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AH Chemistry (short) > Unit 2- Physical chemistry > Flashcards

Unit 2- Physical chemistry Flashcards

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1
Q

When is a chemical reaction in equilibrium?

A

When the composition of the reactants and products remains constant indefinitely

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2
Q

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

A

They are taken as constant and given a value of 1

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3
Q

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

A

Depends on temperature

Not affected by concentration and/or pressure

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4
Q

What is a endothermic reaction?

A

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

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5
Q

What is a exothermic reaction?

A

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

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6
Q

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

A

The K value increases and the product yield increases

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7
Q

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

A

The K value decreases and the product yield decreases

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8
Q

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

A

No

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9
Q

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

A

It can react as an acid and a base

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10
Q

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

A

The ionic product

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11
Q

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

A

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

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12
Q

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

A

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

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13
Q

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

A

They dissociate completely into ions

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14
Q

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

A

They only partially dissociate into ions

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15
Q

What are 3 examples of strong acids?

A
  • hydrochloric acid (HCl)
  • sulfuric acid (H2SO4)
  • nitric acid (HNO3)
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16
Q

What are 3 examples of weak acids?

A
  • ethanoic acid
  • carbonic acid
  • sulfurous acid
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17
Q

What are an example of a strong base?

A

Solutions of metal hydroxides e.g. aluminium hydroxide

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18
Q

What are 2 examples of weak bases?

A
  • ammonia

- amines

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19
Q

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

A

A neutral solution

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20
Q

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

A

An alkaline solution

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21
Q

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

A

An acidic solution

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22
Q

What is a buffer solution?

A

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

23
Q

What does an acid buffer consist of?

A

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

24
Q

What does a basic buffer consist of?

A

A solution of a weak base and one of its salts

25
Q

What are indicators?

A

Weak acids

26
Q

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

A

The colour of its conjugate base

27
Q

How can suitable indicators be selected?

A

From pH data, including titration curves

28
Q

What is the standard enthalpy of formation?

A

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

29
Q

What is the standard state of a substance?

A

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

30
Q

What is the entropy of a system a measure of?

A

The degree of disorder of the system

31
Q

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

A

The greater the degree of disorder, the greater the entropy

32
Q

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

A

Solids have low disorder and gasses have high disorder

33
Q

What happens to entropy when temperature increases?

A

Entropy increases

34
Q

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

A

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

35
Q

What does the second law of thermodynamics state?

A

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

36
Q

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

A

An increase in the entropy of the surroundings

37
Q

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

A

A decrease in the entropy of the surroundings

38
Q

What does the third law of thermodynamics state?

A

The entropy of a perfect crystal at 0 K is zero

39
Q

What is the standard entropy of a substance?

A

The entropy value for the substance in its standard state

40
Q

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

A

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

41
Q

What is a feasible reaction?

A

One which tends towards the products rather than the reactants

42
Q

At equilibrium what is the value of free energy?

A

zero

43
Q

What does the rate of a chemical reaction depend on?

A

The concentrations of the reactants

44
Q

What is the overall order of a reaction?

A

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

45
Q

What is the rate of reaction dependent on?

A

The slowest step, which is called the “rate determining step”

46
Q

What does the equilibrium constant (K) characterise?

A

The equilibrium composition of the reaction mixture

47
Q

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

A

The position of equilibrium

48
Q

What units do equilibrium constants have?

A

None, they don’t have units

49
Q

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

A

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

50
Q

What does the ionic product vary with?

A

Temperature

51
Q

What is H3O+ ?

A

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

52
Q

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

A

1 x 10 ^-14 (in databook)

53
Q

What is enthalpy?

A

The energy stored in chemical bonds

54
Q

How can the order of reaction be determined?

A

Only from experimental data

AH Chemistry (short) (4 decks)

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