1. Which of the following is true for a system in chemical equilibrium?
a) The concentrations of reactants and products become equal.
b) The rate of the forward reaction is equal to the rate of the reverse reaction.
c) The forward reaction stops completely.
d) The system is no longer dynamic.
Answer: b) The rate of the forward reaction is equal to the rate of the reverse reaction.
Explanation:
At equilibrium, the forward and reverse reaction rates are equal, meaning that the concentrations of reactants and products remain constant over time, not necessarily equal. The reaction continues to occur in both directions, maintaining a dynamic state.
2. In a reversible reaction at equilibrium, which of the following will NOT change the position of equilibrium?
a) Change in temperature
b) Change in pressure
c) Addition of a catalyst
d) Change in concentration of reactants
Answer: c) Addition of a catalyst
Explanation:
A catalyst speeds up both the forward and reverse reactions equally without affecting the equilibrium position. It only helps the system reach equilibrium faster but does not shift the position of equilibrium.
3. The equilibrium constant KcKc for a reaction is 10. If the reaction is reversed, what will be the new equilibrium constant?
a) 0.1
b) 1
c) 100
d) 10
Answer: a) 0.1
Explanation:
For the reverse of a reaction, the equilibrium constant becomes the reciprocal of the original KcKc. So, if Kc=10Kc=10, the reverse reaction will have Kc=110=0.1Kc=101=0.1.
4. In the reaction H2(g)+I2(g)⇌2HI(g)H2(g)+I2(g)⇌2HI(g), if some HI is removed from the system, what will happen according to Le Chatelier’s principle?
a) More HI will be formed.
b) More H22 and I22 will be formed.
c) The equilibrium constant will change.
d) The system will remain unchanged.
Answer: a) More HI will be formed.
Explanation:
According to Le Chatelier’s principle, if HI is removed, the system will shift to the right to replace the removed HI by producing more of it, thus counteracting the disturbance.
5. In which of the following solutions will the degree of dissociation of a weak acid be highest?
a) 0.01 M solution of the acid
b) 0.1 M solution of the acid
c) 1 M solution of the acid
d) 10 M solution of the acid
Answer: a) 0.01 M solution of the acid
Explanation:
The degree of dissociation (αα) of a weak acid is inversely proportional to the concentration of the acid. Lower concentrations have higher degrees of dissociation, so 0.01 M solution will have the highest dissociation.
6. Which of the following will increase the dissociation of acetic acid in an aqueous solution?
a) Adding HCl
b) Adding CH33COONa
c) Adding NaOH
d) Increasing the pressure
Answer: c) Adding NaOH
Explanation:
NaOH reacts with the H++ ions produced by acetic acid, removing them from the solution. This shifts the equilibrium towards more dissociation of acetic acid to replace the removed H++ ions, thereby increasing dissociation.
7. For a given weak electrolyte, which of the following factors increases its degree of ionization?
a) Decreasing the dilution
b) Increasing the dilution
c) Adding a common ion
d) Increasing temperature for an exothermic dissociation reaction
Answer: b) Increasing the dilution
Explanation:
The degree of ionization of a weak electrolyte increases with dilution according to Ostwald’s dilution law. As dilution increases, the concentration of ions increases relative to the undissociated molecules.
8. Which of the following will decrease the pH of a buffer solution containing a weak acid and its salt?
a) Adding more of the weak acid
b) Adding more of the salt
c) Adding water
d) Adding NaOH
Answer: a) Adding more of the weak acid
Explanation:
Adding more weak acid increases the concentration of H++ ions, thus lowering the pH of the buffer solution.
9. The ionization constant (KbKb) of a weak base B is 2 × 10−5−5. What is the nature of the base?
a) Strong base
b) Weak base
c) Neutral
d) Amphoteric
Answer: b) Weak base
Explanation:
A base with a low KbKb value (typically less than 10−2−2) is considered a weak base, as it does not completely dissociate in water.
10. What happens to the ionic product of water (KwKw) as temperature increases?
a) It decreases
b) It remains constant
c) It increases
d) It first decreases, then increases
Answer: c) It increases
Explanation:
The dissociation of water into H++ and OH−− ions is an endothermic process, so according to Le Chatelier’s principle, an increase in temperature favors the dissociation, increasing KwKw.
Leave a comment