Free Chemical Equilibrium MCQs with Answers
625 Chemical Equilibrium MCQs from Chemistry, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.
Reversible reactions reach dynamic equilibrium when forward and reverse rates become equal, and Le Chatelier's principle predicts the effect of changing concentration, pressure or temperature. The chapter also covers solubility product, the common ion effect, buffer action and the conditions used in Haber's process, with equilibrium shifts distinguished from changes in the equilibrium constant.
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- A. both reactions have stopped completely
- B. the forward and reverse reactions continue at equal rates
- C. the amounts of reactants and products are equal
- D. all the reactants have been converted to products
Explanation: The word dynamic means both reactions are still running; they simply cancel out, so the concentrations stay constant while molecules…
Correct answer: the forward and reverse reactions continue at equal rates- A. [N2][H2]^3 divided by [NH3]^2
- B. [NH3] divided by [N2][H2]
- C. [NH3]^2 divided by [N2][H2]^3
- D. 2[NH3] divided by [N2] + 3[H2]
Explanation: Kc is written as the product concentrations over the reactant concentrations, each raised to the power of its coefficient in the balanced…
Correct answer: [NH3]^2 divided by [N2][H2]^3- A. the reaction reaches equilibrium very quickly
- B. the reaction is exothermic
- C. the reactants are favoured at equilibrium
- D. the products are strongly favoured at equilibrium
Explanation: Kc compares product to reactant concentrations, so a large value means the equilibrium position lies far to the right and the reaction…
Correct answer: the products are strongly favoured at equilibrium4. Le Chatelier's principle states that when a stress is applied to a system at equilibrium, the system
- A. shifts in the direction that relieves the stress
- B. shifts in the direction that increases the stress
- C. stops reacting altogether
- D. always shifts towards the products
Explanation: The position of equilibrium moves so as to partly oppose the change imposed, whether that change is in concentration, pressure or…
Correct answer: shifts in the direction that relieves the stress5. For the equilibrium N2 + 3H2 gives 2NH3, which is exothermic, the yield of ammonia is increased by
- A. raising the temperature and lowering the pressure
- B. raising the pressure and lowering the temperature
- C. adding a catalyst
- D. removing nitrogen from the mixture
Explanation: There are four moles of gas on the left and two on the right, so high pressure pushes the equilibrium towards the smaller volume, and…
Correct answer: raising the pressure and lowering the temperature6. Increasing the pressure has NO effect on the position of the equilibrium H2 + I2 gives 2HI because
- A. the reaction is exothermic
- B. hydrogen iodide is a gas
- C. the number of moles of gas is the same on both sides
- D. the reaction has no catalyst
Explanation: Pressure changes shift an equilibrium only when the two sides differ in the number of gas molecules, and here there are two moles on each…
Correct answer: the number of moles of gas is the same on both sides- A. shifts the equilibrium towards the products
- B. shifts the equilibrium towards the reactants
- C. increases the value of Kc
- D. speeds up the forward and reverse reactions equally, so equilibrium is reached sooner but is unchanged
Explanation: A catalyst lowers the activation energy of both directions by the same amount, so both rates rise in proportion and they still become…
Correct answer: speeds up the forward and reverse reactions equally, so equilibrium is reached sooner but is unchanged- A. finely divided iron with promoters
- B. platinum
- C. vanadium pentoxide
- D. nickel
Explanation: Iron with small amounts of potassium and aluminium oxide as promoters is used because it is effective and cheap enough for a process…
Correct answer: finely divided iron with promoters- A. 1000 degrees Celsius and 1 atmosphere
- B. 25 degrees Celsius and 1000 atmospheres
- C. 450 degrees Celsius and 200 atmospheres
- D. 450 degrees Celsius and 1 atmosphere
Explanation: A moderately high temperature is a compromise, since a low temperature would give a better yield but far too slowly for industry, while…
Correct answer: 450 degrees Celsius and 200 atmospheres- A. the total mass of the salt dissolved
- B. the product of the concentrations of its ions in a saturated solution, each raised to the power of its coefficient
- C. the concentration of the undissolved solid
- D. the ratio of dissolved to undissolved salt
Explanation: For a saturated solution in contact with excess solid, an equilibrium exists between the solid and its ions, and Ksp is the equilibrium…
Correct answer: the product of the concentrations of its ions in a saturated solution, each raised to the power of its coefficient- A. Ksp = [Ag+] + [Cl-]
- B. Ksp = [AgCl] divided by [Ag+][Cl-]
- C. Ksp = [Ag+][Cl-] divided by [AgCl]
- D. Ksp = [Ag+][Cl-]
Explanation: Silver chloride dissociates into one silver ion and one chloride ion, so Ksp is simply the product of the two concentrations, and the…
Correct answer: Ksp = [Ag+][Cl-]- A. the common ion effect
- B. the buffer action
- C. hydrolysis
- D. the catalytic effect
Explanation: Sodium chloride supplies extra chloride ions, and since the ionic product must not exceed Ksp the equilibrium shifts towards the…
Correct answer: the common ion effect- A. sodium acetate is a strong acid
- B. the added acetate ions shift the ionisation equilibrium back towards the un-ionised acid
- C. sodium ions react with the acid
- D. the temperature of the solution falls
Explanation: Sodium acetate is fully ionised and floods the solution with acetate, the common ion, so by Le Chatelier's principle the acid dissociates…
Correct answer: the added acetate ions shift the ionisation equilibrium back towards the un-ionised acid- A. has a pH of exactly 7
- B. neutralises all acids completely
- C. resists a change in pH when a small amount of acid or base is added
- D. conducts electricity better than water
Explanation: A buffer contains a reservoir of both a weak acid and its conjugate base, so added hydrogen ions are mopped up by the base and added…
Correct answer: resists a change in pH when a small amount of acid or base is added- A. Hydrochloric acid and sodium chloride
- B. Sodium hydroxide and sodium chloride
- C. Ammonia and ammonium chloride
- D. Acetic acid and sodium acetate
Explanation: An acidic buffer needs a weak acid together with the salt of that acid, and acetic acid with sodium acetate is the standard example.
Correct answer: Acetic acid and sodium acetate- A. concentration of the reactants
- B. pressure of the system
- C. temperature
- D. the catalyst used
Explanation: Concentration and pressure changes shift the position of equilibrium so that the same value of Kc is restored, and a catalyst affects only…
Correct answer: temperature- A. shift the equilibrium towards the products and increase Kc
- B. shift the equilibrium towards the reactants
- C. have no effect
- D. decrease the rate of both reactions
Explanation: Heat can be treated as a reactant in an endothermic reaction, so supplying more of it drives the system forward to absorb the extra…
Correct answer: shift the equilibrium towards the products and increase Kc- A. no more solid can be added to the container
- B. the dissolved ions are in equilibrium with the undissolved solid
- C. the salt has completely dissolved
- D. the solubility product has been exceeded
Explanation: In a saturated solution ions leave the solid surface and return to it at the same rate, so the concentration of dissolved ions stays…
Correct answer: the dissolved ions are in equilibrium with the undissolved solid- A. decrease the amount of C formed
- B. have no effect on the position of equilibrium
- C. shift the equilibrium to the right, forming more C and D
- D. change the value of Kc
Explanation: The system responds to the extra A by consuming some of it, which means running the forward reaction further and producing more products…
Correct answer: shift the equilibrium to the right, forming more C and D- A. the total volume of the solution
- B. the temperature only
- C. the presence of a catalyst
- D. the dissociation constant of the acid and the ratio of salt to acid concentration
Explanation: The Henderson Hasselbalch relationship gives pH as pKa plus the logarithm of the ratio of salt to acid, so it is the ratio that matters…
Correct answer: the dissociation constant of the acid and the ratio of salt to acid concentrationChemical Equilibrium MCQs: common questions
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