Equillibrium II- Topic 11

Question 1

How to calculate kc

Answer 1

Kc =
[ C]^p [D]^q / [ A]^m [B]^n

p, q, m and n represent the big numbers infront of the chemicals in the chemical equation

Question 2

How to calculate moles at equilibrium

Answer 2

moles of reactant at equilibrium = initial moles – moles reacted
moles of product at equilibrium = initial moles + moles formed

Question 3

Practical to work out kc value of ethanol and ethanoic acid (it’s an esterification reaction)

Answer 3

Part 1 Preparing the equilibrium mixture
1 Use burettes to prepare a mixture in boiling tube of carboxylic acid, alcohol, and dilute sulfuric acid.
2 Swirl and bung tube. Leave the mixture to reach equilibrium for one week

Part 2 Titrating the equilibrium mixture
1 Rinse a 250 cm volumetric flask with distilled water.
Use a funnel to transfer the contents of the boiling tube into the flask. Rinse the boiling tube with water and add the washings to the volumetric flask.
2 Use distilled water to make up the solution in the volumetric flask to exactly 250 cm.
Stopper the flask, then invert and shake the contents thoroughly.
3 Use the pipette to transfer 25.0 cm? of the diluted equilibrium mixture to a 250 cm’ conical flask.
4 Add 3 or 4 drops of phenolphthalein indicator to the conical flask.
5 Set up the burette with sodium hydroxide solution..
6 Add the sodium hydroxide solution from the burette until the mixture in the conical flask just turns pink.
Record this burette reading in your table.
7 Repeat the titration until you obtain a minimum of two concordant titres.

Question 4

What is the partial pressure of a gas

Answer 4

The partial pressure of a gas in a mixture is the pressure that the gas would have if it alone occupied the volume occupied by the whole mixture.

Question 5

How to work out the partial pressure of a gas

Answer 5

partial pressure = mole fraction x total pressure

Question 6

How to work out the mole fraction

Answer 6

Number of moles of a gas/ total number of moles of a gas

Question 7

Expression for kp

Answer 7

The same as kc but with pressure instead of concentration

Question 8

What is the only thing that can change the value of kp or kc

Answer 8

Temperature

Question 9

How can kc be used to predict the extent a reaction might occur

Answer 9

If kc < 10^-10 then the reaction will stop
If kc = 0.1 then the reactants predominate in equilibrium
If kc = 1 there is an equal amount of reactants and products
If kc = 10 then the products predominate in equilibrium
If kc > 10^10 then the reaction goes to completion