7. Equilibrium Flashcards
What are the features of dynamic equilibrium?
- Requires a closed system
- Forward and reverse reactions are at the same rate
- Forward and reverse reactions concentrations remain constant.
Define ‘yield’.
The amount of product in the equilibrium mixture, usually expressed as a percentage.
Define a ‘homogeneous system’.
All reactants, products and catalysts are in the same phase.
Define a ‘heterogeneous system’.
One of the chemicals is in a different state.
State Le Chatelier’s principle.
- High pressure favours the side with the fewest moles of gas.
How do catalysts affect equilibrium?
They don’t because they increase the rate of both reactions equally.
What happens if you remove a substance from the equilibrium mixture?
The position of equilibrium will shift to replace the substance.
What does Kc refer to?
The concentration of reactants.
What does a large Kc mean?
Lots of products are formed.
What is Kc affected by?
Only temperature and stochiometric coefficients.
Kc= ?
[products]/ [reactants]
What does it mean if Kc>1?
The products are favoured over reactants.
What does it mean if Kc<1?
The reactants are favoured over the products.
What does it mean if Kc=1?
The mixture contains appreciable amounts of both products and reactants.
What is the effect on Kc if the coefficient is halved?
√Kc
What is the effect on Kc if the coefficient is doubled?
Kc²
What is the effect on Kc if the equation is reversed?
1/Kc
What is the effect on Kc if the equations are added together?
The Kc values are added together.
How does an increase in temperature affect an exothermic forward reaction?
- The equilibrium will shift in the endothermic direction (to the left)
- Yield of products decreases
How does an increase in temperature affect an endothermic forward reaction?
- The equilibrium will shift in the endothermic direction (to the right)
- Yield of products increases
What is the reaction quotient?
When a system is not at equilibrium, the ratio of concentrations of products and reactants differs from the Kc value.
What does it mean if Q>K?
There are less reactants and more products than needed for equilibrium, so the reverse reaction will be favoured.
What does it mean if Q<K?
The mixture contains more reactants and less products than needed for equilibrium, so the forward reaction is favoured.
What does it mean if Q=K?
Equilibrium has been achieved so the rate of forward and backward reaction will be the same.
What is the equation that links K and Gibbs Energy?
∆G= -RT lnK
What does a negative ∆G value for a reaction indicate?
- The reaction is feasible/ spontaneous
- The equilibrium concentration of the products is greater than the equilibrium concentration of the reactants.
- The value of the equilibrium constant will be greater than 1.
