21. What is the effect of increasing pressure on the equilibrium of the following reaction?
PCl5(g)⇌PCl3(g)+Cl2(g)PCl5(g)⇌PCl3(g)+Cl2(g)**
a) The equilibrium shifts to the right.
b) The equilibrium shifts to the left.
c) The equilibrium constant increases.
d) The equilibrium does not shift.
Answer: b) The equilibrium shifts to the left.
Explanation:
Increasing pressure favors the side with fewer gas molecules. In this reaction, the left side (PCl55) has fewer moles of gas compared to the right side (PCl33 + Cl22).
22. The addition of which of the following to a solution of acetic acid will decrease the ionization of acetic acid?
a) NaOH
b) HCl
c) CH33COONa
d) NaCl
Answer: c) CH33COONa
Explanation:
Adding CH33COONa introduces a common ion (acetate ion, CH3COO−CH3COO−), which suppresses the ionization of acetic acid due to the common ion effect.
23. If the KcKc value for a reaction is very large, what can be inferred about the reaction?
a) The reaction favors the formation of products.
b) The reaction favors the formation of reactants.
c) The reaction is very slow.
d) The equilibrium is not achievable.
Answer: a) The reaction favors the formation of products.
Explanation:
A large KcKc value indicates that the concentration of products is much higher than that of the reactants at equilibrium, meaning the reaction favors product formation.
24. The dissociation constant of a weak acid is given as 1×10−51×10−5. What is the pKa value of the acid?
a) 5
b) 10
c) 1
d) 0.5
Answer: a) 5
Explanation:
The pKapKa is the negative logarithm of the dissociation constant KaKa. So, pKa=−log(1×10−5)=5pKa=−log(1×10−5)=5.
25. Which of the following statements is true for a system in dynamic equilibrium?
a) The forward and reverse reactions have stopped.
b) The concentrations of reactants and products are changing.
c) The rates of the forward and reverse reactions are equal.
d) The equilibrium constant depends on the concentrations.
Answer: c) The rates of the forward and reverse reactions are equal.
Explanation:
In dynamic equilibrium, the forward and reverse reactions continue to occur, but their rates are equal, so the concentrations of reactants and products remain constant.
26. For the reaction H2(g)+I2(g)⇌2HI(g)H2(g)+I2(g)⇌2HI(g), if the concentration of H2H2 is doubled, what happens to the equilibrium constant KcKc?
a) KcKc increases
b) KcKc decreases
c) KcKc remains the same
d) KcKc becomes half
Answer: c) KcKc remains the same
Explanation:
The equilibrium constant KcKc is only affected by temperature. Changes in the concentration of reactants or products do not affect the value of KcKc, only the position of equilibrium.
27. Which of the following reactions will shift towards the right if the temperature is increased?
a) N2(g)+3H2(g)⇌2NH3(g)N2(g)+3H2(g)⇌2NH3(g) (exothermic)
b) N2O4(g)⇌2NO2(g)N2O4(g)⇌2NO2(g) (endothermic)
c) 2SO2(g)+O2(g)⇌2SO3(g)2SO2(g)+O2(g)⇌2SO3(g) (exothermic)
d) C(s)+O2(g)⇌CO2(g)C(s)+O2(g)⇌CO2(g) (exothermic)
Answer: b) N2O4(g)⇌2NO2(g)N2O4(g)⇌2NO2(g) (endothermic)
Explanation:
Increasing the temperature favors the endothermic reaction by shifting the equilibrium toward the products (the right side). Therefore, the reaction that absorbs heat (endothermic) will shift right.
28. Which of the following would increase the solubility of a gas in water?
a) Increasing the temperature
b) Decreasing the pressure
c) Increasing the pressure
d) Adding a catalyst
Answer: c) Increasing the pressure
Explanation:
According to Henry’s law, the solubility of a gas in a liquid increases with an increase in pressure. Conversely, increasing temperature generally decreases gas solubility.
29. In the reaction A(g)+2B(g)⇌C(g)A(g)+2B(g)⇌C(g), what happens to the position of equilibrium if the total pressure is increased?
a) Shifts to the left
b) Shifts to the right
c) No change
d) Cannot predict without KcKc
Answer: b) Shifts to the right
Explanation:
Increasing pressure favors the side of the reaction with fewer gas molecules. On the right side, there is 1 mole of gas, while on the left side, there are 3 moles of gas. So the equilibrium shifts to the right.
30. Which of the following statements is correct for a solution of a weak base and its salt?
a) The pH is less than 7
b) The pH is more than 7
c) The pH is equal to 7
d) The pH is independent of concentration
Answer: b) The pH is more than 7
Explanation:
A buffer solution containing a weak base and its salt has a pH greater than 7 because the weak base produces OH−− ions, making the solution basic.
Leave a comment