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A Level Chemistry (OCR) Module 3 > 10.4 Dynamic Equilibrium and le Chatlier's principle > Flashcards

10.4 Dynamic Equilibrium and le Chatlier's principle Flashcards

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1
Q

When ignited, what does hydrogen react with oxygen to form

A

Water

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2
Q

What is a reversible reaction

A

Reactions that take place in both ‘forward’ and ‘reverse’ directions.

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3
Q

What type of reaction is the Haber process

A

A reversible reaction

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4
Q

What is a product of the Haber process

A

Ammonia

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5
Q

Equation of the Haber process

A

N2(g) + 3H2(g) 2NH3(g)

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6
Q

In an equilibrium system:

A

The rate of the forward reaction is equal to the rate of the reverse reaction
The concentrations of reactants and products do not change

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7
Q

Equilibrium systems are ______. At equilibrium, both the forward and reverse reactions are taking place. As fast as the reactants are becoming products, the products are reacting to become ______. Therefore, in an equilibrium system, the concentrations of the reactants and products remain ______.

A

Dynamic
Reactants
Unchanged

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8
Q

What must be true for a reaction to remain in equilibrium

A

The system must be closed

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9
Q

What is a closed system

A

A system which is isolated from its surroundings

So the temp., pressure, and conc. of reactants and products are unaffected by outside influences

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10
Q

What does the position of equilibrium indicate

A

The extent of the reaction

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11
Q

What does le Chatlier’s principle state

A

That when a system in equilibrium is subjected to an external change, the system readjusts itself to minimise the effect of that change

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12
Q

When an equilibrium system adjusts as a result of a change:

IF THERE ARE MORE PRODUCTS FORMED

A

The position of equilibrium has shifted to the right

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13
Q

When an equilibrium system adjusts as a result of a change:

IF THERE ARE MORE REACTANTS FORMED

A

The position of equilibrium has shifted to the left

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14
Q

What will changing the concentration of a reactant or product affect a reversible reaction

A

The rate of the forward or reverse reactions will change

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15
Q

Investigating changes to the position of equilibrium with concentration:

Chromate ions and Dichromate ions

A

The two solutions have different colours so it is easy to see any shift in the position of equilibrium
They are sensitive to changes in acid concentration
Chromate ions - yellow
Dichromate ions - orange

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16
Q

Experiment to show that the position of equilibrium can be changed by altering the concentrations of the reactants or products

ADDING AN ACID

A
  1. Add solution of yellow potassium chromate K2CrO4 to a beaker
  2. Add dilute sulfuric acid, H2SO4, dropwise until there is no further change. Solution turns an orange colour
  3. Add aqueous sodium hydroxide, NaOH(aq) until there is no further change. Solution changes back to a yellow colour
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17
Q

Explanation of the experiment to show that the position of equilibrium can be changed by altering the concentrations of the reactants or products (ADDING AN ACID)

A

The shift decreases the concentration of the added reactant H+
The position of equilibrium shifts to the left, making more of the H+ reactant.
A new position of equilibrium is established (Solution turns yellow as CrO42- forms)

18
Q

Change in temperature and equilibrium

What does the direction in which the equilibrium shifts depend on

A

The sign of ΔH
Forward and reverse directions have the same value for the enthalpy change - but the signs are opposite
An increase in temperature shifts the equilibrium position in the endothermic direction (ΔH is positive)
A decrease in temperature shifts the equilibrium position in the exothermic direction (ΔH is negative)

19
Q

What colour is the solution of cobalt chloride and water

A

Pink

20
Q

Experiment to investigate the changes to the position of equilibrium with temperature

A
  1. Dissolve cobalt chloride in water in a boiling tube. Add a small quantity of hydrochloric acid. Place boiling tube in iced water, solution is pink
  2. Set up boiling water bath and transfer boiling tube into boiling water. Solution turns a blue colour
  3. Transfer boiling tube back to iced water. Solution changes back to pink colour
21
Q

In boiling water, you are increasing the heat energy of the system. This causes position of equilibrium to shift to minimise change:

A

As forward reaction is endothermic (ΔH is positive), position of equilibrium shifts to right in endothermic direction, to take heat energy in and minimise increase in temperature
Solution turns blue colour

22
Q

Increase temperature shifts in…

A

…the endothermic direction

23
Q

Decrease in temperature shifts in…

A

…the exothermic direction

24
Q

In an exothermic forward reaction, ΔH is…

A

…negative

25
Q

In an endothermic forward reaction, ΔH is…

A

…positive

26
Q

How does equilibrium change if the temperature in an exothermic reaction increases

A

The position of equilibrium shifts to the left

More reactants are made

27
Q

How does equilibrium change if the temperature in an exothermic reaction decreases

A

Position of equilibrium shifts to the right,

More products are made

28
Q

How does equilibrium change if the temperature in an endothermic reaction increases

A

Position of equilibrium shifts to the right.

More products are made

29
Q

How does equilibrium change if the temperature in an endothermic reaction decreases

A

Position of equilibrium shifts to the left

More reactants are made.

30
Q

What is the pressure of a gas proportional to

A

Its concentration

31
Q

Increasing the pressure of the system will shift the position of equilibrium to the side with…

A

…the fewer molecules

32
Q

What colour is nitrogen dioxide NO2

A

Brown

33
Q

What colour is dinitrogen tetroxide N2O4

A

Colourless

34
Q

Does a catalyst change the position of equilibrium

A

NONONO

35
Q

What does a catalyst do

A

Speeds up the rates of the forward and reverse reactions

Increases the rate at which an equilibrium is established however DOES NOT change the position of equilibrium

36
Q

What can le Chatelier’s principle be used for

A

Predicting the best conditions of temperature and pressure to force the equilibrium to the right in order to produce the maximum yield of ammonia

37
Q

What conditions does a typical ammonia plate operate under

A

Compromise conditions using a high enough temp. to give a reasonable rate without shifting the equilibrium position too fat away from ammonia and back to the reactiants.
Ensures ammonia achieved quickly, cheaply and safely

38
Q

Typical temperatures and pressures used in an ammonia factory

A

350-500°C

100-200atm

Catalyst is also used (iron)

39
Q

How do they improve the efficiency of ammonia factories

A

Unreacted nitrogen and hydrogen are recycled repeatedly so nearly all the nitrogen and hydrogen used is eventually converted into ammonia

40
Q

What percentage of the nitrogen and hydrogen in an ammonia factory is converted to ammonia

A

15%

A Level Chemistry (OCR) Module 3 (15 decks)

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