1.6 Equilibria Flashcards
If the forward reaction of a reversible reaction is exothermic, what will the backwards reaction be
Endothermic
What is dynamic equilibrium
When the rate of the forward reaction is equal to the rate of the backward reaction.
What is the only way in which dynamic equilibrium can occur
In a closed system.
What is a closed system
A system in which no substances can enter or leave during a reaction, however energy can be transferred.
What is Le Chatelier’s principle
When the conditions of a reaction at equilibrium are changes, the system will shift to oppose the change.
Why is Le Chatelier’s principle useful
It can be used in industry to maximise the yield of a reaction.
What are 4 factors looked at when using Le Chatelier’s principle
- Changes in temperature
- Changes in pressure
- Changes in concentration (of reactants or products)
- Presence of a catalyst
How does increasing the temperature affect equilibrium
- Increasing the temperature will cause the equilibrium to shift in the endothermic direction
- This is because an increase in the endothermic reaction will increase the amount of energy used, causing the temperature to decrease
- The system has therefore moved to oppose the change in temperature
How does increasing the pressure affect the equilibrium
- Increasing the pressure causes the equilibrium to shift to the side with fewer moles of gas
- This will help to release the build up of pressure
How does decreasing the pressure affect the equilibrium
Decreasing the pressure will cause the equilibrium to shift to the side with more moles of gas, as pressure has been lost.
How does increasing the concentration of reactants affect the equilibrium
- The equilibrium will shift to the right, causing more products to be made
- This is because there are more molecules to react, so more product can be produced
What does the equilibrium constant (Kc) show
It indicates the position of equilibrium for a reaction at a certain temperature.
How do you calculate the Kc value for a reaction
Kc is the concentration of the products to the power of their moles divided by the concentration of reactants to the power of their moles.
How do you find the units for a Kc value
- Sub the units for concentration into the Kc expression for that reaction
- Sometimes the units cancel out, so there are none
What affects the Kc value
Kc is only affected by temperature as the equilibrium position results in different concentrations of reactants and products.
What can you tell about the position of equilibrium if the Kc value > 1
The equilibrium lies to the right (there are mainly products).
What can you tell about the position of equilibrium if the Kc value < 1
The equilibrium lies to the left (there are mainly reactants).
What can you tell about the position of equilibrium if the Kc value is close to 1
The equilibrium is fairly central (there are similar amounts of reactants and products).
