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Chemistry > Topics 10 & 11 Equilibrium Notes > Flashcards

Topics 10 & 11 Equilibrium Notes Flashcards

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1
Q

Dynamic equilibrium

A

A reversible reaction that proceeds at the same rate in both directions with constant concentrations of the reactants and products in a closed system.

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2
Q

Open system

A

One or more of the reactants/products can escape.

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3
Q

When pressure is increased, equilibrium: position shifts…

A

To the side with the fewest gas moles. Pressure changes only affect the equilibrium, if there is a gaseous substance involved.

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4
Q

What factors affect the position of equilibrium?

A

Temperature, pressure and concentration.

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5
Q

Where are all 4 components, if the reaction is in equilibrium?

A

Present.

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6
Q

What happens to a system in dynamic equilibrium when products are removed?

A

The reaction goes to completion.

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7
Q

Haber process equation

A

N2 + 3H2 —> 2NH3. Everything in the gaseous state. Exothermic.

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8
Q

Conditions of the Haber process

A

450 degrees Celsius, 250 atm and an iron catalyst.

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9
Q

What happens when temperature is increased, if the forwards reaction is Exothermic?

A

The equilibrium position shifts left.

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10
Q

The contact process

A

A step in producing sulphuric acid using a Vanadium oxide catalyst. 2SO2 + O2 <—> 2SO3. Everything in the gaseous state.

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11
Q

What is special about sulphuric acid?

A

It is diprotic.

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12
Q

Where does the hydrogen for the Haber process come from?

A

Methane (& sometimes electrolysis of water).

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13
Q

For the Haber process, what do the equilibrium and kinetic theories favour?

A

Equilibrium theory: low temperature & higher pressure.
Kinetic theory: a catalyst, high pressure and high temperature.

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14
Q

What issues does higher pressure create?

A

Unsafe/explosion risk. Higher energy and materials costs (as a thicker-walled reaction vessel must be constructed).

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15
Q

Average yield if the Haber process

A

15%.

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16
Q

The Haber process: step by step

A

A pump compresses the gas. The reaction vessel has a high surface area. Gasses are passed through a condenser. Ammonia condenses first, liquid ammonia is removed and the equilibrium position shifts right.

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17
Q

Feedstock recycling

A

A pump is used in the Haber process to circulate unreacted N2 and H2 (both gaseous).

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18
Q

What is 80% of the ammonia produced by the Haber process used for?

A

Fertilisers, such ammonium nitrate (NITRAM) and ammonium sulphate. NH3 + HNO3 —> NH4NO3. 2NH3 + H2SO4 —> (NH4)2SO4. Ammonia can be oxidised to nitric acid to make fertilisers, explosives (TNT) and polyamide polymers (nylon).

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19
Q

Compromise conditions

A

Reaction conditions which produce the require product most cost-effectively and safely. Consider the rate and the yield.

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20
Q

Le Chatelier’s principle

A

When a change in conditions is applied to a system in equilibrium, the equilibrium position shifts to counteract this change/ the system reacts to oppose this change.

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21
Q

In the Haber process, how is ammonia removed from the mixture of gases issuing from the converter?

A

Cooling and compression, so ammonia can be removed as a liquid.

22
Q

Why might a product be removed before it’s maximum concentration is achieved?

A

Unreacted reactants can be recycled. It may take too long to reach equilibrium. To ensure the equilibrium position is shifted to favour the products.

23
Q

K

A

Equilibrium constant.

24
Q

When does K= Kc?

A

If the reactant & product concentrations spare expressed in moldm-3. For (g) and (aq).

25
Q

When does K=Kp?

A

If the reactant & product concentrations are expressed in partial pressure (ppm). Only for (g).

26
Q

Ka

A

Acids.

27
Q

What does the expression of K depend upon?

A

Only the stoichiometry. Not the mechanism.

28
Q

What are the stoichiometric numbers used for in the expression of Kc?

A

Powers.

29
Q

Expression for Kc— format

A

(Product concentrations raised to the power of their respective stoichiometric numbers & multiplied by one another) divided by (the reactant concentrations raised to their respective powers & multiplied by one another). Products on the top. All concentrations AT EQUILIBRIUM.

30
Q

Homogeneous equilibrium

A

All substances participating in the reversible reaction are in the same phase (gaseous or aqueous).

31
Q

Heterogeneous equilibrium

A

When reactants and products are in two or more states.

32
Q

Why are the concentrations of pure solids & pure liquids omitted from the equilibrium expression?

A

They are constant, so do not influence the equilibrium.

33
Q

If the only product(s) is(are) solid or liquid, what does the equilibrium expression look like?

A

A 1 atop the reactants. Vice versa for when the reactants are solid/liquid.

34
Q

What does the value of Kc estimate?

A

How complete the reaction is at a particular temperature.

35
Q

What is the extent of the reaction, if Kc > 10 to the power of 10?

A

The reaction is almost complete.

36
Q

What is the extent of the reaction, if the value of Kc is in the range 10 to the power of 4 to 10 to the power of 10?

A

The reaction favours the products.

37
Q

What is the extent of the reaction, if the value of of Kc is in the range 10 to the power of -4 to 10 to the power of 4?

A

Reactants and product form in similar amounts.

38
Q

What is the extent of the reaction, if the value of Kc ranges from 10 to the -10 to 10 to the -4?

A

The reaction favours the reactants.

39
Q

What is the extent of the reaction, if the value of Kc < 10 to the power of -10?

A

The reaction is not noticeable.

40
Q

When are the products favoured?

A

When Kc > 10 to the power of 3.

41
Q

When does the reaction favour the reactants?

A

When Kc is less than 10 to the power of -3.

42
Q

What is the only factor which affects Kc?

A

NOT pressure. NOT volume. NOT concentration. ONLY TEMPERATURE.

43
Q

What if Kc = 1?

A

There are equal concentrations of reactants and products.

44
Q

When Kc ranges from 10 to the -3 to 10 to the 3?

A

Reactants roughly equal products in concentration.

45
Q

How do you find the units of Kc?

A

Sub in mol dm-3 wherever there is a concentration. Remember to consider the powers. Cancel appropriately.

46
Q

When the reactants and products of the reaction are flipped?

A

Kc is the reciprocal. Kc’ = 1/Kc.

47
Q

1 / (mol dm-3)

A

= Mol -1 dm3.

48
Q

Other features of Kc

A

It can have no units. It is always positive.

49
Q

When answering a question of equilibrium…

A

Always write out the Kc expression.

50
Q

CS2 (g) + 3Cl2 (g) <—> S2Cl2 (g) + CCl4 (g). Calculate the value of the equilibrium constant Kc when the initial concentrations of the reactants are 1.2 mol dm-3 and 3.6 mol dm-3 respectively. The concentration of CCl4 at equilibrium is 0.9 mol dm-3.

A

Create a table. Use the ice method. The change for the products is +; for the reactants it’s -. Unless otherwise stated, concentration of products initially is 0. Use the stoichiometric ratio where calculating the change in concentration from initial to equilibrium of each component. Sub into the Kc expression. Find the units. Algebra may be required (e.g., represent the change as x) for similar questions. Ensure your concentrations are given in mol dm-3, not as moles unless the volumes can be cancelled. Answer: 3.7 mol-2 dm6.

Chemistry (23 decks)

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