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.
2 CO2(g) ⇌ 2 CO(g) + 02(g) where Fe(s) is a catalyst and both forward and reverse reactions are accelerated. What happens to the equilibrium shift?
nothing (catalysts do not affect equilibrium)
What is the equilibrium constant expression for the following reaction?
I2(g) + 3 Cl2(g) ⇌ 2 ICl3(g)
K= [ICl3]2
[I2][Cl2]3
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?
Shifts to the left
Favors reactants
N2(g) + 3 H2(g) ⇌ 2 NH3(g)
An increase in pressure would cause the reaction to shift in which direction?
Right (system would favor making more product)
What is the equilibrium constant expression for this reaction?
SnO2(s) + 2 CO(g) ⇌ Sn(s) + 2 CO2(g)
K= [CO2]2
[CO]2
Which concentrations are used to calculate the value of Q of a chemical reaction system?
A. concentrations of reactants and products at a particular instant in time
B. initial concentrations of reactants and equilibrium concentrations of products
C. equilibrium concentrations of reactants and products
D. equilibrium concentrations of reactants and initial concentrations of products
A. *NOT* at equilibrium but at any given time
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. Because there are less moles on the product side, so the equilibrium shift would favor the right
An equilibrium mixture is analyzed and found to contain 0.62M N2, 0.50M H2, and 0.24M NH3. What is K for the reaction, N2(g) + 3H2(g) ⇌ 2NH3(g)
K = 0.74
If K=4 for the reaction I2(g) + 3 Cl2(g) ⇌ 2 ICl3(g), what would the equilibrium constant be for the reverse reaction?
K'=0.25 because it is the reciprocal of K.
(K'= 1)
K
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
N2(g) + 3 H2(g) ⇌ 2 NH3(g)
ΔH = +92kJ/mol
Which direction would equilibrium shift to when heat is added?
Right (products side) since N2(g) + 3 H2(g) + energy ⇌ 2 NH3(g) is endothermic. Adding a reactant would shift the equilibrium towards making more products/right
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. Because there are the same amount of moles on both sides
K for the equilibrium reaction is determined at two different temperatures.
At 850°C, K = 1.1.
At 1700°C, K = 4.9.
Based on these values, is this reaction likely to be exothermic or endothermic?
Endothermic
Since increase in temp = increase in K, and K>1 favors products. Heat is a reactant, so an increase in temperature favors the forward reaction in endothermic processes, thus increasing the K value
NH4SH(s) ⇌ NH3(g) + H2S(g)
Write the equilibrium expression.
K = [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 K under these circumstances?
K = 11
2 SO2(g) + O2(g) ⇌ 2 SO3(g) ∆H = –200 kJ
According to the above information, predict what produces the greatest amount of SO3 in terms of A) temperature and B) pressure? (high vs. low)
A) Temperature: Low, since 2 SO2(g) + O2(g) ⇌ 2 SO3(g) + energy, so low temp would shift the equilibrium to the right side (therefore making more products)
B) Pressure: High, the side of SO3 has less moles so we should increase pressure to shift the equilibrium to the right
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
Temperature has decreased. What changes would happen to A) the position of equilibrium AND B) the value of K?
4 NH3(g) + 5O2(g) ⇌ 4NO(g) + 6H2O(g) + energy
A) Shifts right. 'Product' has been decreased so we must make more
B) Value of K increases. (shift to the right means K>1, favors products)
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 L container.
Find A) the value of K and B) tell me how it reflects the equilibrium position.
A) K = 11
B) K>1, favors the products (shifts to the right)
CO(g) + H2(g) ⇌ CH3OH(g)
We found the concentrations 0.0206 M CH3OH, 0.120 M carbon monoxide, and 0.282 M hydrogen.
A) Calculate the reaction quotient Q at this temperature when the K value is 0.37 and B) determine how we get to equilibrium.
A) Q=2.16.
B) Because Q > K, the system is not at equilibrium and will shift toward the reactants (to the left) to reach it.
4.00 moles of NH3(g) and 4.00 moles of H2S(g) are introduced to a 5.00 L flask. Calculate the equilibrium concentrations of all species in the following reaction at 300C if K=9.00.
NH4SH(s) ⇌ NH3(g) + H2S(g)
[NH3] = 3.00 M
[H2S] = 3.00 M
**Do not include NH4SH(s)