Reactivity 2.3 (SL)

Question 1

Dynamic equilibrium

Answer 1

When a rxn reaches equilibrium the rxn doesn’t stop, but the rate of the forward rxn is equal to the rate of the reverse rxn, so the equilibrium concs of the reactants and products remains constant.

Question 2

When the value of K is large (>100)…

Answer 2

The reaction has virtually gone to completion and the concn of reactants in the equilibrium mixture is very small

Question 3

When the value K is small (<0.01)…

Answer 3

The reaction has hardly proceeded and the concn of the the products in the equilibrium mixture is very small

Question 4

If the value of K is in the range of 1 (between 10^-2 and 10^2)…

Answer 4

There will be appreciable amounts of both products and reactants in the equilibrium mixture

Question 5

Equilibrium constant symbol and units

Answer 5

Symbol: K
Units: No units

Question 6

What is the equilibrium constant for the reverse rxn

Answer 6

The reciprocal of the constant for the forward direction

Question 7

How do the rates of the forward and backward reactions compare at equilibrium?

Answer 7

They are equal

Question 8

Dynamic equilibrium

Answer 8

The rxn has not stopped, but both forward and backward reactions are occurring at the same rate

Question 9

Equilibrium can be reached from either direction

Answer 9

This is because the same equilibrium rxn will result under the same conditions. No matter whether the rxn is started with all reactants, all products or a mixture

Question 10

Effect on macroscopic (observable) properties at equilibrium

Answer 10

No effect, they stay the same as they depend on concs and components of the mixture (which are staying the same)

Question 11

The concentrations of reactant and product are ____ but not ____ at equilibrium

Answer 11

constant, equal

Question 12

Equilibrium position

Answer 12

The proportion of reactant and product in the equilibrium mixture.

Question 13

The equilibrium position of reactions thats mixtures contain predominantly products are said to…

Answer 13

Lie to the right

Question 14

The equilibrium position of reactions thats mixtures contain predominantly reactants are said to…

Answer 14

Lie to the left

Question 15

What are the factors that effect the position of equilibrium?

Answer 15

• Concentration
• Pressure
• Temp
• not the addition of a catalyst

Question 16

Le Chatelier’s Principle

Answer 16

A system at equilibrium when subjected to a change will respond in such a way as to minimize the effect of the change. (Whatever you do the system at equilibrium, the system will respond in the opposite way)

Question 17

Why does the addition of a catalyst not affect the position of equilibrium?

Answer 17

The catalyst affects both the forward and reverse rxns equally. The catalyst will help the system to reach equilibrium faster though.

Question 18

What conc changes would cause an eq shift to the left?

Answer 18

Inc in conc of product or dec in conc of reactant

Question 19

How would you manipulate K when reversing the rxn?

Answer 19

take its reciprocal

Question 20

How would you manipulate K when adding two rxns together?

Answer 20

Multiply the K value of each rxn together

Question 21

How would you manipulate K when doubling all the coefficients in a rxn?

Answer 21

Square K

Question 22

How would you manipulate K when halving all the coefficients in a rxn?

Answer 22

Square root K

Question 23

How do industrial facilities increase the yield of product?

Answer 23

By removing product as it forms, forcing equilibrium to be continuously pulled to the right

Question 24

When there is no overall volume change during a reaction and pressure is inc/dec what is the effect on the equilibrium position?

Answer 24

It will have no effect on the equilibrium position as the products and reactants will be affected equally.

Question 25

When the volume decreases during a reaction and pressure is inc/dec what is the effect on the equilibrium position?

Answer 25

The equilibrium position is shifted towards the product side (the side with less volume) to minimise the increased pressure.

Question 26

What type of rxn is heat a product in?

Answer 26

Exothermic

Question 27

How to move equilibrium position to the product side of an exothermic rxn?

Answer 27

Removing heat (product) by lowering the temp

Question 28

How to move equilibrium position to the product side of an endothermic rxn?

Answer 28

Increasing temp

Question 29

For exothermic rxns the higher the temp the ___ the value of K

Answer 29

lower

Question 30

For endothermic rxns the higher the temp the ___ the value of K

Answer 30

greater

Question 31

Effect of Concentration on equilibrium position and change in value of K

Answer 31

Equilibrium position: changes
Change in K: no change

Question 32

Effect of pressure on equilibrium position and change in value of K

Answer 32

Equilibrium position: changes if rxn involves a change in no. of gas molecules
Change in K: no change

Question 33

Effect of temp on equilibrium position and change in value of K

Answer 33

Equilibrium position: changes
Change in K: changes

Question 34

Effect of catalyst on equilibrium position and change in value of K

Answer 34

Equilibrium position: no change
Change in K: no change

Question 35

When do Heterogenous Equilibria occur?

Answer 35

When one or more products or reactants is in a different pase to the other reactants and products.

Question 36

Why do solids not appear in equilibria expressions?

Answer 36

Because they don’t have a concentration