chemistry in society

Question 1

how are industrial processes designed?

Answer 1

to maximise profits and minimise the impact on the environment

Question 2

factors influencing industrial design

Answer 2

• availability, sustainability and cost of feedstock
• opportunities for recycling
• energy requirements
• marketability of by products
• product yield

Question 3

environmental factors taken into consideration when designing industrial processes

Answer 3

• minimising waste
  avoiding the use or production of toxic substances
• designing products which will be biodegradable if appropriate

Question 4

molar volume equation

Answer 4

mV = volume/number of moles

Question 5

percentage yield

Answer 5

used to compare the yield of a product actually obtained with what could have been obtained in theory
% yield = (actual yield/theoretical yield) x 100

Question 6

atom economy

Answer 6

measure of the % of reactant that becomes useful products, tells chemists how efficient a process is
% AE = mass desired products/total mass of reactants

Question 7

limiting and excess reactants

Answer 7

limiting = reactant in a chemical reaction which is used up when reaction stops
excess = reactants left over at the end of the reaction

Question 8

why do reaction rates need to be controlled?

Answer 8

if they are too low, the process will not be economical.
if they are too high, there is a risk of explosion.

Question 9

relative rate equation

Answer 9

relative rate = 1/time

Question 10

factors affecting reaction rate

Answer 10

concentration, particle size, temperature, pressure (gaseous reactants only), collision geometry

Question 11

reaction enthalpies

Answer 11

endothermic = positive enthalpy
exothermic = negative enthalpy

Question 12

activation energy

Answer 12

minimum energy required by particles to form an activated complex, if they don’t have sufficient energy then the collision will not occur.
difference between highest energy and energy of reactants on graph

Question 13

activated complex

Answer 13

unstable arrangement of atoms formed at the top of the potential energy barrier (found at top of graph)

Question 14

how does a catalyst affect the activation energy?

Answer 14

provides an alternative pathway for the reaction which has a lower activation energy, so more particles will have enough energy to collide

Question 15

how does changing temperature affect the reaction rates - energy distribution diagrams

Answer 15

increasing the temperature means more particles will have sufficient energy to collide, so the curve will be lower and longer on graph.

Question 16

enthalpy definition

Answer 16

measure of chemical energy in a substance

Question 17

enthalpy of combustion definition

Answer 17

energy change when one mole of a substance burns completely in oxygen

Question 18

what does Hess’s Law state?

Answer 18

enthalpy change of a reaction is independent of the route taken (no matter the route taken, the enthalpy change will always be the same for a reaction)

Question 19

molar bond enthalpy

Answer 19

energy required to break one mole of bonds in a diatomic molecule

Question 20

mean molar bond enthalpy

Answer 20

energy required to break one mole of bonds that occur in a non-diatomic molecule.
the mean is used for certain bonds as the energy required differs depending on where the bond is found.

Question 21

how do you calculate the enthalpy change for a reaction using bond enthalpies

Answer 21

energy put in - energy given out

Question 22

dynamic equilibrium

Answer 22

rates of forward and reverse reactions are equal.

Question 23

closed system

Answer 23

reaction is carried out in a sealed container so no reactants or products are lost

Question 24

describe the concentrations of reactants and products at equilibrium

Answer 24

constant but rarely equal

Question 25

why do chemists move the position of equilibrium?

Answer 25

to favour the products and maximise the profit

Question 26

how does temperature change affect the position of equilibrium?

Answer 26

increase favours endothermic reaction (shift in endo direction). decrease favours exothermic reaction (shift in exo direction)

Question 27

how does changing pressure affect the position of equilibrium?

Answer 27

increasing favours side with lower gas volume. decreasing favours side with higher gas volume. only affects gaseous substances.

Question 28

how does adding/removing reactants affect the position of equilibrium?

Answer 28

adding a reactant or removing a product will shift equilibrium to the right. adding a product or removing a reactant will shift equilibrium to the left.

Question 29

effect of catalysts on equilibrium

Answer 29

no effect on position but allows equilibrium to be reached faster and at a lower temperature.

Question 30

why is chromatography used?

Answer 30

to separate substances in complex mixtures, it works as substances travel at different speeds

Question 31

how can different substances be identified using chromatography?

Answer 31

by the distance they've travelled or the time taken to travel through the apparatus (retention time)

Question 32

if peaks on a chromatography graph can't be seen, what can be done?

Answer 32

dilution, or compare the components in two different graphs.

Question 33

volumetric analysis

Answer 33

uses a solution of accurately known concentration in a reaction to determine the concentration of another.

Question 34

use of titrations

Answer 34

used to accurately determine the volumes of solution required to reach the end point of a chemical reaction. knowing this volume can then lead to calculating concentrations.

Question 35

standard solution

Answer 35

a solution of accurately known concentration.

Question 36

use of redox titrations

Answer 36

based on redox reactions and used to determine the unknown concentration of a solution.

Question 37

why are indicators not always needed to determine end-points of reactions?

Answer 37

the solution may self-indicate. for example, acidified permanganate is purple but turns colourless when reduced.