CI - Rates, equilibria and the chemical industry Flashcards

1
Q

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

A

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

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2
Q

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

A

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

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3
Q

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

A

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.

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4
Q

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

A

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.

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5
Q

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

A

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

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6
Q

What are by-products?

A

Unwanted waste products from a chemical process.

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7
Q

What are co-products?

A

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

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8
Q

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

A

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.

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9
Q

What is there to consider when designing an industrial process?

A

The rate of reaction, product yield and cost.

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10
Q

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

A

The rate of reaction, product yield and cost.

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11
Q

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

A

Several different factors.

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12
Q

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

A

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

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13
Q

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?

A

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

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14
Q

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

A

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

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15
Q

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

A

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

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16
Q

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

A

High pressures make gaseous reactions go faster.

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17
Q

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

A

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.

18
Q

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

A

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.

19
Q

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

A

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.

20
Q

What is Kc?

A

The equilibrium constant.

21
Q

What is the symbol for the equilibrium constant?

A

Kc

22
Q

When is a system said to be in dynamic equilibrium?

A

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

23
Q

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

A

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

24
Q

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

A

The equilibrium constant, Kc.

25
Q

What does the equilibrium constant, Kc, show?

A

The ratio of products and reactants at dynamic equilibrium.

26
Q

What changes alter Kc?

A

Temperature changes.

27
Q

Do temperature changes alter Kc?

A

Yes.

28
Q

Do pressure changes alter Kc?

A

No.

29
Q

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

A

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.

30
Q

When will Kc increase because of a change in temperature?

A

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

31
Q

When will Kc decrease because of a change in temperature?

A

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

32
Q

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

A

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.

33
Q

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

A

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

34
Q

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

A

Nothing happens.

35
Q

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

A

NO EFFECT.

36
Q

What effect to catalysts have on the equilibrium of reactions?

A

They mean equilibrium is reached faster.

37
Q

Can catalysts increase the yield of a reaction?

A

No.

38
Q

What does the position of the equilibrium affect?

A

How economical a reaction is.

39
Q

How economical a reaction is depends on what?

A

The position of the equilibrium.

40
Q

When will an equilibrium not be economically viable?

A

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

41
Q

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

A

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.

42
Q

What are the risks involved in producing a chemical?

A

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.