Chapter 19 Flashcards
What is the mole fraction?
the mole fraction is the fraction of the total number of moles that each chemical in a reaction is responsible for
What is partial pressure?
Partial pressure is the part of the total pressure that each chemical in a reaction is responsible for.
Its also the pressure a gas exerts in a mixture of gases in a container.
What is the symbol for partial pressure?
p
What is the total pressure?
The sum of the partial pressures.
How can you work out the partial pressure of a gas?
partial pressure = total pressure x mole fraction
How do you work out the mole fraction of a gas?
Number of moles of that gas / total number of moles of gas
How do you calculate equilibrium quantities? (using ICE technique)
initial concentration
change in concentration
equilibrium concentration
Use the stoichiometric equation and fill in the gaps with the information you are given.
What is the equilibrium constant?
Kc
What are the units for Kc + how do we work them out?
To work out the units of Kc you cancel common units from the products/reactants.
if all cancel out there are no units
if after cancelling you get mol dm-3/1 then you will get the units moldm-3
if after cancelling you get 1/moldm-3 then you get the units dm3mol-1
How do you write the Kc expression?
[products]/[reactants]
What does homogeneous equilibria mean?
Contains equilibrium species of all the same state/phase.
What does heterozygous equilibria mean?
Contains equilibrium species of different states/phases.
How do you write the Kp expression?
Kp = p(A) p(B) / p(C) p(D)
What state must reactants be in to be in the kp expression?
Only gases are included
When does Kp change?
When the temperature changes
How do you work out Kp (step by step)?
find out the mole fractions of the gases present
their partial pressures
the Kp expression
the value of Kp
What are the units for Kp?
Kpa-1/Pa-1/atm-1
How does Le Chateliers Principle work?
if a change is made to a system in dynamic equilibrium, the position of the equilibrium moves to counteract this change
How does equilibrium shift with temperature change?
increase in temp- Moves in the endothermic direction
decrease in temp- Moves in the exothermic direction
What is the effect of changing temperature on the value of Kc?
For a reaction that is exothermic in the forward direction, increasing the temperature pushes the equilibrium from right to left. (towards endothermic side)
Therefore, the value of Kc will decrease as the ratio of [ products ] to [ reactants ] decreases
Conversely, if the temperature is raised in an endothermic reaction, the value of Kc will increase
What is the effect of changing temperature on the value of Kp?
For a reaction that is exothermic in the forward direction, increasing the temperature pushes the equilibrium from right to left (towards the endothermic side)
Therefore, the value of Kp will decrease as the ratio of [ products ] to [ reactants ] decreases
Conversely, if the temperature is raised in an endothermic reaction, the value of Kp will increase
What is the effect of changing pressure on the value of Kc?
No effect as it doesn’t involve gases.
How does equilibrium shift when pressure changes?
increase in pressure- Shifts in the direction with the fewer number of moles of gas to decrease pressure.
decrease in pressure- Shifts in the direction that has the larger amount of moles of gas to increase pressure.
What is the effect of changing pressure on the value of Kp?
The value of Kp is not affected by any changes in pressure.
Changes in pressure cause a shift in the position of equilibrium to a new position which restores the value of Kp
this is the same for changes in concentration and the Kc value.
How does a catalyst affect the value of Kc/Kp?
If all other conditions stay the same, they are not affected by a catalyst.
A catalyst speeds up both the forward and reverse reactions at the same rate so the ratio of [ products ] to [ reactants ] remains unchanged. They only cause a reaction to reach equilibrium faster.
