SC12 Flashcards
SC12a
1) Describe what happens in reversible reactions.
2) Explain the use of the symbol ⇌ in chemical equations.
3) Explain what is meant by dynamic equilibrium.
1) If two reactants are put together, they will start to react and products will form. The reactant concentration will fall and the products concentration will rise. As the product concentration starts to rise, the backwards reaction will start to happen. The more products there are, the faster the backwards reaction.
2) The symbol means that the reaction is reversible, and can go in both directions.
3) Dynamic equilibrium occurs because the reactions are no longer changing. This is called dynamic equilibrium because the reactions are still occurring (dynamic) but the substances remain in balance (equilibrium). At dynamic equilibrium, the rates of the forward and the backward reactions are equal and the relative concentrations of the reactants and products at equilibrium do not change.
SC12a
1) Describe the formation of ammonia.
2) State the conditions used for the Haber process, and what type of catalyst is used?
3) How should the concentration of reactants be altered to increase the rate of product formation if equilibrium lies to the left?
1) Ammonia is produced via the Haber process. This involves reacting nitrogen with hydrogen in a special chamber. The nitrogen comes from the air and the hydrogen is extracted from natural gas. This reaction is reversible, which means that some of the ammonia also breaks down to reform hydrogen and nitrogen.
2) The conditions used in the Haber Process are high pressure (around 200 atmospheres) and high temperature (around 450°C). These conditions are necessary to make the reaction happen quickly and produce enough ammonia to be useful. This process happens in the presence of an iron catalyst.
3) If the equilibrium lies to the left, it means that there are more reactants than products at equilibrium. Therefore, to increase the rate of product formation, we can increase the concentration of reactants to push the reaction in the forward direction. If the concentration of a reactant (on the left) is increased, the equilibrium position moves in the direction away from this reactant, and so more of the products are produced (on the right).
SC12a
Describe how changing the temperature, pressure and concentration all affect the relative amount of substances in an equilibrium mixture.
Temperature: An increase in temperature will cause the reaction to shift towards the endothermic reaction, which absorbs heat. This will decrease the concentration of the products and increase the concentration of the reactants if the forwards reaction is exothermic, reducing the overall products. This will increase the concentration of the products and decrease the concentration of the reactants if the forwards reaction is endothermic, increasing the overall products.
Concentration: Changes in the concentration of reactants and products can also affect a reaction at equilibrium. If the concentration of a reactant is increased, the reaction will shift towards the side with the product to counteract the increase.
Pressure: When the pressure of a reaction is changed, the position of equilibrium will shift. An increase in pressure will increase the rate of reaction, so the time taken to reach equilibrium is reduced. This is because the gas molecules are closer together, so there are more frequent collisions. Gaseous reactions will be affected by changes in pressure, but reactions with solids and liquids will not. Pressure is affected by the number of molecules. The more molecules/ moles of a gas there are, the higher the pressure.
