Chemical Equilibrium Test

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Chemical Equilibrium Test - 3

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Question 1
1 / -0

When a reversible reaction is at equilibrium, one of its products' concentration is decreased. The equilibrium state

A
shifts in the direction of backward reaction

B
shifts in the direction of forward reaction

C
is not affected

D
moves in either direction

Solution

According to the Lechatelier's principle when a system at equilibrium is subjected to a change, the equilibrium shifts in the direction so as to undo the change.
Therefore, if the concentration of product is decreased,the forward reaction takes place so as to increase the concentration.
Question 2
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If k₁ and k₂ are the respective equilibrium constants for the reactions (I) and (II), where (I) is 2NO and (II) is NO, then

A
k₂ = k₁

B
k₂ =

C
k₁ = 2k₂

D
k₁ = k₂

Solution

On squaring k₂, we get
The right side of (k₂)²_ⁱs equal to k₁.
So, (k₂)² = (k₁)
Or k₂ =
Question 3
1 / -0

For PCl₅ (g) PCl₃ (g) + Cl₂ (g); H = 22 k. cals, the dissociation of PCl₅ will be more on

A
increasing temperature

B
decreasing temperature

C
increasing pressure

D
increasing the concentration of chlorine

Solution

Endothermic reactions are favoured by increasing temperature.
Question 4
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The Haber's process for the manufacture of ammonia is usually carried out at 450–500°C. If the temperature of 250°C was used instead of 450–500°C, then

A
no NH₃ would be formed at all

B
the percentage of NH₃ in the equilibrium mixture would be too low

C
a catalyst would not be used at 250°C

D
the rate of formation of NH₃ would be too slow

Solution

Although formation of NH₃ by Haber's process is an exothermic reaction and is favoured at low temperatures, yet the required temperature for the combination of N₂ and H₂ should be 450–500°C in order to provide the activation energy for the process. If the temperature is 250°C, then the rate of formation of NH₃ would be too slow and above 500°C, and the equilibrium will shift towards the left.
Question 5
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Assertion: An increase in the volume of a system that results in a decrease in the total pressure will cause a shift to the side of the equilibrium with greater number of moles of the gas.
Reason: This counters the decrease in the total pressure.

A
Both A and R are true and R is the correct explanation of A.

B
Both A and R are true but R is not correct explanation of A.

C
A is true but R is false.

D
Both A and R are true.

Solution

According to Le Châtelier's principle, "The decrease in the total pressure will cause a shift to the side of the equilibrium with greater number of moles of the gas."
Question 6
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Assertion: A net reaction can occur only if a system is not at equilibrium.
Reason: All reactions occur to reach a state of equilibrium.

A
Both A and R are true and R is the correct explanation of A.

B
Both A and R are true but R is not correct explanation of A.

C
A is true but R is false.

D
Both A and R are false.

Solution

The law of chemical equilibrium define the direction in which a chemical reaction will proceed, as well as the quantities of reactants and products that will remain after the reaction comes to an end.
Question 7
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What is the relation between K_p and K_c in the following reaction?

N₂(g) + 3H₂(g) 2NH₃(g)

A
K_p = K_c

B
K_p = K_c - RT

C
K_p = K_c/(RT)²

D
K_p = K_c/(RT)^-²

Solution

The relation between K_p and K_c is given as:
K_p = K_c(RT)^Δn
K_p = equilibrium constant in terms of partial pressure
(Its unit is 'atm'.)
K_c = equilibrium constant in terms of concentration (molarity)
R = ideal gas constant (0.082 atm.L/K.mol)
T = absolute temperature (570 K)
Δn = Σn products - Σn reactants
Δn = (2) - (3 + 1) = -2
Thus, for the formation of NH₃, the correct relation between K_pand K_c is:
K_p = K_c(RT)^-2 or K_p = K_c/(RT)²
Question 8
1 / -0

For the reaction: H₂(g) + I₂(g) ⇌ 2HI(g), the equilibrium constants expressed in terms of concentration K_c and partial pressure K_p are related as

A
K_p = K_c(RT)²

B
K_p = K_c(RT)^-2

C
K_p = K_c

D
K_c = K_p(RT)

Solution

For the reaction
H₂(g) + I₂(g) ⇌ 2HI(g)
K_p = K_c (RT)^Δn
Δn = 2 - 2 = 0
So, K_p = K_c
(where, K_p and K_c are equilibrium constants in terms of partial pressures and concentrations.)
Question 9
1 / -0

PCl₃ (g) + Cl₂ (g) PCl₅ (g) K_c (250°C) for this reaction is 26. The value of K_pat the same temperature is

A
0.83

B
0.57

C
0.6

D
0.46

Solution

= 1 - (1 + 1) = - 1
K_p = K_c .
= 26 × (0.082 × 523)^-1 = 0.6
Question 10
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Which of the following reactions will proceed in forward direction if the volume of the container is increased?

A
H₂ + Cl₂2HCl

B
CaCO₃ CaO + CO₂

C
N₂ + 3H₂2NH₃

D
N₂ + 2O₂N₂O₄

Solution

If the total volume of a container is increased, this means that the total pressure is decreased. The equilibrium will then shift to the side with more moles of gases. In option 2, since CaO and CaCO₃ are solids, we can assume that their concentration are constant. But CO₂ is a gas. Therefore, in this case, the reaction will proceed in forward direction.
Question 11
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Which of the following changes will shift the given reaction towards the product?

l₂ (g) ⇌ 2l (g), (298 K) = +150 kJ

A
Increase in concentration of I

B
Decrease in temperature

C
Increase in temperature

D
Increase in total pressure

Solution

According to Le Chatelier's principle, increase in temperature will shift the equilibrium in favour of the endothermic process which in this case is the forward reaction.
Question 12
1 / -0

Two moles of PCl₅ are heated in a closed vessel of 2 L capacity. When the equilibrium is attained, 40% of it is found to be dissociated. What is K_c in mol/dm³?

A
0.532

B
0.267

C
0.133

D
0.174

Solution
Question 13
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The unit of Kc for the equilibrium reaction 2HIH₂+ I₂is

A
mol dm^-3

B
no unit

C
mol²dm^-6

D
mol^-1dm³

Solution

The unit of Kc for the given equilibrium reaction is = No unit.
Question 14
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In the reaction 3A + 2B 2C, the equilibrium constant K_cis given by

A

B

C

D

Solution

In the reaction 3A + 2B 2C, the equilibrium constant K_cis given by ^.
Question 15
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What is the equilibrium expression for the reaction P₄(s) + 5O₂ (g) P₄O₁₀(s)?

A

B

C
K_c = [O₂]⁵

D

Solution

The activity of solids(s) and liquids(l) is equal to one.
K can be written as follows.
K = [Products]^p/[Reactants]^r, where p and r are the reactant and product mole ratios.
Therefore, option (4) is the correct option.
Question 16
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One mole of a compound AB reacts with one mole of a compound CD according to the equation AB + CD AD + CB. When equilibrium was established, it was found that 3/4 mol each of reactants AB and CD had been converted to AD and CB, respectively. There was no change in volume. The equilibrium constant for the reaction is

A
9/16

B
1/9

C
16/9

D
9

Solution
Question 17
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The equilibrium constant for the reaction 2NO₂ (g) 2NO (g) + O₂ (g) is 2 10^-6. The equilibrium constant for the reaction 4NO(g) + 2O₂ (g) 4NO₂(g) at the same temperature would be

A
2.5 10^-5

B
4 10^-12

C
2.5 10¹¹

D
2 10⁶

Solution
Question 18
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If = 46 V, then the equilibrium constant of the reaction Cu(s) + 2Ag⁺(aq) Cu²⁺(aq) + 2Ag(s) is given as

A
2.4 10¹⁰

B
2.0 10¹⁰

C
4.0 10¹⁰

D
4.0 10¹⁵

Solution
Question 19
1 / -0

The equilibrium constant K_p for thermal dissociation of PCl₅ at 200°C is 1.6 atm. The pressure (in atm) at which it is 50% dissociated at the same temperature is

A
4.8

B
4.2

C
3.2

D
2.4

Solution
Question 20
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Which of the following has/have equilibrium constant as one?

A
1 only

B
2 only

C
Both 2 and 3

D
Both 1 and 3

E
None of these

Solution