[3.1.6] Chemical Equilibria, Le Chatelier’s Principle & K꜀ Flashcards
Chemical Equilibria & Le Chatelier's Principle and Equilibrium Constant K꜀ for Homogeneous Systems.
What are the two features of a dynamic equilibrium?
- Forward and backward reactions are occurring at equal rates.
- The concentrations of reactants and products stay constant.
What is Le Chatelier’s principle?
Le Chatelier’s principle states that if an external condition is changed, the equilibrium will shift to oppose the change (and try to reverse it).
What is the effect of increasing temperature on equilibrium?
If temperature is increased the equilibrium will shift to oppose** this and move in the endothermic direction to try to reduce the temperature by absorbing heat.
What is the effect of decreasing temperature on equilibrium?
If temperature is decreased the equilibrium will shift to oppose this and move in the exothermic direction to try to increase the temperature by giving out heat.
Low temperatures may give a higher yield of product but will also result in what?
Slow rates of reaction so often a compromise temperature is used that gives a reasonable yield and rate.
What is the effect of increasing pressure on equilibrium?
Increasing pressure will cause the equilibrium to shift towards the side with fewer moles of gas to oppose the change and thereby reduce the pressure.
What is the effect of decreasing pressure on equilibrium?
Decreasing pressure will cause the equilibrium to shift towards the side with more moles of gas to oppose the change and thereby increase the pressure.
If the number of moles of gas is the same on both sides of the equation, what effect will changing pressure have on the position of equilibrium?
If the number of moles of gas is the same on both sides of the equation, then changing pressure will have no effect on the position of equilibrium.
Increasing pressure may give a higher yield of product and will produce a faster rate, but what are the downsides of increasing pressure?
- Industrially high pressures are expensive to produce.
- High electrical energy costs for pumping the gases to make a high pressure.
- Equipment is expensive to contain the high pressures.
What is the effect of increasing the concentration of OH⁻ ions on the equilibrium in the reaction below?
If you added H⁺ ions, how would it affect the equilibrium?
- Increasing the concentration of OH⁻ ions causes the equilibrium to shift to oppose this and move in the forward direction to remove and decrease the concentration of OH⁻ ions.
- The position of the equilibrium will shift towards the right, giving a higher yield of I⁻ and IO⁻.
- The colour would change from brown to colourless.
ADDING H⁺ IONS
- Adding H⁺ ions reacts with the OH⁻ ions and reduces their concentration.
- So the equilibrium shifts back to the left giving brown colour.
What is the effect of catalysts on equilibrium?
- Catalysts have no effect on the position of equilibrium, but it will speed up the rate at which the equilibrium is achieved.
- It does not affect the position of equilibrium because it speeds up the rates of the forward and backward reactions by the same amount.
Describe and explain the conditions in the Haber process.
HABER PROCESS
- Temperature = 450°C
- Low temperature gives good yield, but slow rate: compromise temperature used.
- Pressure = 200-1000 atm
- High pressure gives good yield and high rate.
- Too high a pressure would lead to too high energy costs for pumps to produce pressure and too high equipment costs to have equipment that can withstand high pressures.
- Catalyst = iron
- Catalysts speed up the rate, allowing a lower temperature to be used and hence lower energy costs.
- Catalyst has no effect on the position of equilibrium.
- Recycling unreacted reactants back into the reactor can improve the overall yield.
Describe and explain the conditions in the contact process.
CONTACT PROCESS
- Temperature = 450°C
- Low temperature gives good yield, but slow rate: compromise temperature used.
- Pressure = 1-2 atm
- High pressure only gives a slightly better yield and high rate.
- Too high a pressure would lead to too high energy costs for pumps to produce pressure and too high equipment costs to have equipment that can withstand high pressures.
- Catalyst = V₂O₅
- Catalysts speed up the rate, allowing a lower temperature to be used and hence lower energy costs.
- Catalyst has no effect on the position of equilibrium.
- Recycling unreacted reactants back into the reactor can improve the overall yield.
Describe and explain the conditions in the production of methanol from CO.
PRODUCTION OF METHANOL FROM CO
- Temperature = 400°C
- Low temperature gives good yield, but slow rate: compromise temperature used.
- Pressure = 50 atm
- High pressure only gives a slightly better yield and high rate.
- Too high a pressure would lead to too high energy costs for pumps to produce pressure and too high equipment costs to have equipment that can withstand high pressures.
- Catalyst = chromium & zinc oxides
- Catalysts speed up the rate, allowing a lower temperature to be used and hence lower energy costs.
- Catalyst has no effect on the position of equilibrium.
- Recycling unreacted reactants back into the reactor can improve the overall yield.
- If the carbon monoxide used to make methanol in this process was extracted from the atmosphere then it could be classed as carbon neutral.
- It would only be carbon neutral, however, if the energy required to carry out the reaction was not made by the combustion of fossil fuels.
- The term carbon neutral refer
- It would only be carbon neutral, however, if the energy required to carry out the reaction was not made by the combustion of fossil fuels.
Describe and explain the conditions in the hydration of ethene to produce ethanol.
HYDRATION OF ETHENE TO PRODUCE ETHANOL
- Temperature = 300°C
- Low temperature gives good yield, but slow rate: compromise temperature used.
- Pressure = 1-2 atm
- High pressure only gives a slightly better yield and high rate.
- Too high a pressure would lead to too high energy costs for pumps to produce pressure and too high equipment costs to have equipment that can withstand high pressures.
- High pressure also leads to **unwanted polymerisation of ethene to poly(ethene*.
- Catalyst = concentrated H₃PO₄
- Catalysts speed up the rate, allowing a lower temperature to be used and hence lower energy costs.
- Catalyst has no effect on the position of equilibrium.
- Recycling unreacted reactants back into the reactor can improve the overall yield.
What is the equation for the equilibrium constant, K꜀?
Write an expression for K꜀ for the equation below.
Work out the units of K꜀ for the expression below.
Write an expression for K꜀ for the equation below and the units too.
In this equilibrium below, which is exothermic in the forward direction, what would be the effect of increasing temperature on the position of equilibrium and K꜀?
- If the temperature is increased, the reaction will shift to oppose the change and move in the backwards endothermic direction.
- The position of equilibrium shifts left.
- The value of K꜀ gets smaller as there are fewer products.
In this equilibrium below, which has fewer moles of gas on the product side, what would be the effect of increasing pressure on the position of equilibrium and K꜀?
- If the pressure is increased, the reaction will shift to oppose the change and move in the forward direction to the side with fewer moles of gas.
- The position of equilibrium shifts right.
- The value of K꜀ stays the same as only te,perature changes the value of K꜀.
