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Chemistry > equilibria > Flashcards

equilibria Flashcards

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1
Q

under what conditions can a reaction reach dynamic equilibrium

A

in a closed system

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2
Q

what are the two characteristics of a system in dynamic equilibrium?

A

-the rate of the forward reaction is equal to the rate of the reverse reaction
-the concentration of the reactants and products remain constant

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3
Q

what is le chatelier’s principle?

A

if the conditions of a dynamic equilibrium in a closed system changed, the position of equilibrium will shift to oppose that change

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4
Q

what conditions can alter the equilibria of reactions?

A

concentration
pressure
temperature

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5
Q

what does a catalyst do to the position of equilibrium?

A

a catalyst has no effect on the position of equilibrium

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6
Q

how does a catalyst affect the reaction?

A

it alows the system to reach dynamic equilibrium more quickly by increasing the rate of the forward and reverse reaction by the same amount

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7
Q

what do these brackets ([ ]) represent?

A

concentration of

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8
Q

what does the position of equilibrium represent

A

concentration of reactants and products

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9
Q

what does it mean when the position of equilibrium is in the middle?

A

concentration of reactants and products are equal

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10
Q

what does it mean when the position of equilibrium is to the right?

A

the concentration of products is higher than the concentration of reactants

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11
Q

what does it mean when the position of equilibrium is to the left?

A

the concentration of reactants is higher than the concentration of products

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12
Q

what would happen to the position of equilibrium if the concentration of products increases?

A

shifts left (favours reactants)

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13
Q

what would happen to the position of equilibrium if the concentration of reactants decreases?

A

shifts left (favours reactants)

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14
Q

what would happen to the position of equilibrium if the concentration of products decrease?

A

shifts right (favours products)

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15
Q

what would happen to the position of equilibrium if the concentration of reactants increases?

A

shifts right (favours products)

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16
Q

in what reactions do changes in pressure affect the equilibrium position?

A

in reactions which contain at least one gas

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17
Q

what effect of changes in pressure have on a reaction with the same number of moles of gas on each side of the equation

A

pressure changes will not affect the dynamic equilibrium

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18
Q

what happens when the pressure is increased?

A

the position of equilibrium shifts to the side with the least amount of moles

19
Q

what happens when the pressure is decreased?

A

the position of equilibrium shifts to the side with more moles

20
Q

what is the shift in equilibrium dependent on if a reaction experiences a change in temperature

A

enthalpy change

21
Q

what will the forward and reverse reaction be if the enthalpy change is negative?

A

the forward reaction is exothermic
the reverse reaction is endothermic

22
Q

what happens to the position of equilibrium if the temperature increased?

A

shifts in the endothermic direction.
the equilibrium opposes the change by favouring the reaction that absorbs heat energy, lowering the temperature

23
Q

what happens to the position of equilibrium if the temperature decreased?

A

shifts in the exothermic direction.
the equilibrium opposes the change by favouring the reaction that releases heat energy, increasing the temperature

24
Q

what effect of the position of equilibrium would changes in temperature gave on a reaction with an enthalpy change of 0

A

if the enthalpy change is 0, changes in temperature will not have an effect on the position of equilibrium

25
Q

how does increasing the concentration of iodine effect the Kc for this reaction:
I2 + 2OH- ⇌ I- + IO- + H20

A
26
Q

why are the temperatures and pressures used in the haber process (N2 +3H2 ⇌ 2NH3 ) considered to be a compromise?

A

high pressures/ low temperatures increases the rate of the forward reaction and increases the yield of NH3 produced
maintaining high pressures is expensive (requires specialist equipment to handle safely)
and low temperatures decrease the rate of reaction

27
Q

why is a catalyst used in the haber process?

A

a catalyst would not affect the yield but they increase the rate of reaction

28
Q

how and why is the concentration of ammonia in the haber process kept low

A

NH3 is constantly removed from the reaction mixture by condensing (it has a high bp due to H bonds)
decreasing [NH3] causes more to be produced

29
Q

how are the concentrations of N2 and H2 kept high during the Haber process?

A

unreacted H2 and H2 are recycled to maintain high [ ]

30
Q

what is the equilibrium constant/Kc?

A

describes the state of equilibrium with respect to the concentrations of reactants and products

31
Q

what is the Kc expression if the reaction is aA +bB ⇌ cC + dD

A

kc= [C]^c [D^d]/ [A]^a [B]^b

32
Q

what is a homogenous reaction?

A

all the molecules are in the same phase

33
Q

what are the units for concentration?

A

mol dm^-3

34
Q

equation for concentration?

A

concentration= mol / volume (dm^3)

35
Q

what does 1/moldm^3 mean?

A

mol^-1 dm^3

36
Q

what does moldm^-3 x moldm^-3 /1 mean

A

mol^2 dm^-6

37
Q

what does it mean when Kc = 1?

A

equilibrium is in the middle

38
Q

what does it mean when Kc> 1?

A

equilibrium lies towards the products

39
Q

what does it mean when Kc< 1?

A

equilibrium lies towards the reactants

40
Q

what does it mean if the same reaction has a different equilibrium constant?

A

the temperature for the reaction is different

41
Q

what factor affects the Kc?

A

temperature

42
Q

what happens to the Kc if the temperature increases when the enthalpy change for the reaction is -90kJmol^-1?

A

if temperature increases, the reaction will favour the endothermic direction, therefore favouring the reactants
[reactants] increases
[products] decreases
so Kc decreases

43
Q

what happens to the Kc if the temperature decreases when the enthalpy change for the reaction is -90kJmol^-1?

A

if temperature decreases, the reaction will favour the exothermic direction and therefore the products
[products] increases
[reactants] decrease
Kc increases

44
Q
A

Chemistry (10 decks)

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