Chemical Equilibria Flashcards

1
Q

When is a system in equilibrium?

A

When the rate of the forward reaction is equal to the rate of the reverse reaction

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2
Q

When does a reaction system remain in equilibrium?

A

as long as the system is located (or closed)

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3
Q

What is a dynamic system?

A

one where reactants are being used up to form products and products are breaking down to form reactants but no change is observed in the reaction mixture; macroscopic properties (temperature and pressure) remain constant.

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4
Q

What is the position of equilibrium?

A

extent of a reaction when equilibrium is established

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5
Q

What are the features of a system at equilibrium?

A

-Rate of the forward reaction is equal to the rate of the backward reaction
-Concentration of reactants and products remains constant (*but is constantly moving)
-Systems are isolated
-Macroscopic properties remain constant (temp and pressure)

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6
Q

what are the two different types of equilibrium system?

A

Homogenous and Heterogeneous

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7
Q

What is heterogeneous equilibrium?

A

reactants and products are in different phases (states) (e.g. thermal decomposition)

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8
Q

What is homogenous equilibrium?

A

reactants and products are in the same phase (state)

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9
Q

What is [A]?

A

concentration of chemical A in
moldm-3

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10
Q

What is Kc?

A

the equilibrium constant-product of the concentrations of products over the product of the concentrations of reactants gives a ratio and shows how far towards the right or left a reaction lies when a reaction is at equilibrium;

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11
Q

What are stoichiometric ratios used to give the the kc equations?

A

the power?

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12
Q

what type of equilibria doe kc deal
with?

A

homogeneous

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13
Q

what does the larger value for the Kc mean?

A

The more the reaction has gone to completion

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14
Q

what does a large kc greater than one mean?

A

products are “favoured”; equibrium lies towards the right.

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15
Q

what does a small Kc less than one mean?

A

reactants are “favoured”; equilibrium lies towards the left.

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16
Q

when will an equilibrium system only remain in equilibrium?

A

When it is isolated

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17
Q

What happens once the conditions of equilibrium are changed?

A

The system will no longer be in equilibrium

18
Q

What are the conditions that affect equilibrium?

A

-temp
-pressure
-conc

19
Q

What is Le Chatelier’s principal?

A

When a system under dynamic equilibrium is subjected to a change, the equilibrium will shift so as to oppose the change

20
Q

what happens if the concentration of the reactants are increased? (in dynamic equilibrium)

A

They equilibrium shifts to the right hand side The yield of the product will increase

21
Q

what happens when the concentration of products are decreased? (in dynamic equilibrium)

A

-The equilibrium shifts to the right hand side
-The yield of the product will increase

22
Q

What are affected by change in pressure?

A

gases

23
Q

what does an increase in pressure of an equilibrium mixture lead to?

A

the equilibrium moving so as to decrease the pressure.
-does this by decreasing the number of molecules. (Fewer moles = lower pressure so equilibrium shifts to the side with the least gas moles).

24
Q

what does a decrease in pressure of the equilibrium mixture lead to?

A

the equilibrium mixture leads to the equilibrium moving so as to increase the pressure. It does this by increasing the number of molecules. (more moles = higher pressure so equilibrium shifts to the side with the most gas moles)

25
Q

What will the temperature increased favour?

A

The endothermic reaction

26
Q

what will the temperature reduced favour?

A

the exothermic reaction

27
Q

what do catalysts do?

A

-reduce the activation energy of a chemical reaction and therefore cause reactions to be speeded up.

28
Q

What does a catalyst do to the position of equilibrium?

A

does not affect the position of equilibrium however; it will affect the rate at which equilibrium is established

29
Q

In industry why are theoretical conditions not always used and what are often used instead?

A

-these can prove to be uneconomical or lead to a slow rate of reaction
-compromise set of conditions are used to run the plant at a profit, whilst obtaining the best yield and rate.
-so theoretical conditions are modified

30
Q

what does a low temperature lead to and why? (modification)

A

-very slow rate of attainment of equilibrium
-because the reaction has a high activation energy due to the strength of the triple bond which has to be broken before the nitrogen can react.
However a high temperature would lead to a poor yield as the position of equilibrium would move to the left

31
Q

however what would a high temperature lead to? (composition)

A

a poor yield as the position of equilibrium would move to the left

32
Q

what is the compromise condition for pressure?

A

-Very high pressure will increase the rate and also the yield but there is a significant increase in the cost of the plant.
-High specification pumps are required to maintain high pressure and maintenance of these is costly

33
Q

how is the problem of low rate of reaction overcome?

A

by using a catalyst, which enables the reaction to occur, by a different route of lower activation energy

34
Q

What else can increase the rate?

A

increasing the temperature and sacicing a high percentage yield

35
Q

what happens on the formation of ammonia?

A

-ammonia is removed so that the system does not reach equilibrium
-increases rate of reaction

36
Q

what are the conditions used in common ammonia plant?

A

200atm
450°C

37
Q

what does 80% of ammonia production go into?

A

making fertiser such as ammonium sulfate

38
Q

what are smaller proportions of ammonia used for?

A

The production of nitric acid which in turn is used to make explosives and polymers such as nylon which is a polyamide

39
Q

what problems are associated with low/high pressure? (optimum theoretical conditions)

A

Low- Slow rate of reaction
High -Uses a large amount of energy/fuel, provides a safety risk

40
Q

what problems are associated with low/high pressure? (optimum theoretical conditions)

A

Low- Slow rate of reaction
High- Uses a large amount of energy/fuel, Provides a safety risk, Uses a large amount of energy/fuel