Rates, Equilibria and the Chemical Industry

Costs in producing a chemical

• Costs that need to be considered:

  • Raw materials

    • The plant needs to buy chemicals for the reaction. Cheap, widely available chemicals are the most economical

  • Fuel/energy

    • 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

  • Overheads/fixed costs

    • 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

  • Disposal costs

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

• Reactions with high atom economies and percentage yields are best as they produce the least waste saving money for the company

Choosing conditions for an industrial reaction

• Rate of reaction, product yield, and cost must all be balanced against each other to come up with the right reaction conditions

Equilibrium constant

• For a reversible reaction at dynamic equilibrium, the concentration of reactants and products are constant.

• The ratio of products and reactants at dynamic equilibrium is shown by the equilibrium constant, K_c

• For the general equation: aA + bB ⇋ dD + eE

• K_c = [D]^d[E]^e / [A]^a[B]^b

Factors affecting K_c

• Increasing temperature will shift the position of equilibrium in the endothermic direction. If this results in more product being formed, K_c will increase. If this results in less product being formed K_c will decrease

• Increasing pressure will shift the position of equilibrium in the direction producing the least moles. This has no affect on K_c

• Catalysts have no affect on the position of equilibrium and no affect on K_c

Risks involved in producing a chemical

• Some chemical, especially gases, are highly flammable and carry a risk of explosion. They must be stored and handled carefully and correctly

• Some chemicals are harmful and toxic

• Some chemicals can damage the environment such as sulfur dioxide (a by product of sulfuric acid production) causes acid rain.