Leah Firmstone
Quiz von , erstellt am more than 1 year ago

A level Chemistry A level Quiz am Equilibria Quiz, erstellt von Leah Firmstone am 26/02/2017.

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Leah Firmstone
Erstellt von Leah Firmstone vor fast 8 Jahre
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Equilibria Quiz

Frage 1 von 22

1

Dynamic Equilibrium: A situation in which the of a constant reaction mixture does not because both forward and backward reactions are proceeding at the same .

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    composition
    concentration
    rate
    change

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Frage 2 von 22

1

Which of the following are conditions which apply to all equilibria?

Wähle eine oder mehr der folgenden:

  • Equilibrium can only be reached in a closed system.

  • Equilibrium can only be reached if the reaction starts from the reactants on the left of the equation.

  • Equilibrium is a dynamic process which is reached when the rates of two opposing simultaneous processes are the same.

  • Equilibrium has been reached when the amounts of products and reactants in the equilibrium mixture is the same.

  • You can tell that equilibrium has been reached when the macroscopic properties of the system do not change with time (i.e. density, concentration, colour and pressure)

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Frage 3 von 22

1

Once equilibrium is reached the concentrations of the reactants and the products do not change.

Wähle eins der folgenden:

  • WAHR
  • FALSCH

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Frage 4 von 22

1

What can be said about the rates of the forwards and backwards reactions when equilibrium has been reached?

Wähle eine der folgenden:

  • They are equal and constant.

  • The rate of the reactions is zero as the reactions have stopped.

  • They are still changing.

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Frage 5 von 22

1

A + B <---> C + D
At the of the reaction the forward rate is fast, because A and B are . There is no because there is no C and D.
Then as the of C and D build up, the reverse reaction speeds up. At the same time the concentrations of A and B so the forward reaction .
A point is reached where exactly the same are changing from A and B to C and D as are changing from C and D to A and B. has been reached.

NB. An equilibrium can have any proportions of reactants and products. The proportions may be changed depending on the of the reaction, such as temperature, , and concentration. But at any given constant conditions the proportions of reactants and products change.

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    start
    plentiful
    reverse reaction
    concentrations
    decrease
    slows down
    number of particles
    Equilibrium
    mixture
    conditions
    pressure
    do not

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Frage 6 von 22

1

Le Chatelier's Principle: For a closed system in dynamic equilibrium, if a change is made the equilibrium will shift to increase that change.

Wähle eins der folgenden:

  • WAHR
  • FALSCH

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Frage 7 von 22

1

If you the concentration of one of the reactants, Le Chatelier's principle says that the will shift in the direction what tends to reduce the concentration of this reactant.
A(aq) + B(aq) <---> C(aq) + D(aq)
If you add some extra A (increase its ), the only way that the system can reduce the concentration of A is by it with B to form more C and D. So, adding more A uses up more B, more C and D, and moves the equilibrium to the . You end up with a proportion of products in the reaction mixture than before.

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    increase
    concentration
    reacting
    produces
    right
    greater
    equilibrium

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Frage 8 von 22

1

Pressure changes only affect reactions involving . Changing the overall pressure will only change the position of equilibrium of a gaseous reaction if there are a number of molecules on either side of the equation.

N204(g) <---> 2NO2
the pressure of a gas means that there are more molecules of it in a given volume - it is equivalent to increasing the of a solution.
If you increase the pressure on this system, Le Chatelier's principle tells us that the position of equilibrium will move to the pressure. This meas it will more to the because fewer molecules exert less pressure.

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    gases
    different
    Increasing
    concentration
    decrease
    left

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Frage 9 von 22

1

Increasing the pressure or decreasing the volume of a mixture of gases decreases the concentration of all the reactants and products by the same amount, not just one of them.

Wähle eins der folgenden:

  • WAHR
  • FALSCH

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Frage 10 von 22

1

The rate at which equilibrium is reached will be speeded up by increasing the pressure, as there will be more collisions in a given time.

Wähle eins der folgenden:

  • WAHR
  • FALSCH

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Frage 11 von 22

1

Increasing the temperature of a reaction will cause the equilibrium to shift in which direction?

Wähle eine der folgenden:

  • To favour the endothermic reaction

  • To favour the exothermic reaction

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Frage 12 von 22

1

What effect would adding a catalyst have on a reversible reaction in a closed system? (Choose TWO)

Wähle eine oder mehr der folgenden:

  • The position of equilibrium would shift to favour the forwards reaction.

  • The position of equilibrium would shift to favour the reverse reaction.

  • The position of equilibrium would not change.

  • Equilibrium would be reached faster.

  • The reaction would never reach equilibrium.

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Frage 13 von 22

1

80% of ammonia produced is used to make which product?

Wähle eine der folgenden:

  • Fertilisers

  • Synthetic fibers

  • Dyes

  • Explosives

  • Plastics

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Frage 14 von 22

1

N2(g) + H2(g) <---> NH3(g) [delta H = -92kJmol^-1]

Almost all ammonia is made by the process, in which the reaction above is the key step. A low temperature and high would give close to 100% conversion whereas low pressure and high temperature would give almost no . However, a compromise is used to ensure the rate of reaction is viable and the conditions safe. Most plants run at a pressure of around 20000kPa (c. atmospheres) and a temperature of about K (c. 450 celsius).
The raw materials for the Haber process are air (providing the nitrogen), water, and natural gas (methane). These provide the hydrogen by the following reaction:
(g) + H2O(g) ---> (g) + 3H2(g)
The nitrogen and hydrogen are fed into a converter in the ratio and passed over an catalyst.
The conversion is not at maximum as the conditions are not optimum (a is used) and the gases flow continuously over the catalyst so they do not spend long enough in contact with the catalyst to reach . Any unconverted reactants are through the converter to increase the yield.

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    3
    2
    Haber
    pressure
    ammonia
    200
    670
    economically
    CH4
    CO
    1:3
    iron
    compromise
    equilibrium
    recycled

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Frage 15 von 22

1

The most common source of ethanol for industrial use is the fermentation of sugars such as glucose.

Wähle eins der folgenden:

  • WAHR
  • FALSCH

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Frage 16 von 22

1

Fülle die Lücken, um den Text zu vervollständigen.

Ethanol is the alcohol in alcoholic drinks, but also has many uses for example making cosmetics, drugs, detergents, inks, and as a motor . At present the main source of ethanol for industrial use is from crude oil.
Ethanol is made by the hydration of ethene. The reaction is and is speeded up by a catalyst of acid absorbed on silica.
The equation is:
C2H4(g) + (g) <---> C2H5OH(g) [delta H = -46kJmol^-1]
Applying Le Chatelier's principle to this predicts the maximum yield will be produced with pressure, low temperature, and excess steam. However, there are practical problems: high pressure can cause ethene to polymerise; high pressure increases and danger; low temperature reduces the rate of reaction; too much steam dilutes the catalyst. Therefore in practise, conditions of about 570K and kPa are used. These give a conversion to ethanol of only around 5%, but the unreacted reactants are until about 95% conversion is obtained.

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Frage 17 von 22

1

Le Chatelier's principle tells us that the methanol synthesis reaction will give the highest yield at low temperature and high pressure.

Wähle eins der folgenden:

  • WAHR
  • FALSCH

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Frage 18 von 22

1

Which of the following is true?
The Kc of a reaction is...

Wähle eine der folgenden:

  • [products]/[reactants]

  • [reactants]/[products]

  • ([reactants]x[products])/2

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Frage 19 von 22

1

Kc > 1 -->
Kc = 1 -->
Kc < 1 -->

Klicke und ziehe, um den Text zu vervollständigen.

    equilibrium lies towards the products
    equal concentrations
    equilibrium lies towards the reactants

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Frage 20 von 22

1

The equilibrium constant (Kc) does not change with concentration or pressure, but it does when the temperature is changed.

Wähle eins der folgenden:

  • WAHR
  • FALSCH

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Frage 21 von 22

1

When can the number of moles of products and reactants be used to calculate the Kc instead of the concentrations?

Wähle eine der folgenden:

  • When all the products and reactants have different powers/indicies.

  • When there is only one product.

  • When all the products and reactants have equal volume.

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Frage 22 von 22

1

The Kc of the reaction between nitrogen monoxide (NO) and oxygen (O2) to form nitrogen dioxide (NO2) has no units.

Wähle eins der folgenden:

  • WAHR
  • FALSCH

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