Choosing reaction conditions - Higher
The conditions used for industrial reactions are carefully chosen.
Raw materials and energy
The conditions used are related to the availability and cost of:
- Basic material that goods are made from such as crops, metals, wood and animal products such as wool and leather.
- The capacity of a system to do work or the quantity required for mechanical work to take place. Measured in joules (J). For example, a man transfers 100 J of energy when moving a wheelbarrow. supplies
For example, hydrogen can be manufactured by reacting natural gas with steam, or by the The decomposition (breakdown) of a compound using an electric current. of water. The table shows some of the factors involved in choosing between these two methods.
| Gas and steam | Electrolysis of water | |
| Raw materials | Natural gas is a non-renewable resource | Water is readily available from rivers, lakes and oceans |
| Energy supplies | Strong heating using natural gas, coal or fuels from crude oil | Electricity can be generated using renewable resources |
| Raw materials | |
|---|---|
| Gas and steam | Natural gas is a non-renewable resource |
| Electrolysis of water | Water is readily available from rivers, lakes and oceans |
| Energy supplies | |
|---|---|
| Gas and steam | Strong heating using natural gas, coal or fuels from crude oil |
| Electrolysis of water | Electricity can be generated using renewable resources |
Question
A chemical company is planning to open a new factory to manufacture hydrogen. It has found a suitable site for the factory on the coast with nearby off-shore wind turbines. State which method, reacting natural gas with steam or electrolysis of water, is likely to be more suitable. Explain your answer.
Electrolysis of water is likely to be more suitable. Water is readily available from the sea, and the electricity needed can be generated by the wind turbines - provided that there is enough wind.
Control of reaction conditions
The reaction conditions used are chosen to obtain an acceptable The mass of product made in a chemical reaction. The percentage yield is a measure of the yield obtained compared to the maximum possible yield. of A substance formed in a chemical reaction. in an acceptable time. For example, there would be little The difference between revenue and costs. A key aim for all businesses. in getting a very high yield if it took several weeks or months to achieve. The The industrial chemical process that makes ammonia by reacting nitrogen and hydrogen together. for making ammonia provides a useful example of how this works:
N2(g) + 3H2(g) 鈬 2NH3(g) (forward reaction is Reaction in which energy is given out to the surroundings. The surroundings then have more energy than they started with so the temperature increases.)
Controlling temperature
If the temperature is increased, the A measure of the relative concentrations of substances in an equilibrium, showing if there are more reactants or products at equilibrium. moves in the direction of the Reaction in which energy is taken in. reaction. This means it moves to the left in the Haber process.
You might think that a low temperature is chosen, moving the equilibrium position to the right and making more ammonia. However, the rate of reaction is slow at low temperatures. So a compromise temperature of 450掳C is chosen. This is:
- low enough to achieve an acceptable yield
- high enough to do this in an acceptable time
Controlling pressure
If the Force exerted over an area. The greater the pressure, the greater the force exerted over the same area. is increased, the equilibrium position moves in the direction of the fewest A collection of two or more atoms held together by chemical bonds. of gas. This means it moves to the right in the Haber process.
You might think that a very high pressure is chosen to move the equilibrium position to the right, making more ammonia. However, it is expensive to achieve very high pressures. Stronger equipment is needed, and more energy is needed to compress the gases. So a compromise pressure of 200 A unit of pressure. is chosen. This is:
- low enough to keep costs down
- high enough to achieve an acceptable yield
Using a catalyst
A substance that changes the rate of a chemical reaction without being changed by the reaction itself. do not change the In chemical reactions, a situation where the forward and backward reactions happen at the same rate, and the concentrations of the substances stay the same. concentrations of reacting substances in reversible reactions. Instead, they increase the rate of reaction - often allowing a lower temperature to be used. Iron is a cheap catalyst used in the Haber process. It helps to achieve an acceptable yield in an acceptable time. It also allows a lower temperature to be used, which saves energy but also increases the yield of the reaction.
Question
State three reaction conditions that are controlled in industrial reactions.
Temperature, pressure, and the use of a catalyst.