GCSE equilibrium model answers

A higher temperature increases the of reaction because molecules have more energy and move faster. This leads to more frequent collisions, and more of these collisions exceed the required energy to be successful.

However, a higher temperature decreases the equilibrium of ammonia. This is because the reaction to make ammonia is , so the shifts to the left in the direction to oppose the change.

A is used to speed up the reaction but it does not affect the final yield. This is because it speeds up both the forward and reactions by the same amount.

• Higher Pressure (Yield): Increasing the pressure increases the equilibrium yield of sulfur trioxide. This is because there are moles of gas on the product side (2 moles) compared to the reactant side (3 moles), so the equilibrium shifts to the to reduce the pressure.

• Higher Pressure (Rate): The higher pressure increases the rate of reaction, as the gas molecules are closer together, leading to more collisions.

• Lower Temperature (Yield): Decreasing the temperature from 680 °C (Set A) to 425 °C (Set B) further increases the equilibrium yield. As the forward reaction is , a lower temperature causes the equilibrium to shift to the right to release heat and counteract the change.

• The Rate Compromise: Although a lower temperature would normally decrease the reaction rate, this is overcome in Set B by the use of a .

• Catalyst (Rate): The catalyst increases the rate at which equilibrium is reached by providing an alternative reaction pathway with a lower energy.

• Catalyst (Yield): The catalyst affect the position of the equilibrium or the final yield.

Forward Reaction

• Place a sample of , hydrated copper(II) sulfate crystals into a boiling tube and gently with a Bunsen burner.

• Observation: The blue crystals will turn into a powder, and steam will be produced, which may condense into droplets on the cooler part of the tube.

Reverse Reaction

• Allow the white, anhydrous copper(II) sulfate powder to cool completely.

• Carefully add a few drops of to the white powder.

• Observation: The powder will turn again, reforming the hydrated crystals. The boiling tube will also feel hot, showing the reaction is .

Since the original substance can be reformed by adding water to the products, the reaction is demonstrated to be reversible.

• A high temperature of 900 °C the rate of reaction as particles have more kinetic energy, leading to more and more energetic collisions.

• However, the high temperature decreases the equilibrium yield because the forward reaction is exothermic, so the equilibrium shifts to the to absorb the added heat.

• A high pressure of 10 atm increases the reaction rate because the gas molecules are together, increasing collision frequency.

• The high pressure decreases the yield, as the equilibrium shifts to the left, the side with moles of gas (9 moles vs 10 moles), to oppose the pressure increase.

• Using excess air increases the concentration of oxygen, shifting the equilibrium to the to favour the products and therefore increasing the yield.

• Overall, the conditions are a , sacrificing a high yield to achieve an economically fast rate of production.

• The very high temperature (900 °C) makes the reaction happen much faster because it gives the particles lots of energy to move around and into each other with enough force to react.

• However, this high temperature actually means you get less of the final product. Because the reaction releases heat, the reaction tries to cool itself down by going backwards instead.

• The high pressure also makes the reaction faster by squashing all the gas particles closer together, making them collide more .

• But, like temperature, the high pressure also means you get less product. The reaction tries to lower the pressure by going backwards to the side that has gas particles (9 particles on the left vs 10 on the right).

• Adding extra air helps to push the reaction forward to make more , because the reaction wants to use up the extra oxygen that has been added.

• So, these conditions are a . They are chosen to make the reaction happen fast enough to be useful, even if it means you don't get the maximum possible amount of product.

For fun the hint is written to explain what is going on to a 5 year old.