Chapter 19 - Equilibrium Flashcards

1
Q

What is homogeneous equilibria?

A

When there are equilibrium species that are all in the same state

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2
Q

What is heterogeneous equilibria?

A

An equilibrium which contains species in different states or phases

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3
Q

How does the KC formula change for heterogeneous equilibrium?

A

The kc equation involves concentration but the concentration of solids and liquids stay constant so they are omitted from the formula.

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4
Q

How do you work out mole fraction?

A

Mole fraction = number of moles of A / total number of moles mixture

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5
Q

How is measuring equilibrium of gases different to mixtures in other states?

A

Equilibria is usually expressed as Kp. In terms of partial pressure as this is easier to measure than concentration. Kp is directly proportional to Kc.

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6
Q

How do you work out the partial pressure of a gas in a mixture?

A

Mole fraction A x total pressure p

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7
Q

What should the sum of the mole fractions and partial pressures equal?

A

Mole fractions = 1

Partial pressures = total pressure

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8
Q

What happens to solids and liquids in the Kc expression of heterogeneous equilibria?

A

Solids and liquids concentrations stays constant so they are omitted from the expression

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9
Q

Under what conditions can Kc change?

A

Kc only changes if temperature changes but stays the same with changes in concentration, pressure or in the presence of a catalyst

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10
Q

When increasing the temperature for an exothermic reaction what must happen to regain equilibrium at the different Kp?

(Explanations for Kc use concentration rather than partial pressure)

A

1) Kp is effected by temperature
2) Kp decreases with increasing temperature for exothermic reactions
3) Equilibrium shifts to the left increasing yield of reactants (state reactants)
4) Bottom of Kp expression increases
5) Equilibrium is re-established at the new value of Kp

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11
Q

When increasing the temperature for an endothermic reaction what must happen to regain equilibrium?

(Explanations for Kc use concentration rather than partial pressure)

A

1) Kp is effected by temperature
2) Kp increases with increasing temperature for endothermic reactions
3) Equilibrium shifts to the right increasing yield of products (state products)
4) Top of Kp expression increases
5) Equilibrium is re-established at the new value of Kp

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12
Q

What happens when the concentration of gaseous products are decreased?

What must happen to return to original Kc?

  • use partial pressure rather than conc for Kp
A

1) Kc does not change
2) When products are decreased the top of Kc expression is smaller (concentration is smaller)
3) Equilibrium shifts to the right increasing yield of products (state product)
4) Top of Kc expression increases
5) Kc is restored

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13
Q

What happens when the concentration of gaseous products are increased?

What must happen to return to original Kc?

  • use partial pressure instead of conc for Kp
A

1) Kc does not change
2) When products are increased the top of Kc expression is greater (concentration is greater)
3) Equilibrium shifts to the left increasing yield of reactants (state reactant)
4) Bottom of Kc expression increases
5) Kc is restored

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14
Q

What is the effect of a catalyst on the equilibrium constant?

A

1) Affect the rate of a chemical reaction but not the position of equilibrium
2) Speed up both the forward and reverse reaction in the equilibrium

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15
Q

How do you determine the Kc from experimental results?

A

1) Titrate the solution once it has reached equilibrium to find the equilibrium conc
2) use the ICE method

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15
Q

Qualititative effect of increasing temperature on exothermic reaction

A

1) Decreases the equilibrium constant
2) Decreases the equilibrium yield of products
3) Equilibrium position shifts to the left

15
Q

Qualititative effect of increasing temperature on endothermic reaction

A

1) Increased equilibrium constant
2) Increases the equilibrium yield of products
3) Equilibrium shifts to the right

16
Q

What is the effect of increasing pressure when there is the same number of moles of gaseous products and reactants on Kp?

A

1) The ratio stays the same

2) No effect on equilibrium