Problem drill (Module: Chemical Equilibrium)
IJSO Training: Chemical Equilibrium
Problem drill
1.
Hydrogen (H2) and iodine (I2) react reversibly to give hydrogen iodide. Assume the
equilibrium constant of the following reaction at a particular temperature is 2.45.
H2(g) + I2(g)
2 HI(g)
What are the equilibrium concentrations of hydrogen and iodine if the mixture contains
0.35 mol dm-3 of hydrogen iodide at equilibrium, assuming that the concentrations of
hydrogen and iodine are the same?
2.
Hydrogen (H2) and iodine (I2) react reversibly to give hydrogen iodide. Assume the
equilibrium constant of the following reaction at a particular temperature is 2.45.
H2(g) + I2(g)
2 HI(g)
What are the equilibrium concentrations of hydrogen, iodine and hydrogen chloride if
the initial concentrations of H2, I2 and HI are 0.08, 0.06 and 0.01 mol dm-3, respectively?
3. Consider the reversible reaction of nitrogen monoxide and oxygen giving nitrogen
dioxide.
2 NO(g) + O2(g)
2 NO2(g)
If an equilibrating mixture contains 0.25 mol dm-3 of NO, 0.45 mol dm-3 of O2, and 0.18
mol dm-3 of NO2, what is the equilibrium constant at that particular temperature?
4. Barium sulphate (BaSO4) is an ionic compound that dissolves sparingly in water. In
water, the Ba2+(aq) ions and SO42-(aq) ions are in equilibrium with the solid BaSO4(s), and the
equilibrium constant is 1.08 x 10-10 at 25oC.
(a)
Write an equilibrium expression for the dissolution of BaSO4 in water.
(b)
Calculate the equilibrium concentrations of Ba2+(aq) and SO42-(aq) if 5.5 g of BaSO4
was added to 100 ml of water.
5. Beryllium hydroxide (Be(OH)2) is an ionic compound that dissolves sparingly in water.
In water, the Be2+(aq) ions and OH-(aq) ions are in equilibrium with the solid Be(OH)2 (s),
and the equilibrium constant is 6.92 x 10-22 at 25oC.
(a)
Write an equilibrium expression for the dissolution of Be(OH)2 in water.
(b)
Calculate the equilibrium concentrations of Be2+(aq) and OH-(aq) if 4.1 g of Be(OH)2
was added to 100 ml of water.
6. Hydrogen and iodine reacts reversibly and give hydrogen iodide as the product.
H2(g) + I2(g)
2 HI(g)
The equilibrium constant of the above reaction at 750K is 52.3. Suppose that a mixture
of 0.8 mol of H2(g), 0.45 mol of I2(g) and 1.0 mol of HI(g) is sealed into a 10.0L flask and
heated to 750K. Calculate the equilibrium concentrations of the three substances.
7. The dimerization of NO2 to give N2O4 is a reversible reaction. The forward reaction is
exothermic.
2 NO2(g)
N2O4(g)
What would be the effect on the equilibrium position if:
(a)
The reaction temperature is increased
(b)
The total pressure of the system is increased
(c)
More NO2 is added to the system.
Problem drill (Module: Chemical Equilibrium)
8. Carbon monoxide reacts reversible with chlorine to give COCl2 as the product. The
forward reaction is exothermic.
CO (g) + Cl2(g)
COCl2(g)
What would be the effect on the equilibrium position if:
(a)
The reaction temperature is decreased
(b)
The total pressure of the system is increased
(c)
More chlorine is added to the system.
9. Hydrogen reacts reversible with nitrogen to give ammonia.
Process for producing ammonia in industry.
N2(g) + 3 H2(g)
2 NH3(g)
It is the well-known Haber
 Ho = -92.2 kJ
State the effects on (i) the equilibrium, (ii) the amount of H2, an (iii) the amount of NH3
present in the system when each of the following changes is applied to the system.
(a)
(b)
(c)
(d)
Increasing the temperature of the system
Adding more N2 to the system.
Increasing the pressure of the system.
Adding a catalyst to the system to speed up the reaction.
10. Shown below is the chemical equation representing the reversible conversion between the
orange dichromate ions (Cr2O72-) and yellow chromate ions (CrO42-) in an aqueous
solution.
Cr 2O 72-(aq) + H2O(l)
Orange
2 CrO 42-(aq) + 2 H+(aq)
Yellow
State whether the equilibrium position will shift to left or right if the each of the following
change is applied to the system.
(a)
Adding dilute hydrochloric acid to the mixture
(b)
Adding calcium carbonate to the mixture
(c)
Diluting the mixture with water to half of its original concentration.