I/GCSE Chemistry - Rates and Equilibrium (Part 2)

Welcome to I/GCSE Chemistry - Rate and Equilibrium (Part 2)

• Catalysts reduce energy costs and change reaction rates.
• They are unchanged chemically at the end of the reaction, so is reusable.
• There are specific catalysts.
• Many used in industry involve transition metals and many are used as a gauze, pellet, or powder to give a big SA:V.

• Catalysts don't increase collision frequency or make collisions more energetic
• Instead they increase reaction rate by providing alternate reaction pathways to the products, with a lower activation energy than without catalysts.
•  A higher proportion of reactant particles have sufficient energy to react so the frequency of effective collisions rise.

• Catalysts are often expensive, precious metals since they are most effective for some reactions.
• Catalysts are cheaper and help the environment since it reduces the higher temperatures and pressures needed (which are used to increase reaction rates instead of catalysts), which involve burning fossil fuels.
• Catalysts conserve non-renewable resources and combat climate change by stopping more carbon dioxide from being used, but catalysts can become 'poisoned', not working anymore due to impurities in the reaction mixture mixing with it.

In the content of I/GCSE Chemistry, products react together to make the original, and the reaction can go in both directions

Examples:

1. Red litmus changing to blue litmus,
2. Salts and their water of crystallisation
3. Heating ammonium chloride, which breaks down upon heating to form NH3 and HCl (g). Upon cooling down they react again to reform ammonium chloride.

• In reversible reactions the same amount of energy transferred to the surroundings is the same as the energy transferred back.
• The same amount of energy is absorbed.
• Copper sulfate is hydrated and heating copper (II) sulfate crystals produces white anhydrous white copper (II) sulfate, which is endothermic, but when you add water again, hydrated copper (II) sulfate forms again, which is exothermic.
• Soak filter paper in cobalt (II) chloride and allow to dry.
• The blue paper made is cobalt (II) paper, which turns pale pink when water is added.

• A closed system is when no matter can enter or exit.
• As the concentration of products builds up, the rate at which they react to reform the original rises.
• The forward reaction rate decreases because the reactants' concentration decrease from its original minimum value.
• Eventually both forward and reverse reactions occur at the same rate but in opposite directions, and when this happens, the reactants make products at the same rate the products make reactants, so overall there is no change in the amount of products and reactants.
• The reaction has reached equilibrium.

• In the content of I/GCSE Chemistry, the relative amount of reactants and products in a reacting mixture at equilibrium can be changed - Le Chatelier's Principle.
• Whenever a change in conditions is introduced, its position changes to cancel out the change.
• It is important for chemists to find conditions giving out as much of the products as possible in as short time as possible, but other factors like economic and social ones must be considered.

• If a reversible reaction involves changing numbers of gas molecules altering pressure can affect equilibrium too. By doing this you change the amount of products made.
• If the forward reaction has more molecules, a pressure increase decreases the amount of products made but if the pressure decreases, there's an increase in the amount of products made.
• If the reverse reaction has fewer gas molecules, a pressure increase increases the amount of products made, and a pressure decrease decreases product amount.
• When the amount of gas molecules is equal on either side, changing pressure has no effect on the mixture's composition but it'll change the rate of both reactions by the same amount.
• If it is in a closed system, the relative amount of products and reactants depends on temperature.
• If the forward reaction is exothermic, an increase in temperature decreases the amount of products made, and the opposite
• If the forward reaction is endothermic, an increase in temperature increases the amount of products made, and the opposite.

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Written by Bryant Wong (Chemistry)

Photo reference

1. expii.com, https://www.expii.com/t/catalysts-enzymes-overview-examples-10085
2. sliderbase.com, http://www.sliderbase.com/spitem-94-1.html
3. educationquizzes.com, https://www.educationquizzes.com/gcse/chemistry/rates-of-reaction-1/