AC6: Equilibria
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What are the 3 characteristics of a dynamic equilibrium
-The rate of the forward reaction and backward reaction is equal, so the concentration of substance in the mixture do not change - Equilibrium can only be established if the system is closed - If a system us at equilibrium, the temperature, pressure of concentration of each substance remain constant
What is the general formula of Kc
Kc = [Product] x [Product] / [Reactant] x [Reactant] And always remember the molar number infront of the substance in the equation you put to the power e.g 2NH3 = [NH3] ^2
What is the only factor that will change the value of Kc
Temperature
What are the units of Kc
Dependent on the reaction, just cancel the equation to calculate the units
List 3 ways to follow change in concentration
• Change in absorption of light, if one of the substances is coloured • Change in pH, if one of the reactants is acid or alkaline • Titration of one of the reactants
When you are given a question about equilibrium but not given the moles of the substances at equilibrium what must you do first before calculating Kc
Find moles at start of reaction Find moles at equilibrium Find change in the moles Change in moles will be proportional to all the substances in the reaction The calculating concentration to sub into the Kc equation
If Kc is larger, what does that mean about the position of equilibrium
Lies over to the right
What does Le Chatelier’s Principle states will happen to position of equilibrium when temperature increases
It’ll shift in the endothermic direction
When the temperature increases, the equilibrium shifts in the endothermic direction, what does that do to the equilibrium constant
Changes it’s value
If the equilibrium shifts left, what effect does that have on Kc
Kc gets smaller since the number on the bottom lien gets bigger
If the equilibrium shifts right, what effect does that have on Kc
Kc gets bigger since the top line of the equation gets bigger
Does pressure change the value of Kc
No
When the pressure changes in an equilibrium, why does the equilibrium shift to the side with the fewer moles of gas
To maintain concentrations of both reactants and products that are consistent with Kc
What is the effect of a catalyst on the position of equilibrium and the value of Kc, and why
There is no effect on either since a catalyst increases the rate of both the forward and backward reaction by the same factor
When the Kc is larger than the correct Kc, so the reaction isn’t a equilibrium, what must happen to correct this
The top line needs to decrease and the bottom line needs to increase to decrease the value of Kc. So the equilibrium shifts left so more reactants are formed than products
When there are multiple gases in a container, how they exert their pressures
Independently
All the partial pressure in a container must add to what
The total pressure of the container
What is the general formula for Kp
Partial pressure of products multiplied together / the partial pressure of the reactants multiplied together
If Kp is a big number, where is the equilibrium positioned
To the right
If Kp was a small number, where is the equilibrium positioned
To the left
What are the units Kp
Depends on the equation, so cancel all of the units from the reaction , just like Kc, the unit will kPa or atm minus etc.
How do you calculate the mole fraction of each gas in the equation, when given the moles of all the gases
Moles of gas A / Moles of all the gases
What should all the mole fractions add up to
One
How do you find the partial pressure of a gas after finding the mole fraction of that gas
mole fraction x total pressure