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Chemistry AS Level - Sabrina Belfi Chapters 8 And 9 > Chapter 8 - Equilibrium > Flashcards

Chapter 8 - Equilibrium Flashcards

Definition, formulae and key ideas

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1
Q

Definition of reversible reaction

A

A reaction in which the products can be changed back to reactants by reversing the conditions.

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2
Q

Definition of an equilibrium reaction

A

A reaction that does NOT go to completion and in which reactants and products are present in fixed concentration ratios.

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3
Q

Definition of dynamic equilibrium

A

In an equilibrium mixture, molecules of reactants are being converted to products at the same rate as products are being converted to reactants.

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4
Q

Definition of a closed system

A

A system in which matter or energy is not lost or gained. , e.g. Gases in a closed vessel

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5
Q

Definition of an open system

A

A system in which matter is lost or gained , e.g. A mixture of solids and gases in an open beaker

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6
Q

Definition of Le Chatelier’s principle

A

When any of the conditions (concentration, pressure , temperature) affecting the position of the equilibrium are changed, the position of that equilibrium shifts to minimise (oppose ) the change .

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7
Q

Definition of the equilibrium constant , Kc

A

A constant calculated from the equilibrium expression for a reaction

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8
Q

Definition of the equilibrium expression :

A

A simple relationship that links Kc to the equilibrium concentrations of reactants and products and the stoichiometric equation.

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9
Q

Definition of partial pressure

A

The pressure that an individual gas contributes to the overall pressure in a mixture of gases.

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10
Q

Definition of an acid

A

A proton (hydrogen ion) donor.

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11
Q

Definition of a base

A

A proton (hydrogen ion ) acceptor.

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12
Q

Definition of an alkali

A

A base that is soluble in water.

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13
Q

Definition of amphoteric plus an example

A

Able to behave as both an acid and a base. Aluminium oxide, Al2O3 is amphoteric.

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14
Q

Definition of Brønsted- Lowry theory of acids

A

Acids are proton donors and bases are proton acceptors.

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15
Q

Definition of conjugate pair (acid/base)

A

An acid and a base on each side of an equilibrium equation that are related to each other by the difference of a proton . E.g. the acid in the forward reaction and the base in the reverse reaction or the base in the forward reaction and the acid in the reverse reaction..

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16
Q

Definition of dissociation

A

The break up of a molecule into ions, for example, when HCl molecules dissolve in aqueous solution, they dissociate completely into H^+ and Cl^- ions.

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17
Q

Definition of a strong acid

A

Acids that dissociate almost completely in solution.

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18
Q

Definition of a weak acid

A

An acid that only partially dissociates in solution

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19
Q

Definition of a weak base

A

Bases that only dissociate to a small extent in solution

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20
Q

Definition of a strong base

A

Bases that dissociate almost completely in solution.

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21
Q

Dissociate is the same as….

A

Ionise (same meaning in this chapter )

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22
Q

An example of a reversible reaction:

CuSO4. 5H2O (s)                 ↔             CuSO4 (s)              + 5H2O  (l)
Hydrated copper(II) sulfate        anhydrous copper (II) sulfate

What is the colour of hydrated and anhydrous copper (II) sulfate?

A

Hydrated = blue

Anhydrous = white

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23
Q

What are the 4 characteristics of equilibrium?

A
  1. It’s dynamic
  2. The forward and reverse reactions occur at the same rate.
  3. The concentrations of reactants and products remain constant at equilibrium
  4. It requires a closed system
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24
Q

Equilibrium characteristic:

  1. It’s dynamic, dynamic equilibrium means …
A

That the molecules or ions are continously reacting. Reactants are continuously being changed to products and products are continuously being changed back to reactants.

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25
Q

Characteristic of equilibrium

  1. The forward and backwards reactions occur at the same rate ….refers to…
A

At equilibrium the rate of the forward reaction = the rate of the backwards reaction.

Molecules or ions of reactants are becoming products, and those in the products are becoming reactants , at the same rate.

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26
Q

What colour gas is iodine ?

A

Purple

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27
Q

Characteristic of equilibrium

  1. Requires a closed system
A

Otherwise reactants/ products escape the reaction mixture and the reaction can no longer be reversible because there is not enough product /reactants for an example.

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28
Q

The position of the equilibrium refers to …

A

The relative amounts of products and reactants present in an equilibrium mixture.

29
Q

If a system in equilibrium is disturbed it can shift to the right or left, explain these shifts :

A

○ Right shift: the concentration of the products is increases relative to the reactants

○ left shift : the concentration of the products is decreased relative to the reactants

30
Q

State Le Chatelier’s principle

A

If one or more factors that affect an equilibrium is change, the position of the equilibrium shifts in the direction that reduces (opposes) the change.

31
Q

What are the 3 factors that affect equilibrium?

A
  1. Temperature
  2. Concentration
  3. Pressure ( only affects reaction mixtures with gases)
32
Q

We can predict the effect of changing the concentration and/or pressure by referring to….

A

the stoichiometric equation for the reaction

33
Q

We can predict the effect of changing temperature by referring to…..

A

The enthalpy of the reaction, whether it is exothermic or endothermic.

34
Q

How does change in concentration affect the position of equilibrium?
3 points for each

  1. When the concentration of one or more of the reactants is increased
  2. When the concentration of one or more of the products is increased
A
  1. Concentration of reactants increase :
  • the system is no longer in equilibrium
  • the position of equilibrium moves to the right to reduce the effect
  • More products are formed until equilibrium is restored
  1. When the concentration of one or more of the products is increased;:

• the system is no longer in equilibrium

35
Q

What causes pressure of a gas?

A

Molecules hitting the walls on the container

36
Q

At a constant temperature, the more gas molecules there are in a given volume, the higher the…….
And why

A

Pressure because in a mixture of gases each molecule contributes toward the total pressure.

37
Q

.Use : X (g) + Y (g) ➡ Z (g)
1 mol 1mol 1mol

2 moles on left and 1 mole on right so the equilibrium shifts in the direction of ….

A

Fewer gas molecules (in the direction that opposes the increase in pressure).

38
Q

When pressure is decreased equilibrium shifts in…

A

The direction that increases the number of molecules of gas.

Example:

2SO2 (g) + O2 (g) ↔2 SO3 (g)

It would shift to the left.

39
Q

What are 2 important things to note about equilibrium and pressure ?

Hints :

  1. If there are equal numbers of gas molecules on both sides…
  2. In a reaction involving gases and solids (or liquids), it is only the …
A
  1. Changes in pressure then have no affect on equilibrium

2. Molecules of gas that determine how pressure affects the position of equilibrium

40
Q

If the forward reaction is exothermic, an increase in temperature would favour ….

A

The backwards reaction (the endothermic )

41
Q

Endothermic reactions are favoured by an increase/decrease in temperature ?

A

Increase in temperature

42
Q

Exothermic reactions are favoured by a increase/decrease in temperature ?

A

Decrease in temperature

43
Q

Do catalyst have any affect on the position of equilibrium and why ?

A

No because they increase the rate of both the forward and reverse reactions equally.

44
Q

Equilibrium expressions and the equilibrium constant, Kc

How would you write it for the general equation :

mA + nB ↔ pC + qD

Where m,n, p, q are number of moles in the equation

A

[C]^p [D]^q
Kc = ⚊⚊⚊⚊⚊
[A]^m [B]^n

Details : - In the square brackets are the concentrations of reactants and products

           - To the power of the number of moles of each 
           - products over reactants 
           - units within the brackets are concentrations and therefore their units are moldm^-3. The units of Kc depend on the equilibrium expression.
45
Q

Kc, and concentration changes :

If the concentration of products or reactants is altered and all the other conditions remain constant ,does the value of Kc change?

A

No

46
Q

Kc and pressure changes :

If all the other conditions remain constant does an altering in pressure affect the value of Kc ?

A

No

47
Q

Kc and temperature changes :

If all conditions are kept the same , and temperature is increased , what happens to Kc for ..

  1. A exothermic reaction
  2. Endothermic

Hint : Think of how equilibrium shifts

A
  1. Exothermic : with an increase in temperature, Kc decreases (opposite)
  2. Endothermic : with increasing temperature, Kc increases (together)
48
Q

The pressure exerted by any one gas in the mixture is called its. ..

A

Partial pressure

49
Q

Equilibrium expressions involving partial pressures :

Use

N2 (g) + 3H2 (g) ↔ 2NH3 (g)

To deduce an expression for Kp

A

P^2 NH3
Kp = ⚊⚊⚊⚊⚊
P N × P^3 H2

Details : - products over reactants
- p is the number are moles of that particular reactant or product

50
Q

A high Kc value means …

A

Products are favoured , think of formula

51
Q

A low Kc means ….

A

Reactants were favoured

52
Q

Formula for partial pressure

A

Partial pressure = mole fraction × total pressure

Mole fraction = number of moles of particular gas / total number of moles in vessel

53
Q

What does ice stand for and what is the table used for

A

I-initial

C- change

E- Equilibrium

Details :
•You put the balanced equation on the top

  • at initial the products are usually zero
  • it is for concentration or number of moles
54
Q

What are the units of Kp ?

A

The units of pressure are pascals, Pa . The units of Kp depend on the form of the equilibrium expression

55
Q

Very high pressure is not used , why?

A

It’s expensive to create reaction vessels that can withstand those high pressures

56
Q

What are two very important equilibria in the chemical industry?

A
  1. Ammonia production (the Haber process)

N2 (g) + 3H2 (g) ↔ 2NH3 (g) forward reaction is exothermic

  1. Sulfuric acid production (the contact process )

2SO2 (g) + O2 (g) ↔ 2SO3 (g) forward reaction is exothermic

57
Q

What is the formula for nitric acid ?

A

HNO3

58
Q

What is the formula for sulfuric acid ?

A

H2SO4

59
Q

Formula for ethanoic acid

A

CH3COOH

60
Q

Formula for benzoic acid

A

C6H5COOH

61
Q

When acids ionise in water what is always one of the ions present?

A

H+

62
Q

The five important bases:

  1. Calcium Oxide
  2. Copper (II) oxide
  3. Sodium hydroxide
  4. Calcium hydroxide
  5. Ammonia

What are they formula ?

A
  1. CaO
  2. CuO

3 . NaOH

  1. Ca (OH)2
  2. NH3
63
Q

Is water an acid or/and a base?

A

Both, it’s amphoteric

64
Q

A Brønsted Lowry acid is….

A

A proton donor

65
Q

A Brønsted Lowry base is a…

A

Proton acceptor

66
Q

Use water (amphoteric ) to show how acid and bases behave

  1. HCl + H2O
  2. NH3 + H2O

What are the products?

A
  1. HCl (acid )(g) + H2O (base ) (l)➡ H3O^+ (aq) + Cl-(aq)
  2. NH3 (base )(g) + H2O (acid ) (l)↔ NH4^+(aq) + OH^- (aq)
67
Q

An example of a strong and weak acid

A

Strong= HCl

Weak = ethanoic acid

68
Q

An example of a strong and weak base

A

Strong= sodium hydroxide

Weak = ammonia

69
Q

Strong and weak acids and bases can be distinguished by their pH values of their aqueous solutions :

What pH would a strong acid or base have ?

A

Strong acid = 0

Strong base = 14

Chemistry AS Level - Sabrina Belfi Chapters 8 And 9 (2 decks)

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