Le Chatelier's Principle #1
When products are added to a system at equilibrium, which direction would equilibrium shift to?
Shifts to left.
Favors reactants.
Which of the following is true about the following reversible reaction in physical (phase) equilibrium at 100oC?
H2O(l) ⇌ H2O(g)
a. the rate of crystalizing equals the rate of dissolving
b. the concentrations of liquid water and gaseous water are equal
c. the rate of freezing equals the rate of melting
d. the rate of condensation equals the rate of vaporization
D
Which statement(s) is/are true for a mixture of ice and liquid water at equilibrium?
a. The rates of melting and freezing are equal.
b. The amounts of ice and water are equal.
c. Both a and b are correct
d. Neither a nor b are correct
a
Which statement concerning a chemical reaction at equilibrium is not correct?
A. The concentrations of reactants and products remain constant.
B. Equilibrium can be approached from both directions.
C. The rate of the forward reaction equals the rate of the reverse reaction.
D. All reaction stops.
D. All reaction stops.
What do the letters in an "ICE Box" Table stand for?
initial
change
equilibrium
When reactants are removed from a system at equilibrium, which direction would equilibrium shift to?
Favors reactants
N2 + 3 H2 ⇌ 2 NH3
An increase in pressure would cause the reaction to shift in which direction?
Right (Fewer moles)
What is the equilibrium constant expression for this reaction?
SnO2 (s) + 2 CO (g) ⇌ Sn (s) + 2 CO2(g)
[CO2]2
[CO]2
Why do we refer to chemical equilibrium as "dynamic"?
Reaction continues, even if the concentrations stay the same.
In terms of x, what would the change row look like for the following reaction if 4.00M BrCl is initially placed into an evacuated flask with no Br2 or Cl2?
Br2(g) + Cl2(g) ⇌ 2BrCl(g)
Br2 = +x
Cl2 = +x
BrCl = -2x
What will happen to the position of equilibrium if this reaction was put under less pressure?
Br2 (g) + Cl2 (g) ⇌ 2 BrCl(g)
∆H = +14 kJ/mol
No change (equal number of moles)
Which of the following would NOT cause the reversible reaction at equilibrium to shift to the left?
I2 (g) + 3 Cl2 (g) ⇌ 2 ICl3 (g) + heat
a. adding heat
b. increasing pressure
c. increasing concentration of ICl3
d. decreasing concentration of Cl2
B
An equilibrium mixture is analyzed and found to contain 0.62M N2, 0.50M H2, and 0.24M NH3. What is Kc for the reaction, N2(g) + 3H2(g) ⇌ 2NH3(g)
Kc = 0.74
What is the equilibrium constant expression for the following reaction?
I2 (g) + 3 Cl2 (g) ⇌ 2 ICl3 (g)
[ICl3]2
[I2][Cl2]3
In the following reaction, Br2(g) + Cl2(g) ⇌ 2BrCl(g), what is the value for "x" if no BrCl is initially introduced to an evacuated flask and the equilibrium concentration of BrCl is 0.46 M
x = 0.23 M
N2 + 3 H2 ⇌ 2 NH3
ΔH = +92kJ/mol
Which direction would equilibrium shift to when heat is added?
right (products side)
Which of the following equilibria reactions would not be affected by pressure changes at constant temperature?
A. 4 HCl(g) + O2(g) ⇌ 2 H2O(g) + 2 Cl2(g)
B. CO(g) + H2O(g) ⇌ H2(g) + CO2(g)
C. C2H4(g) + H2O(g) ⇌ C2H5OH(g)
D. PF3Cl2(g) ⇌ PF3(g) + Cl2(g)
B. CO(g) + H2O(g) ⇌ H2(g) + CO2(g)
Kc for the equilibrium reaction is determined at two different temperatures.
At 850°C, Kc = 1.1.
At 1700°C, Kc = 4.9.
Based on these values, is this reaction likely to be exothermic or endothermic and why?
Endothermic
(Higher temperature led to more products, T increase = K increase, direct relationship)
NH4SH (s) ⇌ NH3 (g) + H2S (g) Write the equilibrium expression.
What is Kc = [NH3] [H2S]
**Solids not included in equilibrium expression
For the reaction N2(g) + 3H2(g) ⇌ 2NH3(g) the initial [N2] is found to be 0.32 M and the initial [H2] is found to be 0.66 M. At a certain temperature and pressure the equilibrium concentration of H2 is found to be 0.30 M. What is Keq under these circumstances?
11
2 SO2(g) + O2 (g) ⇌ 2 SO3(g) ∆H = –200 kJ
According to the above information, what temperature and pressure conditions produce the greatest amount of SO3?
(High vs low for both temperature and pressure)
Temperature: Low
Pressure: High
The equation for a reaction used in the manufacture of nitric acid is
4 NH3 (g) + 5O2 (g) ⇌ 4NO (g) + 6H2O (g)
∆H = –900 kJ /mol
What changes would happen to the position of equilibrium AND the value of Kc when the temperature of the reaction is increased?
Shifts left.
Value of Kc decreases.
At a given temperature, an equilibrium mixture of the reaction 2 NO(g) + O2(g) <--> 2 NO2(g) contains 0.090 moles NO, 0.120 moles of O2, and 0.060 moles of NO2 in a 3.00 liter container.
The value of Kc is...
Kc = 11
0.0206 M CH3OH, 0.120 M carbon monoxide, and 0.282 M hydrogen at 500 K. Calculate the equilibrium constant at this temperature.
CO (g) + H2 (g) ⇌ CH3OH (g)
Calculate the Kc value and determine whether this equilibrium constant favors the formation of reactants or products.
Reactants (Kc = 0.609)
4.00 moles of chlorine and 4.00 moles of bromine are introduced to a 5.00 L flask. Calculate the equilibrium concentrations of all species in the following reaction at 300oC if Kc = 9.00
Br2(g) + Cl2(g) ⇌ 2BrCl(g)
[Cl2] = 0.32 M
[Br2] = 0.32 M
[BrCl] = 0.64 M