Chemistry in Society

Question 1

Industrial Processes

Answer 1

Industrial processes are designed to maximise profit and minimise the impact on the environment.

Question 2

Factors influencing industrial process design include

Answer 2

-availability, sustainability and cost of feedstock(s)
-opportunities for recycling
-energy requirements
-marketability of by-products
-product yield

Question 3

Environmental considerations include

Answer 3

-minimising waste
-avoiding the use or production of toxic substances
-designing products which will biodegrade if appropriate

Question 4

information for calculations

Answer 4

-Chemical equations, using formulae and state symbols, can be written and balanced to show the mole ratio(s) of reactants and products.
-The mass of a mole of any substance, in grams (g), is equal to the gram formula mass and can be calculated using relative atomic masses.
-Calculations can be performed using the relationship between the mass and the number of moles of a substance.
-For solutions, the mass of solute (grams or g), the number of moles of solute (moles or mol), the volume of solution (litres or l), or the concentration of the solution (moles per litre or mol l-1), can be calculated from data provided.
-The molar volume (litres mol-1) is the volume occupied by one mole of any gas at a certain temperature and pressure. The molar volume is the same for all gases at the same temperature and pressure.
-Calculations can be performed using the relationship between the volume of gas, molar volume and the number of moles of a substance.

Question 5

Extra Calculation Information

Answer 5

-The efficiency with which reactants are converted into the desired product is measured in terms of the percentage yield and atom economy.
-The ‘theoretical yield’ is the quantity of desired product obtained, assuming full conversion of the limiting reagent, as calculated from the balanced equation.
-The ‘actual yield’ is the quantity of the desired product formed under the prevailing reaction conditions.
-The atom economy measures the proportion of the total mass of all starting materials converted into the desired product in the balanced equation.
-Reactions which have a high percentage yield may have a low atom economy value if
large quantities of by-products are formed.

Question 6

Reaction Rates

Answer 6

Reaction rates must be controlled in industrial processes. If the rate is too low then the process will not be economically viable; if it is too high there will be a risk of explosion.

Question 7

Potential Energy Diagram

Answer 7

-A potential energy diagram can be used to show the energy pathway for a reaction.
-The enthalpy change is the energy difference between the products and the reactants.
-The enthalpy change has a negative value for exothermic reactions or a positive value for endothermic reactions.

Question 8

Activation energy(potential energy diagrams)

Answer 8

The activation energy is the minimum energy required by colliding particles to form an activated complex and can be calculated from potential energy diagrams

Question 9

Activated Complex

Answer 9

The activated complex is an unstable arrangement of atoms formed at the maximum of the potential energy barrier, during a reaction.

Question 10

Catalyst

Answer 10

-A catalyst provides an alternative reaction pathway with a lower activation energy.
-A potential energy diagram can be used to show the effect of a catalyst on activation energy.

Question 11

Temperature

Answer 11

-Temperature is a measure of the average kinetic energy of the particles in a substance.
-The effects of temperature and of adding a catalyst can be explained in terms of a change
in the number of particles with energy greater than the activation energy.

Question 12

Activation Energy

Answer 12

The activation energy is the minimum kinetic energy required by colliding particles before a reaction may occur.

Question 13

Enthalpy

Answer 13

-Enthalpy is a measure of the chemical energy in a substance.
-The enthalpy change associated with a reaction can be calculated from the quantity of heat energy released.

Question 14

Exothermic Reaction

Answer 14

A reaction or process that releases heat energy is described as exothermic. In industry, exothermic reactions may require heat to be removed to prevent the temperature rising.

Question 15

Endothermic Reaction

Answer 15

A reaction or process that takes in heat energy is described as endothermic. In industry, endothermic reactions may incur costs in supplying heat energy in order to maintain the reaction rate.

Question 16

molar bond enthalpy

Answer 16

The molar bond enthalpy is the energy required to break one mole of bonds in a diatomic molecule. A mean molar bond enthalpy is the average energy required to break one mole of bonds, for a bond that occurs in a number of compounds.

Question 17

Quantity of heat energy

Answer 17

-The enthalpy change associated with a reaction can be calculated from the quantity of heat energy released.
-The quantity of heat energy released can be determined experimentally and calculated using Eh=cmΔT.
The quantities Eh, c, m or ΔT can be calculated, in the correct units, given relevant data.
-The enthalpy of combustion of a substance is the enthalpy change when one mole of the substance burns completely in oxygen.
Hess’s law states that the enthalpy change for a chemical reaction is independent of the route taken. The enthalpy change for a reaction can be calculated using Hess’s law, given appropriate data.

Question 18

bond enthalpies

Answer 18

Bond enthalpies can be used to estimate the enthalpy change occurring for a gas phase reaction, by calculating the energy required to break bonds in the reactants and the energy released when new bonds are formed in the products.

Question 19

Equilibria

Answer 19

-In a closed system, reversible reactions attain a state of dynamic equilibrium when the rates of forward and reverse reactions are equal.
-At equilibrium, the concentrations of reactants and products remain constant, but are rarely equal.
-To maximise profits, chemists employ strategies to move the position of equilibrium in favour of the products.
-For a given reversible reaction, the effect of altering temperature or pressure or of adding/removing reactants/products can be predicted.
-The addition of a catalyst increases the rates of the forward and reverse reactions equally. The catalyst increases the rate at which equilibrium is achieved but does not affect the position of equilibrium.

Question 20

Chromatography

Answer 20

-Chromatography is a technique used to separate the components present within a mixture. Chromatography separates substances by making use of differences in their polarity or molecular size.
-The details of any specific chromatographic method or experiment are not required. Depending on the type of chromatography used, the identity of a component can be indicated either by the distance it has travelled, or by the time it has taken to travel through the apparatus (retention time).
-The results of a chromatography experiment can sometimes be presented graphically, showing an indication of the quantity of substance present on the y-axis and retention time
of the x-axis.

Question 21

Volumetric Analysis

Answer 21

Volumetric analysis involves using a solution of accurately known concentration in a quantitative reaction to determine the concentration of another substance.

Question 22

Titration

Answer 22

Titration is used to determine, accurately, the volumes of solution required to reach the end-point of a chemical reaction. An indicator is normally used to show when the end-point is reached. Titre volumes within 0·2 cm3 are considered concordant.

Question 23

Standard Solutions

Answer 23

Solutions of accurately known concentration are known as standard solutions.

Question 24

Redox Titrations

Answer 24

Redox titrations are based on redox reactions. In titrations using acidified permanganate, an indicator is not required, as purple permanganate solution turns colourless when reduced.

Question 25

Calculations with Titrations

Answer 25

-concentration of one reactant can be calculated given the concentration of the other reactant and the volumes of both solutions
-volume of one reactant can be calculated given the volume of the other reactant and the concentrations of both solutions

Question 26

Collision Theory

Answer 26

substances can only react with each other if:
-the particles collide with each other
-the collisions have enough energy
-at the correct orientation during collision

Question 27

Successful collision

Answer 27

-particles collide with the correct geometry+collide with the correct kinetic energy above or equal to the activation energy.
-The speed of the reaction is dependent on the ratio of successful to unsuccessful collisions per minute. The more successful collision the faster the reaction.
-Example= as the reaction proceed there are fewer reactants, therefore fewer collisions and hence less successful collision, reaction rate decreases towards the end of the reaction

Question 28

How was the concentration of the reactant varied and why

Answer 28

-by changing the volume of the reactant and adding water to keep overall volume constant
-to keep concentration of the other reactants the same/constant so there is only one variable changed

Question 29

Suggest why the procedure adopted to determine the rate of reaction was accurate

Answer 29

colour change is instant to determine end point and not gradua

Question 30

Change of concentration on a graph

Answer 30

Line going up to the right with no levelling off

Question 31

Concentration(energy distribution graphs)

Answer 31

-decreasing activation energy means increasing the area to the right of Ea along the kinetic energy axis.
-an increase in concentration increases the area under the distribution curve. Increasing concentration also increase the height of the graph at all positions, due to more particles present with each kinetic energy.
-more collision=more successful collision, hence the reaction rate increases with increased concentration.

Question 32

How does an increase in concentration affect the rate of reaction

Answer 32

An increase in concentration increases the number of particles equal or above to the activation energy, which means there will be more collisions resulting in more successful collisions with the correct orientation and energy

Question 33

Calculating the relative rate

Answer 33

1 divided by the time, units= s to the minus 1

Question 34

Pressure

Answer 34

increase in pressure increases the rate of reaction due to the decrease in volume thereby increasing the concentration of particles, more collisions occur leading to an increase in rate of reaction.

Question 35

Temperature

Answer 35

-measure of the average kinetic energy of the particles in a substance, which also means it’s the indicator of the speed of the particles
-the higher the temp the greater the kinetic energy of the particles which means there will be more collisions equal or above the activation energy increasing the number of successful collisions

Question 36

why is the beaker dry?

Answer 36

so there would not be any other chemicals present in the beaker, as it can interfere with the concentration

Question 37

why is reaction time less accurate when experiment is carried out at room temp?

Answer 37

hard to determine the end point due to gradual colour change

Question 38

SUMMARY IN GRAPH

Answer 38

-Concentration versus rate in a direct relationship and shows a linear relationship
-Temperature versus rate is a direct relationship but rises exponentially in a graph(since a 10 degree rise doubles the rate)

Question 39

Temperature affects relative rate

Answer 39

-the higher the temp the greater the kinetic energy(higher speed) of the particles results in greater energy during collisions which means there will be more collisions equal or above the activation energy increasing the number of successful collisions

Question 40

Energy Distribution graph TEMPERATURE

Answer 40

-higher temperature graphs are lower and further along=which means more particles who have equal or above energy of activation energy
-molecules above the activation energy have sufficient energy to react/to form an activated complex
-larger area=more successful collisions

Question 41

Particle size

Answer 41

Collisions between particles can only occur on the surface of solid(marble). With smaller particle sizes there is a greater surface area and hence more collisions, increasing number of collisions

Question 42

Description of method using balance

Answer 42

-weigh mass of marble chips
-place everything on balance and weigh
-pour marble into flask and use cotton wool
-start timer and place beaker back onto the balance
-measure everything on the balance every required interval

Question 43

Enthalpy change formulas

Answer 43

E1=products
E2=reactants
E3=point of maximum collision

enthalpy change forward reaction= E1-E2
enthalpy change reverse reaction= E2-E1
activation energy forward reaction= E3-E2
activation energy reverse reaction=E3-E1

Question 44

Catalyst Poisoning

Answer 44

occurs when the surface of the catalysts becomes contaminated with impurities. Reactant cannot adsorb and then catalyst stops working). If the contaminant is soot(carbon) then burning it off can regenerate the catalyst.

Question 45

Effect of catalyst on graphs

Answer 45

-the catalyst can be also be shown on potential diagrams, it lowers activation energy(hump) and does not affect enthalpy change
-since catalyst lowers activation energy, the area to the right of it increase which increase the number of particles with kinetic energy greater than or equal to activation energy, therefore more collisions can form the activated complex increases rate of reaction.

Question 46

why does the platinum wire not have to be continually heated

Answer 46

it was catalyzing the reaction, so it kept on glowing.