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A LEVEL - Chemistry (Both) > Topic 10 - Equilibrium I > Flashcards

Topic 10 - Equilibrium I Flashcards

1
Q

What is a reversible reaction?

A

A reaction that can go forward or backwards.

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2
Q

How do you show a reversible reaction in an equation?

A

Use an double arrow that points both ways in the equation.

See pg 118 of revision guide

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3
Q

What is dynamic equilibrium?

A

When the concentrations of reactant and products in a reversible reaction are constant, and the forward and backwards reactions happen at the same rate.

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4
Q

In dynamic equilibrium, what can be said about:
• The reaction rates
• The concentrations

A
  • The forward and backwards reactions happen at the same rate
  • The concentrations of the products and reactants stay constant (but not necessarily equal to each other)
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5
Q

In dynamic equilibrium, when there are more products than reactants, where does the position of the equilibrium lie?

A

To the right.

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6
Q

In dynamic equilibrium, when there are more reactants than products, where does the position of the equilibrium lie?

A

To the left.

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7
Q

Describe how dynamic equilibrium is reached from a system with just the reactants in at first.

A
  • As the reactants get used up, the forward reaction slows down
  • As more product is formed, the reverse reation speeds up
  • Eventually, the two happen at the same rate and dynamic equilibrium is reached
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8
Q

Where can a dynamic equilibrium be reached?

A

In a closed system.

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9
Q

What is the equilibrium constant?

A

A measure of how far to the left or right the equilibrium is in a particular system.

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10
Q

What is the symbol for the equilibrium constant?

A

Kc

‘c’ is subscript

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11
Q

What is a homogeneous system?

A

One in which everything is in the same physical state,

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12
Q

What is a heterogeneous system?

A

One in which not everything is in the same physical state.

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13
Q

In a homogeneous system, which reactants and products are used in the equation for Kc?

A

All of them.

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14
Q

Write an equation for Kc for the reaction:

aA + bB dD + eE

A

Kc = [D]^d [E]^e / [A]^a [B]^b

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15
Q

In the equation for Kc, what goes on the top and bottom?

A

Top: Products
Bottom: Reactants

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16
Q

In the equation for Kc, what do the square brackets and powers mean?

A
  • Square brackets: Concentration of each substance.

* Powers: Number of moles of each substance from equation.

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17
Q

In a heterogeneous system, which reactants and products are used in the equation for Kc?

A

All of them, except solids and pure liquids.

18
Q

Why are solids and pure liquids not included in the equation for Kc in a heterogeneous system?

A

Their concentrations stay constant throughout the reaction.

19
Q

Write an expression for the equilibrium constant for:

H2 (g) + I2 (g) 2HI (g)

A

Kc = [HI]^2 / [H2] [I2]

20
Q

Write an expression for the equilibrium constant for:

H2O (g) + C (s) H2 (g) + CO (g)

A

Kc = [H2] [CO] / [H2O]

21
Q

What are the units for the concentrations used in the eqution for Kc?

A

mol / dm3

22
Q

What are the units for Kc?

A
  • It depends.

* Divide the units on top of the euqtion by those on the bottom.

23
Q

Remember to practise writing out dynamic equilibrium equations.

A

Pgs 118-119 of revision guide.

24
Q

Do catalysts affect the equilibirum constant (Kc)?

A

No, they just speed up the rate at which dynamic equilibrium is reached.

25
Q

If the equilibirum shifts to the left, you get more…

A

Reactants

26
Q

If the equilibrium shifts to the right, you get more…

A

Products

27
Q

State Le Chatelier’s principle.

A

If there’s a change in concentration, pressure or temperature in dynamic equilibrium, the equilibrium will move to help counteract that change.

28
Q

What changes in conditions can cause a shift in the position of an equilibrium

A
  • Temperature
  • Concentration
  • Pressure
29
Q

How does increasing the concentration of a reactant affect equilibrium?

A
  • Equilibrium tries to get rid of extra reactant

* Forward reaction is favoured -> So the equilibrium shifts to the right

30
Q

How does decreasing the concentration of a reactant affect equilibrium?

A
  • Equilibrium tries to get produce extra reactant

* Backwards reaction is favoured -> So the equilibrium shifts to the left

31
Q

How does increasing the pressure affect equilibrium?

A
  • Equilibrium tries to reduce the pressure

* Equilibrium shifts to the side with fewer moles of gas

32
Q

How does decreasing the pressure affect equilibrium?

A
  • Equilibrium tries to increase the pressure

* Equilibrium shifts to the side with more moles of gas

33
Q

How does increasing the temperature affect equilibrium?

A
  • Equilibrium tries to reduce the temperature

* Endothermic reaction is favoured -> So equilibrium shifts in that direction

34
Q

How does decreasing the temperature affect equilibrium?

A
  • Equilibrium tries to increase the temperature

* Exothermic reaction is favoured -> So equilibrium shifts in that direction

35
Q

If the foward reaction is exothermic, the reverse reaction is…

A

Endothermic

36
Q

Does changing the pressure always change the position of equilibrium?

A

No, only if there are gases involved.

37
Q

When working out how a change in pressure will affect equilibrium, what must you look at?

A

The total number of MOLES of gas on each side, not just the number of gases on each side.
(i.e. Look at the numbers before each gas!)

38
Q

What is the equation for the production of ethanol in industry?

A

C2H4 (g) + H2O (g) C2H5OH (g)

39
Q

What are the conditions for the production of ethanol in industry?

A
  • 60-70 atm
  • 300*C
  • Phosphoric(V) acid catalyst
40
Q

C2H4 (g) + H2O (g) C2H5OH (g) ΔH = -46 kJ/mol

The reaction takes place at 60-70 atm, 300*C and with a phosphoric(V) acid catalyst. Explain the temperature used.

A
  • Forward reaction is exothermic, so low temperatures favour the forward reaction -> Better yield
  • But lower temperatures mean a slow rate of reaction
  • So 300*C is a compromise between maximum yield and rate of reaction
41
Q

C2H4 (g) + H2O (g) C2H5OH (g) ΔH = -46 kJ/mol

The reaction takes place at 60-70 atm, 300*C and with a phosphoric(V) acid catalyst. Explain the pressure used.

A
  • High pressure favours the forward reaction -> Better yield
  • High pressure also increases the rate of reaction
  • But high pressure is expensive to maintain
  • So 60-70 atm is a compromise between maximum yield (+ rate) and expense
42
Q

Remember to revise how to word industry equilibrium consition questions.

A

Pg 121 of revision guide

A LEVEL - Chemistry (Both) (21 decks)

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