# Partial pressure and KP

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• Created by: Hindleyc
• Created on: 22-01-19 22:32
What must equilibrium reactions be in?
A closed system - nothing can get in/out
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What are the forward and reverse reaction rates for a reaction in equilibrium ?
Equal
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What does the conc of reactants and products do?
Remain constant for a reaction in equilibrium
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What does a catalyst do to the position of equilibrium?
Doesn't alter the position of equilibrium because it inc the rate of the forward and reverse reactions equally - enables reactions to reach equilibrium more quickly-reduces time taken
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What does le chateliers principle state about a reaction in dynamic equilibrium
Will shift the position of E to oppose any change imposed upon it
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When will Kc values change
If temp of system changes
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So pressure and conc?
Change it for ALL chemicals so doesn't change KC
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What does Kc take into account
No. moles(power)
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When is E reached
When conc are constant
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If Kc=1
POE middle
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If KC>1
POE Right(more p than r)
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If Kc< 1
POE left- reverse rxn favoured
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What a homogenous equilibrium
Contains E species that all have the same state or phase eg gaseous
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Whats a heterogenous equilibrium
Contains species that are in different phases eg solid and gas
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What is the conc of solids and liquids in a heterogenous system
Almost constant therefore we omit them from the kc expression- accounted for by overall equilibrium constant
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Order for working out KC from rxn
Initial mol, Change, Eq mol, Eq conc, KC expression, Unit
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Experimental model answer for determining the value of kc
In conical flask mix Xmol of A and Xmol of b, add catalyst if needed to flask, add acid catalyst to diff false as a control, Stopper in both flasks and leave to reach equilibrium,
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Next
carry out titrations on equilibrium mixture using standard solution of NaOH then repeat with control to determine the amount of acid catalyst that had been added
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What do you do for a reaction that contains gases ?
An alternative equilibrium expression can be set up using the partial pressure of the gases instead of conc
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Partial pressure of a gas in a mixture
Pressure that the gas would have if it alone occupied the volume occupied by the whole mixture(if in container on its own)
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What if a mixture of gases contains 3 different gases?
Total pressure will equal the 3 partial pressures added together
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eqn
p=p1+p2+p3
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What does each gas contribute to and what type of equilibrium
Total pressure- homogenous
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Why is this?
When gases are held within a container the collisions of the gas particles on the inside walls of the container causes pressure
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Partial pressure of gas 1=
Mole fraction of gas 1 X total pressure - should all add up to toal
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mole fraction
Number of moles of a gas/ total number of moles of all gases - should add up to 1
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Brackets
not square
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kp=
(pC)(pD)/(pA)(pB)
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What do you only include in the Kp expression
Gases- ignore S L AQ
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How do you work out units
Put units of pressure into kp expression and cancel
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Calculation order
Initial mol, Change, Eq mol, Mol fraction, Partial pressure
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If Kp>1
E towards right- favours Product
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kp<1
E towards left - favours reactants
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Kp=1
E middle
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What are the only conditions that can cause the value of Kp to cahnge
change in temp
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What if heterogenous
Make Kp expression only contain gaseous substances and any substances with another state is left out
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What does a catalyst do
Affect rate of attainment of an Equilibrium but doesn't affect value of EC
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The larger the Kp
The greater amount of products
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If Kp small
POE favours the reactants
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Kc and Kp only change with
Temperature - doesn't change if pressure or conc altered
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Catalysts effect on kp or Kc
None
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Effect of temperature
Both POE and value of KP/KC will change if temp is altered
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Temp inc
Favour endo
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If moving E to left
Kp smaller
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Effect of pressure
POE will change if pressure altered but value of KP will stay constant as KP only varies with temp
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Exam technique
State answer, make statement concerning the condition which has been changed, state POE shifts
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## Other cards in this set

### Card 2

#### Front

What are the forward and reverse reaction rates for a reaction in equilibrium ?

Equal

### Card 3

#### Front

What does the conc of reactants and products do?

### Card 4

#### Front

What does a catalyst do to the position of equilibrium?

### Card 5

#### Front

What does le chateliers principle state about a reaction in dynamic equilibrium

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