Unit 3

Question 1

What factor influence process design?

Answer 1

Factors influencing process design include:

• availability, sustainability and cost of feedstock(s)
• opportunities for recycling
• energy requirements

Question 2

What do environmental considerations include

Answer 2

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

Question 3

What can be done to ensure costly reactants are converted into product

Answer 3

In order to ensure that costly reactant(s) are converted into product, an excess of less expensive reactant(s) can be used.

Question 4

What effect will using excess reactants have on the atom economy

Answer 4

Whilst the use of excess reactants may help to increase percentage yields, this will be at the expense of the atom economy so an economic/environmental balance must be struck.

Question 5

What happens at equilibrium

Answer 5

At equilibrium, the concentrations of reactants and products remain constant, but are rarely equal.

Question 6

What can be done to maximise profits?

Answer 6

To maximise profits, chemists employ strategies to move the position of equilibrium in favour of the products.

Question 7

Why is it essential that chemists predict the quantity of heat energy taken in or given out

Answer 7

• Endothermic reactions may incur costs in supplying heat energy in order to maintain the reaction rate.
• Exothermic reactions may require removal of heat to prevent the temperature rising

Question 8

What is enthalpy of combustion?

Answer 8

• Enthalpy of combustion of a substance is the enthalpy change when one mole of the substance burns completely in oxygen.

Question 9

What does hess’s law state?

Answer 9

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

Question 10

How can enthalpy of combustion values be obtained?

Answer 10

Enthalpy of combustion values can often be directly measured using a calorimeter and values for common compounds are available from data books and online databases for use in Hess’s law calculations.

Question 11

What are molar bond enthalpy?

Answer 11

Mean molar bond enthalpies are average values which are quoted for bonds which occur in different molecular environments.

Question 12

What is an oxidising agent & reducing agent

Answer 12

• An oxidising agent is a substance which accepts electrons.
• A reducing agent is a substance which donates electrons.

Question 13

What happens to elements with low electronegatitivies

Answer 13

• The elements with low electronegativities tend to form ions by losing electrons (oxidation) and so react as reducing agents.
• The elements with high electronegativities tend to form ions by gaining electrons (reduction) and so can act as oxidising agents.

Question 14

What are examples of strong oxidising agents?

Answer 14

• The dichromate and permanganate ions are strong oxidising agents in acidic solutions.
• Hydrogen peroxide is an example of a molecule which is an oxidising agent.

Question 15

What is an example of a gas that acts as a reducing agent?

Answer 15

Carbon monoxide is an example of a gas that can be used as a reducing agent.

Question 16

Why are oxidising agents widely employed?

Answer 16

• Oxidising agents are widely employed because of the effectiveness with which they can kill fungi and bacteria, and can inactivate viruses.
• The oxidation process is also an effective means of breaking down coloured compounds making oxidising agents ideal for use as ‘bleach’ for clothes and hair.

Question 17

What is retention time?

Answer 17

Depending on the type of chromatography in use, 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

Question 18

What does volumetric analysis involve

Answer 18

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

Question 19

What is an indicator?

Answer 19

An indicator is a substance which changes colour at the end-point.

Question 20

What is an endpoint

Answer 20

The end-point is the point at which the reaction is just complete.

Question 21

Why are substances such as potassium manganate very useful reactants in redox titrations?

Answer 21

Substances such as potassium manganate(VII), which can act as their own indicators, are very useful reactants in redox titrations.