Equillibria 1 Flashcards
What is an equilibrium mixture
The mixture of reactants and products achieved when a reaction is at equilibrium.
The proportion of each compound remains constant-this is the equilibrium mixture.
What is dynamic equilibrium
The point where the rates of the forwards and backwards reactions are equal.
What four conditions describe an equilibrium
1) Equilibrium can only be reached in a closed system (one where the reactants and products can’t escape). The system does not have to be sealed. Eg a beaker is fine as long as none of the reactants/products could evaporate.
2) Equilibrium can be approached from either direction, starting with either reactants or products, and the final equilibrium position will be the same (as long as conditions remain constant)
3) Equilibrium is a dynamic process. It is reached when the rates of the forwards and backwards reaction are equal.
4) You know that equilibrium has been reached when the macroscopic properties of the system do not change with time. These are properties such as density, concentration, colour and pressure.
What are macroscopic properties (dynamic equilibrium)
Properties that do not depend on the total quantity of matter
What are some examples of macroscopic properties
Density, concentration, colour and pressure
What is Le Chateliers principle
If a system at equilibrium is disturbed, the equilibrium moves in the direction that tends to reduce the disturbance.
What happens to a reversible reaction at equilibrium if the concentration of a reactant is increased
The position of equilibrium shifts to the right (forwards/product direction) in order to counteract the change.
What happens to a reversible reaction at equilibrium if the concentration of a product is increased
The position of the equilibrium moves to the left (backwards/reactant) direction in order to counteract the change
What happens to a reversible reaction at dynamic equilibrium when pressure is increased
- Increasing pressure causes the equilibrium to move to decrease pressure
- This means it shifts towards the side of the reaction with fewest moles of gas.
- This is because gas molecules exert pressure, so the less there are, the lower the pressure.
- This counteracts the change in conditions.
What happens to a reversible reaction at equilibrium when pressure is decreased
- The system tries to oppose the decrease in pressure by increasing it.
- It does this by shifting towards the side of the reaction with the most moles of gas.
- This is because gas molecules exert pressure, so the more there are, the higher the pressure.
- This counteracts the change in conditions.
When will changing the pressure have no effect on the position of equilibrium
When none of the products or reactants are gases and when there are the same number of moles of gas either side of the reaction.
What will happen to the position of equilibrium if temperature is increased
- The system works to counteract the increase in temperature by decreasing it.
- So it shifts in the endothermic direction
What will happen to the position of equilibrium if temperature is decreased
- The system works to counteract the decrease in temperature by increasing it.
- So it shifts in the exothermic direction.
How does the use of a catalyst affect the position of equilibrium
- Catalysts have no affect on the position of equilibrium
- They lower the activation energy required for the reaction to occur, but this affects the forwards and backwards reactions equally.
- They do, however, allow an equilibrium to be reached more quickly.
What does Kc represent
The equilibrium constant Kc