Starter quiz
- Which of the following statements for a dynamic equilibrium are correct?
- The concentrations of reactants and products remain constant. ✓
- The forward and backward reactions occur at the same rate. ✓
- Occurs in a closed system, where matter cannot enter or leave. ✓
- Requires a catalyst to get started, and high pressure and temperature.
- Requires a reversible reaction, with conditions feasible for both directions. ✓
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- When ammonia is removed during the Haber process, which of the following changes occur to the dynamic equilibrium?
- The backward reaction no longer takes place. ✓
- The concentration of product is changed – all of the ammonia is removed. ✓
- The reactants, hydrogen and nitrogen gas, escape into the environment.
- The system is opened so that matter can leave. ✓
- The temperature is lowered so the forward reaction slows down a lot. ✓
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- Match the following key terms to their definition.
- dynamic equilibrium⇔a state where the forward and backward reaction rates are equal ✓
- reaction rate⇔the speed of chemical reactions: amount of matter used/made over time ✓
- reaction conditions⇔factors including temperature and pressure that affect reaction rate ✓
- concentration⇔the amount of reactant or product in a defined volume of space ✓
- The Haber process requires iron and the Contact process requires vanadium. These substances speed up the reactions without being used up or changed. Different reactions require different ______.
- 'catalysts' ✓
- Which of the following graphs would be an appropriate representation of rate of reaction vs. time, for a dynamic equilibrium?
- Many reactions in industrial chemistry are reversible reactions that reach equilibrium. 100% of the desired product can never be achieved. Which of the following issues may be encountered?
- By-products could be waste but they can sometimes be made profitable. ✓
- Gaseous reactants/products can be difficult to contain for reuse or removal. ✓
- High pressure and temperature require considerable/expensive safety measures. ✓
- Remaining reactants can be hard to isolate from the desired product. ✓
- Unreacted reactants are economically and environmentally disadvantageous. ✓
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Exit quiz
- One mole of any gas occupies the same ______ under the same temperature and pressure conditions.
- 'volume' ✓
- Changing the number of particles of gas in a fixed volume will change the conditions. Adding gaseous matter changes the ______ as there are more particles colliding with the walls of the container.
- 'pressure' ✓
- Consider the reaction CO(g) + 2H₂(g) ⇌ CH₃OH(g). What happens when the pressure is increased?
- equilibrium doesn't change because the number of atoms are equal on both sides
- the equilibrium shifts to the left, where there are more gas molecules
- the equilibrium shifts to the right, where there are fewer gas molecules ✓
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- Consider: Fe₂O₃(s) + 3CO(g) →2Fe(l) + 3CO₂(g). It would be easy to let the by–product escape, to shift the equilibrium to get the desired product, Fe. Why is this undesirable?
- CO would also escape, and the reaction would stop. ✓
- CO₂ is a greenhouse gas, which we want to avoid putting in the atmosphere. ✓
- The reaction would cool down and the iron product would become solid.
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- Why does temperature affect the equilibrium position?
- Because a reversible reaction has an exothermic and an endothermic direction. ✓
- Because reactions slow down or speed up when temperature is changed.
- Because temperature affects the rate of reaction.
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- Match the following key terms to their definitions.
- catalyst⇔a chemical which speeds up the rate at which equilibrium is achieved ✓
- equilibrium position⇔the relative concentrations of reactants and products at equilibrium ✓
- Le Chatelier’s principle⇔the equilibrium position shifts to counteract a change in conditions ✓
Worksheet
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Lesson Details
Key learning points
- Catalysts, pressure, temperature & concentration of solutions can affect equilibrium position of a reversible reaction.
- If the conditions of a reversible reaction are changed, the equilibrium will move to counteract that change.
- A catalyst increases the rate at which equilibrium is achieved.
- Increasing temperature increases the rate of both reactions; equilibrium shifts in favour of the endothermic reaction.
- Increasing the concentration or pressure of a substance increases the rate of reaction; equilibrium shifts in response.
Common misconception
At dynamic equilibrium the reactions stop; increasing pressure always shifts equilibrium to one side; increasing temperature always favours product formation; catalysts shift the equilibrium position.
At dynamic equilibrium, reactions continue at equal rates. Pressure shifts equilibrium only if gas molecule numbers differ. Temperature favours the endothermic direction when increased. Catalysts speed up reaching equilibrium but don't shift it.
Keywords
Le chatelier’s principle - states that if a dynamic equilibrium is disturbed by changing the conditions, the equilibrium position ‘shifts’ to counteract the change.
Dynamic equilibrium - occurs in a closed system when the forward and backward reactions of a reversible chemical reaction occur at the same rate; and the concentrations of reactants and products remain constant.
Equilibrium position - refers to the relative concentrations of reactants and products in a reversible reaction at equilibrium.
Reaction rate - is the speed with which a chemical reaction takes place, measured by the amount of a reactant used or amount of product formed in a given time.
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