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.
11. Which of the following is true about the equilibrium constant (KcKc) for a reaction?
a) It depends on the concentration of reactants and products.
b) It changes with temperature.
c) It changes with pressure.
d) It depends on the initial concentration of reactants.
Answer: b) It changes with temperature.
Explanation:
The equilibrium constant depends only on temperature, not on the concentrations of reactants or products, or pressure. A change in temperature can shift the equilibrium, changing the KcKc.
12. In the dissociation of ammonia in water, NH3+H2O⇌NH4++OH−NH3+H2O⇌NH4++OH−, what is the effect of adding an acid?
a) The concentration of OH−OH− increases.
b) The concentration of OH−OH− decreases.
c) The dissociation of ammonia increases.
d) The dissociation of ammonia decreases.
Answer: b) The concentration of OH−OH− decreases.
Explanation:
Adding an acid increases the concentration of H++ ions, which react with OH−− ions to form water, thereby decreasing the concentration of OH−−.
13. Which of the following conditions will favor the forward reaction in an exothermic equilibrium reaction?
a) Increasing the temperature
b) Decreasing the temperature
c) Increasing the concentration of products
d) Adding a catalyst
Answer: b) Decreasing the temperature
Explanation:
In an exothermic reaction, decreasing the temperature favors the forward reaction, as the system will shift to produce more heat, which is in line with Le Chatelier’s principle.
14. Which of the following statements is correct for a solution of a weak electrolyte?
a) The ionization increases with increasing concentration.
b) The ionization decreases with increasing concentration.
c) The ionization is unaffected by dilution.
d) The ionization is complete at all concentrations.
Answer: b) The ionization decreases with increasing concentration.
Explanation:
According to Ostwald’s dilution law, the degree of ionization of a weak electrolyte decreases as the concentration increases.
15. Which of the following salts will produce a basic solution in water?
a) NaCl
b) KNO33
c) CH33COONa
d) NH44Cl
Answer: c) CH33COONa
Explanation:
CH33COONa is a salt of a weak acid (acetic acid) and a strong base (sodium hydroxide). When dissolved in water, it hydrolyzes to form OH−− ions, making the solution basic.
16. In a buffer solution containing a weak acid and its conjugate base, the pH will:
a) Decrease when more conjugate base is added
b) Increase when more conjugate base is added
c) Remain unchanged when acid is added
d) Remain unchanged when base is added
Answer: b) Increase when more conjugate base is added
Explanation:
Adding more conjugate base increases the concentration of the base relative to the acid, which reduces the concentration of H++ ions, raising the pH.
17. For the dissociation of acetic acid, which of the following factors will increase the equilibrium concentration of CH3COO−CH3COO−?
a) Addition of NaOH
b) Addition of HCl
c) Increasing the temperature
d) Decreasing the concentration of acetic acid
Answer: a) Addition of NaOH
Explanation:
NaOH reacts with H++ ions, which decreases the H++ concentration. This causes the equilibrium to shift to the right to replace the lost H++, increasing the concentration of CH3COO−CH3COO−.
18. In the equilibrium N2O4(g)⇌2NO2(g)N2O4(g)⇌2NO2(g), what will happen if the volume of the system is increased?
a) The equilibrium will shift towards the products.
b) The equilibrium will shift towards the reactants.
c) The equilibrium constant will increase.
d) The equilibrium will not shift.
Answer: a) The equilibrium will shift towards the products.
Explanation:
According to Le Chatelier’s principle, increasing the volume (decreasing pressure) shifts the equilibrium towards the side with more gas molecules. In this case, there are more moles of gas on the product side (2 NO22).
19. The solubility of AgCl in water will increase if:
a) NaCl is added to the solution
b) HCl is added to the solution
c) Ammonia is added to the solution
d) The temperature is decreased
Answer: c) Ammonia is added to the solution
Explanation:
Ammonia reacts with Ag++ ions to form a complex ion [Ag(NH3)2]+[Ag(NH3)2]+, which reduces the concentration of Ag++ in solution, thus increasing the solubility of AgCl.
20. Which of the following is an example of a buffer solution?
a) HCl and NaCl
b) NaOH and NaCl
c) NH44OH and NH44Cl
d) HNO33 and NaNO33
Answer: c) NH44OH and NH44Cl
Explanation:
A buffer solution contains a weak acid and its conjugate base or a weak base and its conjugate acid. NH44OH (weak base) and NH44Cl (its conjugate acid) form a buffer solution.
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.
31. If KcKc for a reaction is very small (much less than 1), what can be inferred about the equilibrium position?
a) The reaction favors the products.
b) The reaction favors the reactants.
c) The reaction reaches equilibrium very quickly.
d) The reaction does not proceed at all.
Answer: b) The reaction favors the reactants.
Explanation:
A small KcKc value means that the concentration of reactants at equilibrium is much higher than the concentration of products, so the reaction favors the reactants.
32. What will be the effect of adding NaCl to a solution of AgNO33?
a) No effect
b) Decrease in the concentration of Ag++ ions
c) Increase in the concentration of Ag++ ions
d) Decrease in the concentration of Cl−− ions
Answer: b) Decrease in the concentration of Ag++ ions
Explanation:
Adding NaCl provides Cl−− ions, which react with Ag++ ions to form a precipitate of AgCl, decreasing the concentration of free Ag++ ions in solution.
33. Which of the following statements is true about a buffer solution?
a) It resists changes in pH when small amounts of acid or base are added.
b) It can be made only with a strong acid and its salt.
c) It becomes more effective as the pH is lowered.
d) Its pH changes drastically upon dilution.
Answer: a) It resists changes in pH when small amounts of acid or base are added.
Explanation:
A buffer solution maintains a nearly constant pH by neutralizing small amounts of added acid or base.
34. For the reaction 2SO2(g)+O2(g)⇌2SO3(g)2SO2(g)+O2(g)⇌2SO3(g), which of the following will decrease the amount of SO33?
a) Decreasing the pressure
b) Increasing the concentration of SO22
c) Increasing the pressure
d) Adding a catalyst
Answer: a) Decreasing the pressure
Explanation:
Since the forward reaction results in fewer moles of gas (from 3 moles to 2 moles), decreasing the pressure will shift the equilibrium to the left, reducing the amount of SO33.
35. What is the effect of adding NH44Cl to a solution of NH33?
a) The ionization of NH33 decreases.
b) The ionization of NH33 increases.
c) The pH of the solution increases.
d) The concentration of OH−− increases.
Answer: a) The ionization of NH33 decreases.
Explanation:
NH44Cl provides NH4+4+ ions, which shift the equilibrium of the dissociation of NH33 (a weak base) to the left, reducing its ionization (common ion effect).
36. Which of the following is a characteristic of a system in equilibrium?
a) The forward reaction has stopped.
b) The reverse reaction has stopped.
c) The concentrations of reactants and products remain constant over time.
d) The equilibrium constant changes with concentration.
Answer: c) The concentrations of reactants and products remain constant over time.
Explanation:
In equilibrium, the rates of the forward and reverse reactions are equal, so the concentrations of reactants and products do not change over time.
37. Which of the following statements is correct about the solubility product (KspKsp)?
a) It depends on the concentration of the solid phase.
b) It increases with the addition of a common ion.
c) It decreases with the increase in temperature for most salts.
d) It is constant at a given temperature.
Answer: d) It is constant at a given temperature.
Explanation:
The solubility product (KspKsp) is a constant for a given solute at a specific temperature. It depends only on temperature and not on the concentration of the solid phase or the addition of common ions.
38. In an acidic solution, which of the following species will increase in concentration when more acid is added?
a) OH−−
b) H++
c) Water molecules
d) Conjugate base
Answer: b) H++
Explanation:
Adding more acid increases the concentration of H++ ions (protons) in the solution, making it more acidic.
39. The equilibrium constant for a reaction is 50 at 500 K. If the temperature is raised to 600 K, what will likely happen to the equilibrium constant if the reaction is exothermic?
a) It will increase.
b) It will decrease.
c) It will remain the same.
d) It will first increase, then decrease.
Answer: b) It will decrease.
Explanation:
For an exothermic reaction, increasing the temperature shifts the equilibrium to the left, decreasing the value of the equilibrium constant.
40. The addition of a catalyst to a system at equilibrium will:
a) Shift the equilibrium to the right.
b) Shift the equilibrium to the left.
c) Decrease the equilibrium constant.
d) Increase the rate at which equilibrium is achieved.
Answer: d) Increase the rate at which equilibrium is achieved.
Explanation:
A catalyst increases the rate of both the forward and reverse reactions equally, allowing the system to reach equilibrium faster without changing the position of equilibrium or the equilibrium constant.
41. In the reaction H2(g)+Cl2(g)⇌2HCl(g)H2(g)+Cl2(g)⇌2HCl(g), the equilibrium constant KcKc is 100 at a given temperature. What will be the equilibrium constant for the reverse reaction?
a) 1
b) 10
c) 0.01
d) 0.1
Answer: c) 0.01
Explanation:
For the reverse reaction, the equilibrium constant is the reciprocal of the forward reaction’s KcKc. Thus, Kc(reverse)=1100=0.01Kc(reverse)=1001=0.01.
42. For the dissociation reaction of PCl5(g)⇌PCl3(g)+Cl2(g)PCl5(g)⇌PCl3(g)+Cl2(g), increasing the concentration of Cl2Cl2 will:
a) Shift the equilibrium to the right
b) Shift the equilibrium to the left
c) Increase the concentration of PCl5PCl5
d) Both b and c
Answer: d) Both b and c
Explanation:
Increasing the concentration of Cl2Cl2 will shift the equilibrium to the left (towards PCl5PCl5) according to Le Chatelier’s principle, thereby increasing the concentration of PCl5PCl5.
43. Which of the following changes will NOT affect the position of equilibrium in the reaction H2(g)+I2(g)⇌2HI(g)H2(g)+I2(g)⇌2HI(g)?
a) Increasing the pressure
b) Adding more H2H2
c) Decreasing the temperature
d) Adding a catalyst
Answer: d) Adding a catalyst
Explanation:
A catalyst speeds up the forward and reverse reactions equally but does not affect the position of equilibrium or the equilibrium constant.
44. For the reaction N2(g)+3H2(g)⇌2NH3(g)N2(g)+3H2(g)⇌2NH3(g), what will happen if the volume of the container is decreased?
a) The equilibrium will shift to the right.
b) The equilibrium will shift to the left.
c) The equilibrium will remain unchanged.
d) The value of KcKc will increase.
Answer: a) The equilibrium will shift to the right.
Explanation:
Decreasing the volume increases the pressure. Since there are fewer moles of gas on the right side (2 moles of NH3NH3) compared to the left side (4 moles of N2+H2N2+H2), the equilibrium shifts to the side with fewer moles of gas.
45. The dissociation constant (KaKa) of acetic acid is 1.8×10−51.8×10−5. Which of the following is the correct expression for the pH of a 0.1 M solution of acetic acid?
a) pH = 7
b) pH = 1
c) pH = 5
d) pH = 2.9
Answer: d) pH = 2.9
Explanation:
Using the formula for a weak acid, [H+]=Ka⋅[HA][H+]=Ka⋅[HA], we calculate the concentration of H+H+ and then find the pH. For acetic acid, pH≈2.9pH≈2.9.
46. Which of the following is an example of a Lewis acid?
a) OH−OH−
b) NH3NH3
c) BF3BF3
d) H2OH2O
Answer: c) BF3BF3
Explanation:
A Lewis acid is an electron pair acceptor. BF3BF3 lacks a complete octet on the boron atom and can accept electron pairs, making it a Lewis acid.
47. In the equilibrium CO2(g)+H2O(l)⇌H2CO3(aq)CO2(g)+H2O(l)⇌H2CO3(aq), what will be the effect of increasing the pressure?
a) The equilibrium shifts to the left.
b) The equilibrium shifts to the right.
c) The value of KcKc increases.
d) The equilibrium constant decreases.
Answer: b) The equilibrium shifts to the right.
Explanation:
Increasing the pressure will shift the equilibrium to the side with fewer gas molecules. Since there is only one gas molecule on the left and no gas on the right, the equilibrium shifts to the right.
48. For the dissociation of water, H2O(l)⇌H+(aq)+OH−(aq)H2O(l)⇌H+(aq)+OH−(aq), at 298 K, the value of KwKw is 1×10−141×10−14. What is the pH of pure water?
a) 7
b) 14
c) 1
d) 5
Answer: a) 7
Explanation:
For pure water, [H+]=[OH−]=Kw=1×10−7[H+]=[OH−]=Kw=1×10−7. Therefore, the pH is −log[H+]=7−log[H+]=7, which is neutral at 298 K.
49. Which of the following will increase the degree of dissociation of a weak acid in water?
a) Adding a common ion
b) Increasing the concentration of the acid
c) Diluting the solution
d) Adding a strong acid
Answer: c) Diluting the solution
Explanation:
According to Ostwald’s dilution law, the degree of dissociation of a weak acid increases as the solution is diluted.
50. The value of KcKc for the reaction H2(g)+I2(g)⇌2HI(g)H2(g)+I2(g)⇌2HI(g) is 50. What is the equilibrium concentration of HIHI if the concentrations of H2H2 and I2I2 are both 0.1 M?
a) 0.5 M
b) 0.1 M
c) 0.7 M
d) 0.05 M
Answer: a) 0.5 M
Explanation:
Using the expression for KcKc, Kc=[HI]2[H2][I2]Kc=[H2][I2][HI]2, and solving for [HI][HI], the equilibrium concentration of HI is found to be 0.5 M.
51. Which of the following solutions will have a pH greater than 7?
a) NaCl
b) NH44Cl
c) Na22CO33
d) HCl
Answer: c) Na22CO33
Explanation:
Na22CO33 is a salt of a strong base (NaOH) and a weak acid (H22CO33). It undergoes hydrolysis in water to produce OH−− ions, making the solution basic with a pH greater than 7.
52. Which of the following will have the highest solubility in an acidic solution?
a) Mg(OH)22
b) AgCl
c) NaCl
d) CaCO33
Answer: a) Mg(OH)22
Explanation:
Magnesium hydroxide is a sparingly soluble base. In an acidic solution, the H++ ions react with OH−−, increasing the solubility of Mg(OH)22.
Leave a comment