Unit 2 - Physical Chemistry

Question 0

At dynamic equilibrium, what can be said about the concentrations of the reactants and products?

Answer 0

They are constant but not equal.

Question 1

Define dynamic equilibrium.

Answer 1

A chemical reaction is in dynamic equilibrium when the rate of the forward reaction is equal to the rate of the reverse reaction.

Question 2

State three factors that can affect the position of equilibrium.

Answer 2

• altering the concentration of a reactant or product species
• changing the pressure if there are different numbers of moles of gases on both sides of the balanced equation
• altering the temperature

Question 3

What effects does a catalyst have on the position of equilibrium?

Answer 3

None whatsoever. It only speeds up the rate at which equilibrium is reached.

Question 4

The equilibrium constant is given by what symbol?

Answer 4

K

Question 5

What units does the equilibrium constant have?

Answer 5

The equilibrium constant has no units.

Question 6

Define homogeneous equilibrium.

Answer 6

All of the species are in the same phase.

Question 7

Define heterogenous equilibrium.

Answer 7

The species present are in more than one phase.

Question 8

Pure solids and pure liquids are given what value in an equilibrium equation?

Answer 8

1

Question 9

What parameters have no effect on the value of equilibrium constant?

Answer 9

Changes in concentration, pressure and the presence of a catalyst.

Question 10

Is an equilibrium constant independent or dependant of temperature?

Answer 10

It is temperature dependent.

Question 11

Describe the effect of increasing temperature on the value of the equilibrium constant provided the reaction is endothermic.

Answer 11

For an endothermic reaction, and increase in temperature favours the production of the products and so the ratio of products to reactants increases, thus the value of K increases.

Question 12

Describe the effect of increasing temperature on the value of the equilibrium constant provided the reaction is exothermic.

Answer 12

For an exothermic reaction, and increase in temperature favours the reactants and so the ratio of products to reactants will decrease, thus the value of K will also decrease.

Question 13

What is Le Chateliér’s principle?

Answer 13

This is the principle that describes the process by which a reaction at equilibrium is subjected to a stress and the composition alters in such a way so as to minimise the effects of that stress.

Question 14

What is the formula for the Rf value of a substance during paper chromatography?

Answer 14

Rf = Distance travelled by solute/Distance travelled by solvent

Question 15

What is a partition coefficient?

Answer 15

A partition coefficient, is the value of the equilibrium constant which involves the concentration of a particular solute, distributed between two species (layers).

Question 16

What parameters affect the value of the partition coefficient?

Answer 16

Temperature and the identies of the solute and solvent.

Question 17

What is the Bronsted-Lowry definition of an acid?

Answer 17

Acids are proton donors.

Question 18

What is the Bronsted-Lowry definition of a base?

Answer 18

A base is a proton acceptor.