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Chemistry > Equilibrium > Flashcards

Equilibrium Flashcards

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1
Q

What is meant by chemical equilibrium?

A

State in which the rate of forward reaction is equal to rate of reverse reaction

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2
Q

Why is chemical equilibrium described as a dynamic state?

A

Both reactions are continuously occurring, both continue

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3
Q

State Le Châtelier’s principle

A

If “stress” is applied to system at equilibrium, system reacts to relieve stress applied

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4
Q

Write the equilibrium constant expression of

N2O4 ->2NO2

A

[NO2]^2
———
[N2O4]

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5
Q

The colour of equilibrium mixture is paler at 0 degrees celsius than at T, where T > 0 degrees celcius
Explaining your reason, deduce whether the decomposition of dinitrogen tetroxide into nidtogen dioxide is an exothermic or an endothermic reaction
N204 -> 2NO2
Colourless Dark Brown

A

Endothermic
At lower temperature, rxns try to minimise effect of reduced temp so equilibrium shifts in direction that produces heat, which is exothermic which is a forward reverse reaction, [more N2O4 is produced]
At higher temperature, rxns try to minimise effect of higher temperature so equilibrium shifts in direction that absorbs heat. Since forward reaction is exothermic, more NO2 is made

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6
Q

Would there be a change in the value of Kc at T If a different initial concentration is used?

A

No, KC constant is at given temperature

It will only change if temperature is changed

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7
Q

Use le Châtelier’s principle to predict and explain the conditions of temperature and pressure that would maximise the yield of C
A + B -> C

A

Low temperature -
Favours forward reaction which is exothermic, more of C is produced
High pressure -
Favours fewer molecules in forward reaction, more of C produced

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8
Q

Why is a low temperature not used industrially

A

Reaction rate is too slow, uneconomical at low temperature

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9
Q

State and explain the effect of the presence of the catalyst on the equilibrium yield of the product

A

None, as it alters the rate of forward reaction and reverse reactions equally
[causes rxns to reach equilibrium faster but does not change position of equilibrium]

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10
Q

The graph shows the relationship between temperature and kc for this equilibrium
A -> B + C
Deduce whether the dissociation or gas A is exothermic or endothermic

A

Endothermic
Kc increases with temperature and at high temperature reaction shifts to right to oppose stress and therefore is endothermic

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11
Q

Explain how an increase in temperature would affect the pressure of equilibrium mixture
A -> B + D

A

Equation will shift to right [forward reaction] which will decrease pressure of equilibrium [alter, and go to side with fewer molecules]

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12
Q

What effect would an increase in temperature and pressure have on the value of kc for this reaction
2NO -> N2 + O2 <> H = -183 KJ

A

Temp - If reaction is exothermic, increasing temp will reduce kc value as reaction shifts in backward direction to oppose added heat
Pressure - no effect, only temp change affects kc constant

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13
Q

When you increase the temperature what does it favour?

A

Endothermic

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14
Q

When you decrease the temperature what does it favour

A

Exothermic

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15
Q

How to determine if a reaction is exothermic or endothermic

A

If temperature decreases to get products of forward reaction, the forward reaction is exothermic
If temperature increases to get products of forward reaction, the forward reaction is endothermic
Talk about products increasing!!

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16
Q

Identify one industrial problem associated with the use of high pressures

A

Danger of leaks, danger of explosions, high costs

17
Q

H2 + I2 -> 2HI
Colourless purple colourless
When the colour of the mixture has become pale pink, has reaction ceased? [stopped] explain

A

No, chemical equilibrium is at dynamic state [continuously occurring]

18
Q

H2 + I2 -> 2HI
Colourless purple colourless
Use le châtelier’s principle to predict and explain the effect of a decrease in temperature on the yield of hydrogen iodide

A

Decrease in yield

Reaction tries to minimise effect of reduced temperature and equilibrium shifts in reverse

19
Q

H2 + I2 -> 2HI
Colourless purple colourless
Colourless purple colourless
Use le châtelier’s principle to predict and explain the effect of a decrease in temperature on the intensity of colour of the equilibrium mixture

A

More intense, darker

Reaction tries to minimise effect of reduced temperature and equilibrium shifts in reverse

20
Q

H2 + I2 -> 2HI
Colourless purple colourless
What change, if any, will an increase in the pressure on the equilibrium mixture have on the yield of hydrogen iodide? Explain

A

No change, equal number of molecules on both sides

21
Q

What effect does an increase in pressure have?

A

[opposite - side with fewer molecules]

System alters to oppose stress to side with fewer molecules

22
Q

What effect does a decrease in pressure have on an equilibrium reaction?

A

[think of opposite - side with more molecules]

The system alters to oppose stress, and moves to side with more molecules

23
Q

Have to explain the temperature -

A
  • State whether it’s exothermic or endothermic

- Oppose stress

24
Q

A + B - C + D

What occurs when concentration of A increases?

A

System alters to minimise effect and equilibrium shifts to right and more of C and D produced

25
Q

A + B - C + D

What occurs when concentration of C increases?

A

System alters to minimise effect, equilibrium shifts to left therefore more of A and B produced

26
Q

What happens if we increase the volume of the container?

A

Causes decrease in pressure

27
Q

What happens if we decrease the volume of the container?

A

Increases the presssure

28
Q

PCl3 + Cl2 - PCl5

What would the effect on concentration of PCl5 in equilibrium mixture when you introduce more PCl3 into mixture

A

If more PCl3 is introduced into the container, the equilibrium will shift to the right to absorb increase. Therefore the concentration of PCl5 will increase

29
Q

PCl3 + Cl2 - PCl5

What would the effect on concentration of PCl5 in equilibrium mixture when pressure is increased?

A

The equilibrium shifts to the aids with smaller amount of molecules to oppose stress, therefore is a forward reaction and PCl5 concentration increases

30
Q

PCl3 + Cl2 - PCl5
What would the effect on concentration of PCl5 in equilibrium mixture when temperature increases and the forward reaction is exothermic

A

We are told the forward reaction is exothermic which implies that the reverse reaction is endothermic. If the temperature is increased, the equilibrium will be shifted in the reverse direction in order to absorb this heat. Therefore, concentration of PCl5 will decrease

31
Q

Give an example of an industrial application of le chatelier’s principle

A

The Haber Process - manufacture of ammonia

32
Q

When the colour of the mixture becomes pink has the reaction ceased?

A

No, dynamic balance - continuously occurring

33
Q

What effect would a decrease in temperature have on the colour intensity of the equilibrium mixture
Colourless + purple -> colourless
Where forward reaction endothermic

A

More intense colour

34
Q

Describe what is observed when a small amount of sodium carbonate is added to a sample of ethanoic acid. Write a balanced equation for this reaction

A

Fizzing as CO2 is produced

2CH3COOH + Na2CO3 -> 2CH3COONa + CO2 + H20

35
Q

What occurs when the concentration is increased

A

Go opposite direction to use up excess of what is being increased

36
Q

What occurs when the concentration is decreased?

A

The opposite side increased to make up for what is being removed

37
Q

The addition of a catalyst which is specific to this reaction did not affect the position of the equilibrium. Why?

A

Catalyst alters rate of forward reaction and reverse reaction to same extent

38
Q

How can the colour change caused by the addition of HCL to cobalt chloride be reversed?

A

Add water

39
Q

I2 + I- -> i3-
State and explain the effect on the equilibrium concentration of triiodide ions of adding a substance that reacts with iodine eg, starch

A

concentration of triiodide ions decreases

reaction shifts to the left to combat stress

Chemistry (15 decks)

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