15.3.2 The Effect of Changing Amounts on Equilibrium Flashcards Preview

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Flashcards in 15.3.2 The Effect of Changing Amounts on Equilibrium Deck (12)
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1
Q

The Effect of Changing Amounts on Equilibrium

A
  • Le Châtelier’s principle can be used to predict how a system will respond to a change in the partial pressure (or concentration) of one of its components.
  • The reaction quotient (Q) and ICE diagrams (initial values, change, and equilibrium values) are used to quantify changes in equilibrium.
2
Q

note

A
  • A container of H 2 , I 2 , and HI was allowed to reach
    equilibrium. How would the partial pressures of the
    components be affected if additional H 2 were added to the system?
  • Le Châtelier’s principle states that a system in equilibrium that is subjected to a stress will react in a way that tends to relieve stress. Addition of a reactant (H 2 ) to a system already in equilibrium causes the equilibrium to shift toward products.
  • Partial pressures for initial conditions and after H 2 is added are given.
  • These values are placed into the K p and Q equations and the equations are solved.
  • Since Q < K p , the reaction must proceed to the right, thus increasing P HI and decreasing P H2 and P I2 until Q = K p .
  • What are P H2 , P I2 and P HI when the new equilibrium is established?
  • Values are entered into an ICE diagram (initial values, change, and equilibrium values) and solved with the
    quadratic formula. The quadratic formula yields two
    solutions (0.142 atm and 2.30 atm), but only one is physically meaningful. If x were 2.30 atm, the equilibrium partial pressure of H 2 (2.00 – x) would be negative—since this is impossible, x cannot be 2.30 atm.
3
Q

What is the expression for Q, the reaction quotient, for the following system?
N2(g) + 3H2(g) 2NH3(g)

A

Q = [ NH3 ]^2 / [ N2 ] [H2 ]^3

4
Q

Hydrogen gas combines with iodine gas to form hydrogen iodide gas in the following equilibrium reaction: H2(g) + I2(g) HI(g)
Suppose the reaction vessel contains these gasses at the following initial partial pressures:
PH2 = 0.132 atm
PI2 = 1.85 atm
PHI = 2.15 atm
Which of the following represents the equilibrium partial pressure expressions for these gasses?
Assume Kp > 1

A
PH2 = (0.132-x) atm
PI2 = (1.85-x) atm
PHI = (2.15+2x) atm
5
Q

Which of the following does NOT complete the sentence correctly?

Le Châtelier’s principle _____________

A

says that if you increase the concentration of a product, the equilibrium will shift to the right.

6
Q

Suppose that the equilibrium constant, KP, (at 340°C) for the following reaction is 490.

PCl5(g) PCl3(g) + Cl2(g)

If the partial pressure of PCl5 is 0.0019 atm and the partial pressure of Cl2 is 0.53 atm, what is the partial pressure of PCl3?

A

1.76 atm

7
Q

Look at the reaction of H2 and I2 to form HI
H2(g) + I2(g) 2HI(g)
The expression for the reaction quotient, Q is [HI]^2/[H2][I2]. At equilibrium, Q = Keq = 92.6 Suppose that you have PH2 = 0.208 atm, PI2 = 0.101 atm, and PHI = 3.01 atm. Suppose that you add H2 until its concentration reaches 0.444 atm. What is the correct expression for Kp if you use x for the change in concentration of H2

A

KP = 92.6
= [HI]2 / [H2 ] [ I2 ]
= (3.01 + 2x)2 / (0.444 − x) (0.101 − x)

8
Q

Look at the reaction
H2(g) + I2(g) 2HI(g). At equilibrium, Q = Keq = 92.6 Suppose that you have PH2 - 0.217 atm, PI2 = 0.121 atm, and PHI = 2.77 atm, I2 is added until tis concentration reaches 2.33 atm. Letting x be the change in partial pressure of H2, the final quadratic equation for x is 88.6x^2 - 247.2x = 39.2 = 0. What tare the final equilibrium concentrations of all three components

A

[HI] = 3.11 atm; [H2 ] = 0.047 atm; [ I2 ] = 2.16 atm

9
Q

What is the expression for Q, the reaction quotient, for the following reaction?
4NH3(g) + 5O2(g) 4NO(g) + 6H2O(g)

A

Q = [ NO]^4 [H2O]^6 / [O2 ]^5 [ NH3 ]^4

10
Q

At equilibrium, there are 0.125 atm O2, 0.234 atm of NH3, 1.23 atm of NO, and 0.68 atm of H2O. The partial pressure of O2 is then increased to 0.232 atm.

4NO(g) + 6H2O(g) 4NH3(g) + 5O2(g)

Use Le Châtelier’s principle to decide which of the following statements is not correct.

A

At final equilibrium, [ NH3 ] is (0.234 + (4/5) x), where x is the change in concentration (or partial pressure) for O2, as the reaction reaches a new equilibrium.

11
Q

Look at the following reaction.

4NH3(g) + 5O2(g) 4NO(g) + 6H2O(g)

Use Le Châtelier’s principle to decide which statement is correct.

A

Removing some NO from the system would cause more H2O to form.

12
Q

Which statement is NOT correct about Q, the reaction quotient?

A

If Q < Keq, the amount of products at equilibrium is greater than the amount of reactants at equilibrium.

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