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

A + B –> C + D

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 pipettes to prepare a mixture in a boiling tube of carboxylic acid, alcohol, and dilute sulfuric acid.
2) Swirl and bung the 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.
2) 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.
3) 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.
4) Use the pipette to transfer 25.0 cm3 of the diluted equilibrium mixture to a 250 cm3 conical flask.
5) Add 3 or 4 drops of phenolphthalein indicator to the conical flask.
6) Set up the burette sodium hydroxide solution
7) Add the sodium hydroxide from the burette until the mixture in the conical flask just turns pink.
8) Record this burette reading in your table
9) Repeat the titration until you obtain a minimum of two concordant titres.

Question 4

What is the partial pressure of a gas

Answer 4

Partial pressure is the pressure exerted by a single gas in a mixture of gases. It is the pressure that the gas would exert if it occupied the entire volume of the container by itself, at the same temperature.

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