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GCE A-Level (Singapore) Fundamental Equilibrium Concepts — practice questions

Explore 33 free Fundamental Equilibrium Concepts questions in GCE A-Level (Singapore) Chemistry. Open each question or exercise to read its content, reference answers and available explanation.

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Fundamental Equilibrium Concepts questions and exercises with answers

Showing questions 1–30 of 33.

In a chemical equilibrium, what is true of the forward and the reverse reaction?Read the answer and worked solution →A reversible reaction run in a closed system usually gives what yield of products?Read the answer and worked solution →Liquid bromine is poured into a bottle. What condition lets a liquid to vapour equilibrium form?Read the answer and worked solution →Pure reactants alone are mixed in a flask. What is the value of Qc at that instant?Read the answer and worked solution →For 2NO2 forming N2O4, equilibrium gives [NO2] = 0.016 M and [N2O4] = 0.042 M. What is Kc?Read the answer and worked solution →A mixture has Qc smaller than Kc. In which direction will the reaction proceed?Read the answer and worked solution →What defines a homogeneous equilibrium?Read the answer and worked solution →Water appears as a product in a gas phase reaction. Does its concentration enter the Kc expression?Read the answer and worked solution →For N2(g) + 3H2(g) forming 2NH3(g), how does Kp relate to Kc?Read the answer and worked solution →For CS2(g) + 4H2(g) forming CH4(g) + 2H2S(g), Kc = 0.28 at 900 degrees Celsius. What is Kp?Read the answer and worked solution →For which kind of gaseous reaction does Kp come out numerically equal to Kc?Read the answer and worked solution →What makes an equilibrium heterogeneous?Read the answer and worked solution →For CaO(s) + CO2(g) forming CaCO3(s), what is the equilibrium constant expression Kc?Read the answer and worked solution →Solid lead(II) chloride dissolves as PbCl2(s) forming Pb2+(aq) and 2Cl-(aq). What is Kc?Read the answer and worked solution →Liquid bromine evaporates as Br2(l) forming Br2(g). What is the Kc expression for this change?Read the answer and worked solution →At equilibrium for 2SO2 + O2 forming 2SO3, [SO2] = 0.90 M, [O2] = 0.35 M and [SO3] = 1.1 M. What is Kc?Read the answer and worked solution →State the principle that predicts how a disturbed equilibrium responds.Read the answer and worked solution →How can a system at equilibrium be temporarily pushed out of equilibrium?Read the answer and worked solution →How does a temperature change differ from a concentration change in its effect on an equilibrium?Read the answer and worked solution →What effect does adding a catalyst have on the equilibrium constant of a reaction?Read the answer and worked solution →What is the net effect of a catalyst on a reaction that is heading toward equilibrium?Read the answer and worked solution →Which award did Fritz Haber receive for making ammonia from its elements?Read the answer and worked solution →Nitrogen makes up most of the air, yet plants cannot use it directly. What has to happen first?Read the answer and worked solution →What do the three rows of an ICE table hold, in order?Read the answer and worked solution →Iodine and iodide both start at 1.000 x 10^-3 M and iodine settles at 6.61 x 10^-4 M as I3- forms. What is Kc?Read the answer and worked solution →For N2 + O2 forming 2NO, Kc = 4.1 x 10^-4 with [N2] = 0.036 M and [O2] = 0.0089 M. What is [NO]?Read the answer and worked solution →PCl5 at 1.00 M decomposes to PCl3 and Cl2 with Kc = 0.0211. What is [PCl5] at equilibrium?Read the answer and worked solution →A quadratic solved for an equilibrium change gives two roots. How is the unwanted one recognised?Read the answer and worked solution →When may the change x be neglected against an initial concentration in an equilibrium calculation?Read the answer and worked solution →For 0.15 M HCN with Kc = 4.9 x 10^-10, what is the hydrogen ion concentration at equilibrium?Read the answer and worked solution →

Worked practice questions

In a chemical equilibrium, what is true of the forward and the reverse reaction?

  1. They run at equal rates, so amounts hold steady
  2. They both stop once the amounts hold steady
  3. They run at rates in a fixed two to one ratio
  4. They take turns, only one running at a time
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Correct answer: A. They run at equal rates, so amounts hold steady

1. At equilibrium the forward reaction and the reverse reaction proceed at the same rate. 2. Because the two rates match, the concentrations of reactants and products no longer change. 3. Neither reaction stops, so equilibrium is a dynamic balance rather than a halt. 4. Rates locked in any ratio other than one to one would leave the concentrations drifting. _Source: OpenStax Chemistry (CC BY 4.0), Ch 13 "Fundamental Equilibrium Concepts", section 13.1 Chemical Equilibria_

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A reversible reaction run in a closed system usually gives what yield of products?

  1. Exactly 100 percent, with no reactant left
  2. Less than 100 percent, with reactant left over
  3. Exactly 50 percent, whatever the conditions
  4. A yield that keeps rising without any limit
Show answer and solution

Correct answer: B. Less than 100 percent, with reactant left over

1. In a closed system the products cannot leave, so the reverse reaction can proceed. 2. The mixture settles at a point where some reactant is still present alongside product. 3. The yield is therefore short of 100 percent, and a mixture is found at equilibrium. 4. Nothing forces the split to be 50 percent, so that value is an invented figure. _Source: OpenStax Chemistry (CC BY 4.0), Ch 13 "Fundamental Equilibrium Concepts", section 13.1 Chemical Equilibria_

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Liquid bromine is poured into a bottle. What condition lets a liquid to vapour equilibrium form?

  1. The bottle is capped so no vapour escapes
  2. The bottle is warmed above the boiling point
  3. The bottle is left open to the room air here
  4. The bottle is filled right up to the very brim
Show answer and solution

Correct answer: A. The bottle is capped so no vapour escapes

1. Evaporation and condensation are the forward and reverse steps of a physical change. 2. A capped bottle holds the vapour in, so condensation can build up to match evaporation. 3. Once the two rates match, the amounts of liquid and vapour stop changing. 4. If the bottle were left uncapped the vapour would escape and no equilibrium would be reached. _Source: OpenStax Chemistry (CC BY 4.0), Ch 13 "Fundamental Equilibrium Concepts", section 13.1 Chemical Equilibria_

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