graph?

Answer 6

Zero order reaction on concentration-time graph looks linear

Question 7

How do first and second order reactions look on a concentration-time graph?

Answer 7

Both are curved, second order graphs have a slight kink in the curve

Question 8

How do you calculate the rate in a concentration-time graph?

Answer 8

Draw tangent, find gradient of tangent

Question 9

What effect on initial rate would zero, first and second order reactions have on doubling the concentration of a species?

Answer 9

Zero order - no change in initial rate
First order - Initial rate doubles
Second order - Initial rate quadruples (2^2)

Question 10

Define half life

Answer 10

The time for the initial concentration of the reactants to decrease by half

Question 11

How does the half life change over the course of a first order reaction?

Answer 11

Half life is constant in a first order reaction

Question 12

Explain the progress curves and initial rate method for finding out the rate order of a reaction?

Answer 12

Measuring the change volume/concentration/pH of products/reactants to draw a progress curve graph. Gradient of a tangent can be calculated to find rate.
Then find order using initial rate method:
Draw tangent at t=0 for different progress curves, find order graphically (straight line is 1st in rate/conc. graph, straight line against rate/conc.^2 is 2nd, line is flat in 0)

Question 13

What is the rate determining step?

Answer 13

The slowest step of the reaction, which determines the overall rate. The rate equation includes all species in each stage up to and including rate determining step.

Question 14

If the forward reaction is endothermic, how will an increase in temperature change the position of the equilibrium?

Answer 14

The equilibrium will shift to the right to oppose the change, Kc will increase

Question 15

Why is nitrogen highly unreactive?

Answer 15

Triple bonds require lots of energy to break. Bonds are non polar and not easily polarizable, so electro/nucleophiles are not attracted to them, making them less likely to be involved in reactions.

Question 16

Name three common nitrogen oxides, how they appear and where they come from

Answer 16

NO: a colourless gas turns to NO2 in air. Formed from combustion processes especially from vehicle engines, thunderstorms, denitrifying bacteria in soil

NO2: a brown gas, formed from oxidation of NO in atmosphere

N2O: a sweet smelling colourless gas, formed in the soil by denitrifying bacteria

Question 17

How would you test for nitrate (V) ions?

Answer 17

Warm the sample with NaOH and Devarda’s Alloy, if present gas present should turn red litmus paper blue.

Question 18

Write out the reaction of aerobic bacteria in the soil oxidising ammonium ions

Answer 18

NH4+ + 1.5O2 –> NO2- + 2H+ + H2O

Nitrate (III) ion is further oxidised to nitrate (V) ion: NO2- + 1.5O2 –> NO3-

Question 19

Write out the reaction when anaerobic bacteria reduce nitrate (V) ions when oxygen is low

Answer 19

NO3- (aq) –> NO (g) –> N2O (g) –> N2 (g)

Question 20

How do catalysts affect the position of equilibrium/Kc?

Answer 20

Catalysts do not affect the position of the equilibrium, they only alter the rate at which the equilibrium is attained

Question 21

How do concentration and total pressure affect Kc and composition of mixture?

Answer 21

Changes in concentration and total pressure may alter the composition of equilibrium mixtures, but they do not alter the value of Kc, provided temperature does not change

Question 22

What is the unit of k in:
0 order reactions
1st order reactions
2nd order reactions

Answer 22

0 order: k = mol dm^-3 s^-1
1st order: k = s^-1
2nd order: k = dm^3 mol^-1 s^-1

Question 23

What are the units in Arrhenius’ Equation?

Answer 23

k = Ae^-Ea/RT
T = temperature in kelvin
R = gas constant (8.314 J K^-1 mol^-1)
Ea = activation energy in J mol^-1
A = frequency factor (constant)

Question 24

What is the gradient in a graph of ln(k) over 1/T?

Answer 24

Gradient = -Ea/R

Question 25

Explain the reciprocal reaction time method for finding rate order of a reaction

Answer 25

Measure how long the reaction takes to produce a small fixed amount of a product (reaction time)
Plot graph of 1/T against concentration of solution, showing rate

Question 26

What are feedstocks?

Answer 26

Reactants made from raw materials that go into a chemical process

Question 27

What is the difference between co-products and bi-products?

Answer 27

Co-products are desirable secondary products that are formed during the manufacturing process
Bi-products are unwanted secondary products

Question 28

What is the aim of green chemistry?

Answer 28

Minimise use of feedstocks
Recycle unused solvents and reactants
Minimise energy consumption