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1. A state in which the concentrations of reactants and products remain constant over time in a reversible reaction is called:
A. Chemical equilibrium
B. Complete reaction
C. Irreversible reaction
D. Catalytic reaction
Answer: A. Chemical equilibrium
Explanation: Chemical equilibrium is reached when the rates of the forward and reverse reactions become equal, resulting in constant concentrations.
2. At chemical equilibrium, the rate of the forward reaction is:
A. Equal to the rate of the reverse reaction
B. Greater than the reverse reaction
C. Less than the reverse reaction
D. Zero
Answer: A. Equal to the rate of the reverse reaction
Explanation: The defining characteristic of equilibrium is that the forward and reverse reaction rates become exactly equal, though both continue to occur.
3. The equilibrium constant (Kc) is expressed in terms of the:
A. Molar concentrations of reactants and products
B. Only the concentration of reactants
C. Only the concentration of products
D. Temperature alone
Answer: A. Molar concentrations of reactants and products
Explanation: Kc is calculated using the equilibrium molar concentrations of both the products and reactants, raised to their respective stoichiometric powers.
4. The equilibrium constant expressed in terms of partial pressures of gases is denoted as:
A. Kp
B. Kc
C. Ka
D. Kb
Answer: A. Kp
Explanation: Kp specifically uses the partial pressures of gaseous reactants and products to express the equilibrium constant.
5. A large value of the equilibrium constant (K) generally indicates that the equilibrium favours the formation of:
A. Products
B. Reactants
C. Neither reactants nor products
D. Only intermediate species
Answer: A. Products
Explanation: A large K value implies that at equilibrium, the concentration of products significantly exceeds that of the reactants.
6. Le Chatelier's Principle states that if a system at equilibrium is subjected to a change, the system will adjust to:
A. Counteract the applied change and restore a new equilibrium
B. Completely reverse the reaction
C. Stop the reaction entirely
D. Ignore the change
Answer: A. Counteract the applied change and restore a new equilibrium
Explanation: Le Chatelier's Principle predicts that an equilibrium system responds to external stress by shifting in a direction that minimises the effect of that change.
7. According to Le Chatelier's Principle, increasing the concentration of a reactant will shift the equilibrium towards the:
A. Products (forward direction)
B. Reactants (reverse direction)
C. No change at all
D. Complete reaction stoppage
Answer: A. Products (forward direction)
Explanation: Adding more reactant increases the forward reaction rate, shifting the equilibrium position towards greater product formation.
8. According to Le Chatelier's Principle, increasing pressure on a gaseous equilibrium system will shift the equilibrium towards the side with:
A. Fewer moles of gas
B. More moles of gas
C. Equal moles on each side
D. No gaseous species at all
Answer: A. Fewer moles of gas
Explanation: Increased pressure favours the side of the reaction with fewer gas molecules, as this reduces the overall volume and counteracts the pressure increase.
9. According to Le Chatelier's Principle, for an exothermic reaction, increasing the temperature will shift the equilibrium towards the:
A. Reactants (reverse direction)
B. Products (forward direction)
C. No specific direction
D. Complete reaction stoppage
Answer: A. Reactants (reverse direction)
Explanation: Since heat is treated as a product in an exothermic reaction, increasing temperature shifts the equilibrium backward, favouring the reactants.
10. According to Arrhenius theory, an acid is a substance that, when dissolved in water, produces:
A. Hydrogen ions (H⁺)
B. Hydroxide ions (OH⁻)
C. Only neutral molecules
D. Only metal ions
Answer: A. Hydrogen ions (H⁺)
Explanation: Arrhenius defined an acid specifically as a substance that increases the concentration of hydrogen ions when dissolved in aqueous solution.
11. According to Arrhenius theory, a base is a substance that, when dissolved in water, produces:
A. Hydroxide ions (OH⁻)
B. Hydrogen ions (H⁺)
C. Only neutral molecules
D. Only non-metal ions
Answer: A. Hydroxide ions (OH⁻)
Explanation: Arrhenius defined a base as a substance that increases the concentration of hydroxide ions upon dissolving in water.
12. According to the Brønsted-Lowry theory, an acid is defined as a substance that:
A. Donates a proton (H⁺)
B. Accepts a proton
C. Donates an electron pair
D. Accepts an electron pair
Answer: A. Donates a proton (H⁺)
Explanation: The Brønsted-Lowry theory broadens the definition of an acid to any species capable of donating a proton to another substance.
13. According to the Brønsted-Lowry theory, a base is defined as a substance that:
A. Accepts a proton (H⁺)
B. Donates a proton
C. Accepts an electron pair only
D. Donates an electron pair only
Answer: A. Accepts a proton (H⁺)
Explanation: The Brønsted-Lowry theory defines a base as any species capable of accepting a proton from an acid.
14. According to the Lewis theory, an acid is defined as a substance that:
A. Accepts a pair of electrons
B. Donates a pair of electrons
C. Donates a proton only
D. Accepts a proton only
Answer: A. Accepts a pair of electrons
Explanation: Lewis theory offers the broadest definition, describing an acid as any species capable of accepting an electron pair.
15. According to the Lewis theory, a base is defined as a substance that:
A. Donates a pair of electrons
B. Accepts a pair of electrons
C. Donates a proton only
D. Accepts a proton only
Answer: A. Donates a pair of electrons
Explanation: A Lewis base is defined as a species that donates an electron pair to form a coordinate bond with a Lewis acid.
16. The pH scale is used to measure the:
A. Acidity or basicity of a solution
B. Temperature of a solution
C. Concentration of dissolved oxygen
D. Colour of a solution
Answer: A. Acidity or basicity of a solution
Explanation: The pH scale quantitatively expresses the concentration of hydrogen ions, indicating whether a solution is acidic, neutral or basic.
17. A solution with a pH value of 7 is considered:
A. Neutral
B. Acidic
C. Basic
D. Highly acidic
Answer: A. Neutral
Explanation: A pH of exactly 7 indicates a neutral solution, where the concentrations of hydrogen and hydroxide ions are equal, as in pure water.
18. A solution with a pH value less than 7 is considered:
A. Acidic
B. Basic
C. Neutral
D. Undefined
Answer: A. Acidic
Explanation: Solutions with a pH below 7 have a higher concentration of hydrogen ions, classifying them as acidic.
19. A solution with a pH value greater than 7 is considered:
A. Basic
B. Acidic
C. Neutral
D. Undefined
Answer: A. Basic
Explanation: Solutions with a pH above 7 have a higher concentration of hydroxide ions relative to hydrogen ions, classifying them as basic.
20. The formula relating pH to hydrogen ion concentration is:
A. pH = -log[H⁺]
B. pH = log[H⁺]
C. pH = [H⁺]
D. pH = 1/[H⁺]
Answer: A. pH = -log[H⁺]
Explanation: pH is mathematically defined as the negative logarithm (base 10) of the hydrogen ion concentration in a solution.
21. A buffer solution is one that resists changes in:
A. pH upon the addition of small amounts of acid or base
B. Colour upon heating
C. Volume upon stirring
D. Temperature upon cooling
Answer: A. pH upon the addition of small amounts of acid or base
Explanation: Buffer solutions are specifically designed to maintain a relatively stable pH even when small amounts of acid or base are added.
22. A buffer solution is typically prepared using a mixture of:
A. A weak acid and its conjugate base (or a weak base and its conjugate acid)
B. Two strong acids
C. Two strong bases
D. Only pure water
Answer: A. A weak acid and its conjugate base (or a weak base and its conjugate acid)
Explanation: Effective buffers rely on the equilibrium between a weak acid/base and its corresponding conjugate species to resist pH changes.
23. The equilibrium constant for the ionisation of water (Kw) at 25°C has a value of approximately:
A. 1 × 10⁻¹⁴
B. 1 × 10⁻⁷
C. 1 × 10⁷
D. 1 × 10¹⁴
Answer: A. 1 × 10⁻¹⁴
Explanation: The ion product of water, Kw, has a standard value of approximately 1 × 10⁻¹⁴ at 25°C.
24. According to the common ion effect, adding a common ion to a solution at equilibrium generally causes the equilibrium to shift in a direction that:
A. Reduces the concentration of the added common ion
B. Increases the concentration of the added ion further
C. Has no effect on the equilibrium
D. Completely reverses the reaction
Answer: A. Reduces the concentration of the added common ion
Explanation: The common ion effect describes how adding an ion already present in the equilibrium mixture shifts the equilibrium to counteract that increase, consistent with Le Chatelier's Principle.
25. Salts formed from the reaction of a strong acid and a strong base typically produce solutions that are:
A. Neutral
B. Strongly acidic
C. Strongly basic
D. Highly reactive
Answer: A. Neutral
Explanation: Since neither ion undergoes significant hydrolysis, salts of strong acids and strong bases generally form neutral aqueous solutions.
26. The solubility product (Ksp) is used to describe the equilibrium of:
A. A sparingly soluble salt with its dissolved ions in solution
B. A gas dissolving in a liquid only
C. Two immiscible liquids
D. A pure solid melting
Answer: A. A sparingly soluble salt with its dissolved ions in solution
Explanation: The solubility product constant specifically applies to the equilibrium between an undissolved sparingly soluble solid and its constituent ions in a saturated solution.
27. Increasing the temperature generally affects the value of the equilibrium constant (K) for a reaction because K is:
A. Temperature-dependent
B. Always constant regardless of temperature
C. Independent of the reaction type
D. Only relevant for gaseous reactions
Answer: A. Temperature-dependent
Explanation: Unlike changes in concentration or pressure, a change in temperature actually alters the numerical value of the equilibrium constant itself.
28. For a reaction at equilibrium, adding an inert gas at constant volume will:
A. Not shift the equilibrium position
B. Always shift equilibrium towards products
C. Always shift equilibrium towards reactants
D. Completely stop the reaction
Answer: A. Not shift the equilibrium position
Explanation: Adding an inert gas at constant volume does not change the partial pressures or concentrations of the reacting species, so the equilibrium position remains unaffected.
29. The reaction quotient (Q) is compared with the equilibrium constant (K) to determine:
A. The direction in which a reaction will proceed to reach equilibrium
B. The exact temperature of the reaction
C. The colour change of the reaction
D. The physical state of reactants
Answer: A. The direction in which a reaction will proceed to reach equilibrium
Explanation: By comparing Q to K, chemists can predict whether a reaction will proceed forward, backward, or is already at equilibrium.
30. According to Ostwald's dilution law, the degree of ionisation of a weak electrolyte generally increases with:
A. Increasing dilution
B. Increasing concentration
C. Decreasing temperature only
D. Adding a common ion
Answer: A. Increasing dilution
Explanation: Ostwald's dilution law shows that as a weak electrolyte solution becomes more dilute, its degree of ionisation increases.
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