Unit 2- Physical chemistry

Question 1

When is a chemical reaction in equilibrium?

Answer 1

When the composition of the reactants and products remains constant indefinitely

Question 2

What value is given to the concentrations of pure solids and pure liquids at equilibrium?

Answer 2

They are taken as constant and given a value of 1

Question 3

What does the numerical value of the equilibrium constant depend on, and what is it not affected by?

Answer 3

Depends on temperature

Not affected by concentration and/or pressure

Question 4

What is a endothermic reaction?

Answer 4

Reactions that take in energy from their surroundings, the enthalpy change is positive

Question 5

What is a exothermic reaction?

Answer 5

Reactions that transfer energy to their surroundings, the enthalpy change is negative

Question 6

For an endothermic reaction what affect does an increase in temperature have an the K value and the yield of product?

Answer 6

The K value increases and the product yield increases

Question 7

For an exothermic reaction what affect does an increase in temperature have an the K value and the yield of product?

Answer 7

The K value decreases and the product yield decreases

Question 8

Does the presence of a catalyst affect the value of the equilibrium constant?

Answer 8

No

Question 9

Water is said to be amphoteric, what is meant by this term?

Answer 9

It can react as an acid and a base

Question 10

What is the dissociation constant for the ionisation of water known as?

Answer 10

The ionic product

Question 11

What are the Bronsted-Lowry definitions of acids and bases?

Answer 11

An acid in a proton donor and a base is a proton acceptor

Question 12

What can be said about acids and bases in a reaction?

Answer 12

For every acid there is a conjugate base, formed by the loss of a proton and for every base there is a conjugate base formed by the gain of a proton

Question 13

What happens to strong acids and strong bases in aqueous solution?

Answer 13

They dissociate completely into ions

Question 14

What happens to weak acids and weak bases in aqueous solution?

Answer 14

They only partially dissociate into ions

Question 15

What are 3 examples of strong acids?

Answer 15

• hydrochloric acid (HCl)
• sulfuric acid (H2SO4)
• nitric acid (HNO3)

Question 16

What are 3 examples of weak acids?

Answer 16

• ethanoic acid
• carbonic acid
• sulfurous acid

Question 17

What are an example of a strong base?

Answer 17

Solutions of metal hydroxides e.g. aluminium hydroxide

Question 18

What are 2 examples of weak bases?

Answer 18

• ammonia

- amines

Question 19

What do a soluble salt of a strong acid and a strong base produce when dissolved in water?

Answer 19

A neutral solution

Question 20

What do a soluble salt of a weak acid and a strong base produce when dissolved in water?

Answer 20

An alkaline solution

Question 21

What do a soluble salt of a strong acid and a weak base produce when dissolved in water?

Answer 21

An acidic solution

Question 22

What is a buffer solution?

Answer 22

One in which the pH remains approximately constant when small amounts of acid, base or water are added

Question 23

What does an acid buffer consist of?

Answer 23

A solution of a weak acid and one of its salts made from a strong base

Question 24

What does a basic buffer consist of?

Answer 24

A solution of a weak base and one of its salts

Question 25

What are indicators?

Answer 25

Weak acids

Question 26

In aqueous solution what should the colour of an acid indicator be distinctly different from?

Answer 26

The colour of its conjugate base

Question 27

How can suitable indicators be selected?

Answer 27

From pH data, including titration curves

Question 28

What is the standard enthalpy of formation?

Answer 28

The enthalpy change when one mole of a substance is formed from its elements in their standard states

Question 29

What is the standard state of a substance?

Answer 29

Its most stable state at a pressure of 1 atmosphere and at a specified temperature, usually taken as 298 K

Question 30

What is the entropy of a system a measure of?

Answer 30

The degree of disorder of the system

Question 31

What is the relationship between the degree of disorder and entropy?

Answer 31

The greater the degree of disorder, the greater the entropy

Question 32

What can be said about the disorder of solids and gases?

Answer 32

Solids have low disorder and gasses have high disorder

Question 33

What happens to entropy when temperature increases?

Answer 33

Entropy increases

Question 34

At what points is their a rapid increase in the entropy of a substance?

Answer 34

There is a rapid increase in entropy at a the melting point of a substance and then an even more rapid and larger change in entropy at the boiling point

Question 35

What does the second law of thermodynamics state?

Answer 35

The total entropy of a reaction system and its surroundings always increases for a spontaneous process

Question 36

What does heat energy released by the reaction system lead to?

Answer 36

An increase in the entropy of the surroundings

Question 37

What does heat energy absorbed by the reaction system lead to?

Answer 37

A decrease in the entropy of the surroundings

Question 38

What does the third law of thermodynamics state?

Answer 38

The entropy of a perfect crystal at 0 K is zero

Question 39

What is the standard entropy of a substance?

Answer 39

The entropy value for the substance in its standard state

Question 40

If the change in free energy between reactants and products is negative what can be said?

Answer 40

A reaction may occur and the reaction is said to be feasible

Question 41

What is a feasible reaction?

Answer 41

One which tends towards the products rather than the reactants

Question 42

At equilibrium what is the value of free energy?

Answer 42

zero

Question 43

What does the rate of a chemical reaction depend on?

Answer 43

The concentrations of the reactants

Question 44

What is the overall order of a reaction?

Answer 44

The sum of the powers to which the concentrations of the reactants are raised in the rate equation

Question 45

What is the rate of reaction dependent on?

Answer 45

The slowest step, which is called the "rate determining step"

Question 46

What does the equilibrium constant (K) characterise?

Answer 46

The equilibrium composition of the reaction mixture

Question 47

What does the value of the equilibrium constant (K) indicate?

Answer 47

The position of equilibrium

Question 48

What units do equilibrium constants have?

Answer 48

None, they don’t have units

Question 49

What value are the concentrations of pure liquids and pure solids at equilibrium given in the equilibrium equation?

Answer 49

They are taken as a constant and given a value of 1

Question 50

What does the ionic product vary with?

Answer 50

Temperature

Question 51

What is H3O+ ?

Answer 51

A hydronium ion (a hydrated proton). A shorthand representation is H+

Question 52

What is the ionic product of water (approximately) at 25*c?

Answer 52

1 x 10 ^-14 (in databook)

Question 53

What is enthalpy?

Answer 53

The energy stored in chemical bonds

Question 54

How can the order of reaction be determined?

Answer 54

Only from experimental data