Chemical Equilibria (Kc) and Kp Flashcards
Where will equilibrium shift if reactant is added?
To the RIGHT.
Where will equilibrium shift if product is added?
Shift to the LEFT.
Where will equilibrium shift if reactants are reduced?
Shift to the LEFT.
Where will equilibrium shift if products are reduced?
Shift to the RIGHT.
Where will equilibrium shift if Temperature is increased?
Moves in the Endothermic direction.
Where will equilibrium shift if Temperature is decreased?
Moves in the Exothermic direction.
Where will equilibrium shift if Pressure is increased?
Moves to side with fewer molecules.
Where will equilibrium move if Pressure is decreased?
Moves to the side with more molecules.
Where will equilibrium shift if Volume is increased?
- Pressure decreases
- Moves to side with more molecules
Where will equilibrium shift if Volume is decreased?
- Pressure increases
- Moves to the side with fewer molecules
State where equilibrium is reached on an equilibrium graph.
- where two lines meet and plateau.
What is the definition of dynamic equilibrium?
- The concentrations of the reactants and products remain constant
- The rate of the forward reaction = rate of the reverse reaction
How is a dynamic equilibrium reached? Use reaction rates in your answer.
- At the start of the reaction the forward reaction is fast and the backward reaction is slow
- The backward reaction then speeds up as the forward reaction slows down
- The rate of the forward reaction becomes the same as the rate of the backward reaction
State a condition for a reaction in equilibrium
· Closed system
State Le Chatelier’s principle?
The position of equilibrium will shift to oppose the change.
How to answer Qs if one of the following conditions are changed:
- the TEMPERATURE
- the PRESSURE or VOLUME of the container
- the CONCENTRATION of a reagent
1) STATE THE ANSWER (Yield of X increases/Kp decreases)
2) MAKE A STATEMENT CONCERNING THE CONDITION WHICH HAS BEEN CHANGED (e.g. The forward reaction is endothermic/ There are fewer moles of gas on the RHS)
(1) STATE THAT THE POSITION OF EQUILIBRIUM SHIFTS TO THE RIGHT OR LEFT……..TO OPPOSE THE CHANGE IN CONDITION
What happens to equilibrium when Pressure is changed but there are equal amounts of molecules on either side?
If there were equal number of moles of product and reactant, then changing the pressure would not affect the position of equilibrium.
A catalyst is a substance that speeds up the rate of reaction by providing an alternative reaction pathway with a lower activation energy.
When a catalyst is added to a reversible reaction….
…..the rate of both the forward and reverse reactions increases equally
· there is no change to the position of the equilibrium
· dynamic equilibrium is reached faster.
Why does a catalyst not affect the position of equilibrium?
Catalysts increase the rate of the forward and backward reactions equally.
Why are catalysts added to the Haber process, which is a reversible reaction that produces ammonia?
To reduce the time taken to reach dynamic equilibrium
Compromise conditions are necessary in Haber process because….
…. higher pressures would be too expensive
· 450’C gives a good yield in a fast time
What is the expression for Kc?
Kc = [products]/[reactants]
How can the units for Kc be worked out?
Total molecules of products - Total molecules of reactants
Multiply that number by mol dm-3
How can a known Kc be used to find out one of equilibrium concentration?
The Kc equation can be rearranged.
If Kc is greater than 1…
- then there are more products than reactants at equilibrium and the equilibrium is shifted to the right.
If Kc is less than 1…
- there are more reactants than products at equilibrium and the equilibrium has shifted to the left.
If Kc is exactly 1…
- then the concentration of products is equal to the concentration of reactants.
What is the only condition that can change value of Kc?
Temperature.
You can find Kc from the concentrations of reactants and products at equilibrium using the following process…
1- Initial amounts of each product or reactant
2- Change in each reactant
3- Equilibrium number of moles for each product and reactant
4- Equilibrium concentration of each reactant (mol dm-3)
5- Kc expression (and calculation)
6- Units
Kp expression
Partial pressure of Products/Partial Pressure of Reactants
If Kp is greater than 1…
- it means the equilibrium is towards the right hand side (i.e. more products than reactants).
If Kp is less than 1…
- it means the equilibrium is towards the left hand side (i.e. more reactants than products).
If Kp is exactly 1…
it means the equilibrium is in the middle (i.e. equal amounts of products and reactants).
Which is the only condition that can cause a change in Kp?
Temperature.
A range of different calculations which involve the Kp expression. These include:
Initial mol
Change
Equilibrium moles
Mol Fraction
Partial Pressure
How can you calculate Partial Pressure?
Mole Fraction x Total Pressure
How can you calculate Mole Fraction
No. of moles of Gas A in the mixture/ Total No. of moles of all gases
What is meant by Compromise Temperature?
Balance between rate and yield.
