Chapter 19 - Equilibrium Flashcards
How to calculate the units for Kc
- Substitute the units into the expression for Kc.
2. Cancel any common units
What’s a homogeneous Equilibria
All the species in the reaction have the same state or phase.
The Kc expression contains the concentrations of all species.
What’s a heterogeneous Equilibria
Equilibrium species all have different states or phases.
The concentrations of solids and liquids are generally constant, so they are emitted from the Kc expression.
What states are included in the Kc expression?
Only gaseous and aqueous.
What’s the ICE table for calculating the Equilibrium concentration?
I- initial- number of moles given
C- change- reactants have a -x. This is multiplied by the number of moles in the reaction. The products are +x also multiplied.
E- equilibrium change - take away the initial moles from the change. (or add)
Then divide this by the volume given if there is a volume given.
PAG: Determining Kc from experimental results
This reaction is for a carboxylic acid and alcohol.
1. In a conical flash, mix 0.1mol of the carboxylic acid and 0.1mol of the alcohol. Add in 0.05mol of HCl to act as an acid catalyst.
2. Add 0.05mol of HCl to a second conical flask to act as a control.
3. Add a stopper to both.
4. Leave for a week
5. Carry out a titration on the eq. mxiture using a standard solution of NaOH.
6. Repeat with the acid catalyst to give you the number of moles of acid in each.
Then calculate Kc.
Define the mole fraction of a gas
It is the same as its proportion by volume to the total volume of gases in a gas mixture.
Formula for the mole fraction
Mole fraction of A = (number of moles of A)/ total number of moles in a gas mixture.
What is the sum of the mole fractions
1
Define the partial pressure
In a gas mixture, the partial pressure of a gas is the contribution that the gas makes towards the total pressure (P)
Formula for the partial pressure
Partial pressure of A = Mole fraction of A x total pressure (P)
Sum of partial pressures?
Total pressures
Formula for Kp
p (Products) / p (Reactants)
To the power of the balancing number in the equation
Kp only uses what species?
Only uses gases, all other species must be ignored.
What does the value of K show you
The extent of a chemical equilibrium.
If K = 1
Equilibrium sits in the middle
If K = 100
The equilibrium lies in favour of the products
If K = 1 x 10-2
The equilibrium lies in favour of the reactants
What affects the K?
Only the temperature.
In exothermic reactions…
The EC decreases with increasing temperature.
When you increase the temperature, the EC shifts to the side of the endothermic change, so the reactants, and so the equilibrium yield of the products decreases.
In endothermic reactions…
The EC increases with increasing temperature. When you increase the temperature, the EC shifts to the side of the endothermic change, so the products, and so the equilibrium yield of the products increases.
How does changing the concentration and the pressure affect the K?
Doesn’t affect it at all. The system changes the concentration of pressures of certain chemicals only to keep the K constant in the reaction.
How does adding a catalyst affect K
Still, doesn’t affect the K.
Adding a catalyst only increases the rate of the reaction, but it doesn’t affect the position of the EC.
