CI - Rates, equilibria and the chemical industry

Question 1

In what 4 ways are there costs involved in producing a chemical?

Answer 1

1) Raw materials.
2) Fuel/energy.
3) Overheads/fixed costs.
4) Disposal costs.

Question 2

How can raw materials be a cost involved in producing a chemical?

Answer 2

The plant needs to buy chemical for the reaction - cheap, widely available ones are best.

Question 3

How can fuel/energy be a cost involved in producing a chemical?

Answer 3

Reactions needing high temperature or pressure will use up a lot of energy. Energy is also used in transporting chemicals to, from and around a plant, mixing them and purifying products.

Question 4

How can overheads/fixed costs be a cost involved in producing a chemical?

Answer 4

No matter how much fuel or raw material a company uses, there are certain costs that need to be met regularly. These include staff wages, rent of equipment or space, taxes, insurance, telephone bills, etc.

Question 5

How can disposal costs be a cost involved in producing a chemical?

Answer 5

Any unwanted by-products will have to be disposed of safely - this is subject to government regulations and can be very expensive.

Question 6

What are by-products?

Answer 6

Unwanted waste products from a chemical process.

Question 7

What are co-products?

Answer 7

Products which, whilst not as valuable as the main product, can still be useful and sold of for profit.

Question 8

What type of reactions tend to be best for keeping costs low?

Answer 8

Reactions with high atom economies and high percentage yields as they use fewer raw materials and have fewer waste products. This saves money for a company.

Question 9

What is there to consider when designing an industrial process?

Answer 9

The rate of reaction, product yield and cost.

Question 10

What needs to be balanced against each other to come up with the right reaction conditions?

Answer 10

The rate of reaction, product yield and cost.

Question 11

What do reaction conditions usually end up as a compromise between?

Answer 11

Several different factors.

Question 12

What are chemical engineers trying to do when designing an industrial process?

Answer 12

Make as much product as they can, as cheaply and as quickly as possible.

Question 13

Why when chemical engineers are designing an industrial process are they trying to make as much product as they can, as cheaply and as quickly as possible?

Answer 13

As this will make the company a bigger profit when they sell their product.

Question 14

What are the advantages of using high temperatures for an industrial process?

Answer 14

Reactions go faster at higher temperatures, meaning more product will be made in the same amount of time.

Question 15

What are the disadvantages of using high temperatures for an industrial process?

Answer 15

High temperatures make reactions more expensive to carry out because of the cost of fuel.

Question 16

What are the advantages of using high pressures for an industrial process?

Answer 16

High pressures make gaseous reactions go faster.

Question 17

What are the disadvantages of using high pressures for an industrial process?

Answer 17

To create a high pressure, gas must be pumped into the reaction vessel. Running powerful pumps uses a lot of energy and is expensive.

High pressures can be very dangerous. This means that reaction vessels must be made out of a strong material like thick steel, and incorporate safety systems. Again, this is very expensive.

Question 18

What are the advantages of using a catalyst for an industrial process?

Answer 18

The right catalyst can make a reaction go quickly at relatively low temperatures - in some cases, no heat is needed at all. This saves money on fuel.

Catalysts are a good investment because they don’t get used up.

Question 19

What are the disadvantages of using a catalyst for an industrial process?

Answer 19

Industrial catalysts can be expensive.

If a catalyst is in the same state as the reactants, it will have to be separated from the reaction mixture once the reaction is complete. This adds an extra step to the industrial process.

Question 20

What is Kc?

Answer 20

The equilibrium constant.

Question 21

What is the symbol for the equilibrium constant?

Answer 21

Kc

Question 22

When is a system said to be in dynamic equilibrium?

Answer 22

If the rate of the forward reaction is the same as the rate of the reverse reaction.

Question 23

What happens to the concentrations of the reactants and products at dynamic equilibrium?

Answer 23

The forwards and backwards reactions cancel each other out and there’s no overall change in the concentrations of the reactants and products.

Question 24

What is the ratio of products and reactants at dynamic equilibrium shown by?

Answer 24

The equilibrium constant, Kc.

Question 25

What does the equilibrium constant, Kc, show?

Answer 25

The ratio of products and reactants at dynamic equilibrium.

Question 26

What changes alter Kc?

Answer 26

Temperature changes.

Question 27

Do temperature changes alter Kc?

Answer 27

Yes.

Question 28

Do pressure changes alter Kc?

Answer 28

No.

Question 29

What happens to Kc if you change the temperature of a reaction?

Answer 29

The equilibrium shifts in the endothermic direction to absorb the extra heat. Meanwhile, of you decrease the temperature, the equilibrium shifts in the exothermic direction to try to replace the heat. If the change means more product is formed, Kc will rise. If it means less product is formed, then Kc will decrease.

Question 30

When will Kc increase because of a change in temperature?

Answer 30

If the change means more product is formed, Kc will rise.

Question 31

When will Kc decrease because of a change in temperature?

Answer 31

If it means less product is formed, then Kc will decrease.

Question 32

Why does Kc remain constant when you alter the pressure of a reaction?

Answer 32

Increasing the pressure shifts the equilibrium to the side with fewer gas molecules - this reduces the pressure. Decreasing the pressure shifts the equilibrium to the side with more gas molecules. This raises the pressure again. Kc stays the same, no matter what you do to the pressure.

Question 33

What happens to Kc if you change the pressure of a reaction?

Answer 33

Kc stays the same, no matter what you do to the pressure.

Question 34

What happens to Kc if you add a catalyst to a reaction?

Answer 34

Nothing happens.

Question 35

What effect do catalysts have on the position of the equilibrium?

Answer 35

NO EFFECT.

Question 36

What effect to catalysts have on the equilibrium of reactions?

Answer 36

They mean equilibrium is reached faster.

Question 37

Can catalysts increase the yield of a reaction?

Answer 37

No.

Question 38

What does the position of the equilibrium affect?

Answer 38

How economical a reaction is.

Question 39

How economical a reaction is depends on what?

Answer 39

The position of the equilibrium.

Question 40

When will an equilibrium not be economically viable?

Answer 40

If it gives a very low yield under the chosen conditions.

Question 41

Explain how in the haber process there is a compromise to find the best conditions?

Answer 41

1) Reaction is usually carried out at 400^oC and 200 atm of pressure. 2) High pressure favours the forward reaction, increasing the yield of ammonia. This is because the equilibrium moves to the side with fewer molecules - the product side. High pressure also speeds up the reaction. 3) A pressure of 200 atm is a compromise. A greater yield and faster rate could be achieved at higher pressures, but maintaining a high pressure is expensive and has the potential to be dangerous. 4) High temperature makes the reaction go faster too - it increases the kinetic energy of the reactant molecules. But, it also lowers the product yield because the forward reaction is exothermic - high temperatures shift the position of the equilibrium to the left, to absorb the extra heat. 5) A reaction temperature of 400^oC is a compromise. A greater yield could be achieved at lowers temperatures, but the reaction would be too slow to be economical - there's no point waiting years to get your product, even if you eventually make loads. At higher temperatures the reaction would go faster, but the yield would become too low to produce ammonia efficiently.

Question 42

What are the risks involved in producing a chemical?

Answer 42

1) Some chemicals, especially gases, are highly flammable and carry the risk of explosion, e.g. propane, pressurised hydrogen. They must be stored and handled correctly to minimise this risk. 2) Some chemicals are harmful to our health if we come into contact with them or their vapours. Chlorine, for example, is toxic if inhaled and can irritate the eyes and lungs. Worker sin the chemical industry are most at risk, but an accidence or fire at a chemical plant, or a spill during transportation, could also expose the public to hazardous material. 3) Some chemicals can also damage the environment. Sulfur dioxide is a by-product of sulfuric acid production. It is an acidic gas and a contributor to acid rain.