Unit 3 - Chemistry in Society

Question 1

Industrial processes

Answer 1

Industrial processes are designed to maximise profit and minimise effect to the environment

Factors influencing process design include:

• availability
• sustainability
• cost of feedstocks
• opportunities for recycling
• energy requirements
• marketability of byproducts
• product yield

Environmental considerations include:

• minimising waste
• avoiding use/ production of toxic substances
• ability to make products biodegradable

Question 2

Raw materials/ feedstocks

Answer 2

Raw materials include fossil fuels, mineral ores, minerals, air and water.

Feedstocks are extracted or synthesised from raw materials. They are the chemicals that have to be reacted or processed in order to make a product.

Question 3

Molar volume

Answer 3

Molar volume (Vm) is the volume occupied by 1 mole of gas when measured at a given temperature and pressure

The molar volume for any gas is the same as long as its measured at the same pressure and temperature

Vm unit: lmol^-1

Molar volume = volume/ number of moles

Vm = v/n

Question 4

Chemical reaction efficiency

Answer 4

Percentage yield: the efficiency in which reactants are converted into the desired product

Atom economy: the proportion of the total mass of all reactants successfully converted into the desired product, the nearer the value to 100 percent the less waste there is

Question 5

Equilibrium

Answer 5

Equilibrium:

• the rate of the forward and reverse reaction are equal to one another
• the reactants are converted into products at the same rate products are converted back into reactants
• the concentration of reactants and products remain constant, yet rarely equal
• double headed arrow represents equilibrium (the bigger arrow shows the favoured reaction)

Altering pressure, temperature or concentration causes the position of equilibrium to (temporarily) shift to reduce the effects of the imposed conditions.

Effect of temperature:

• Increasing temperature causes equilibrium to shift in the direction of the endothermic reaction (iNcrease=eNdothermic)
• Decreasing temperature causes equilibrium to shift in the direction of the exothermic reaction

Effect of pressure:

• [volume of gas is directional proportional to the number of moles of gas present]
• Increasing pressure causes equilibrium to shift to the side with the smaller gaseous volume
• Decreasing pressure causes equilibrium to shift to the side with the larger gaseous volume

Effect of concentration:

• Increasing concentration of a substance causes equilibrium to favour the reaction that will cause more of the substance(s) on the other side of the equation to be formed
• Decreasing concentration of a substance causes equilibrium to favour the reaction that will cause more of that substance to be formed

Effect of catalyst:

• increases the rate of both the forward and reverse reaction equal, so increases the rate at which equilibrium is formed
• does not affect the position of equilibrium

Question 6

Chemical energy

Answer 6

Chemical energy is also known as enthalpy

Enthalpy change of a reaction can be calculated by: total bond enthalpy before - total bond enthalpy after

Types of enthalpy change reactions:

• Enthalpy of formation (ΔHf)… of a compound is the enthalpy change when one mole of a compound is formed from its elements
• Enthalpy of combustion (ΔHc)… is the enthalpy can that occurs when one mole of a substance is burned completely in oxygen (always -ve)
• Enthalpy of solution (ΔHs)… is the energy change when one mole of the substance dissolves in water (can be +ve or -ve)
• Enthalpy of neutralisation (ΔHn)… of an acid is the energy change when it is neutralised (by adding an alkali) to form one mole of water

Heat energy transferred:
Eh = cmΔT

Question 7

Hess’s law

Answer 7

Hess’s law states that the enthalpy change for a chemical reaction is independent of the route taken

Question 8

Types of chemical analysis test

Answer 8

Qualitative: tests for the presence of a substance

Quantitative: tests for the amount of a substance

Question 9

Chemical analysis techniques

Answer 9

Flame testing:

• qualitative
• introducing a sample into a flame then observing its colour

Precipitation:

• qualitative
• two solutions are mixed and a precipitate is formed

Gravimetry:

• quantitative
• after precipitation reaction, filter off precipitate and weigh, calculations (e.g. to find concentration of ions in solution)

Volumetric analysis - titrations:

• quantitative
• using a solution of a known concentration to determine the amount of another substance present

Thin layer chromatography - paper chromatography:

• qualitative
• sample applied to base line then dipped in shallow solvent, solvent moves up paper and mixture separates
• Rf value (used to determine what substances are present) = distance from base line to solvent front (highest point liquid has travelled to)/ distance from base line to spot sample travelled to

Column chromatography:

• qualitative
• used to separate individual chemical compounds from mixtures
• sample substance travels through column, each substance takes a different amount time to travel through -retention time-that can be used to identify it

Gas chromatography:

• qualitative/ quantitative
• the rate of travel of a substance through the column is the retention time and can be graphed, the peaks can then be used to identify the substance (height of peak correlates to quantity of substance)