20 Module 5: Equilibrium and Acid Reactions Practice Questions for HSC Chemistry 

Factors that Affect Equilibrium 

Question 6

Account for the effect of increased temperature and increased volume on the reaction between nitrogen dioxide and dinitrogen tetraoxide using the Le Chatelier’s principle. (4 marks)

(L2.1: Investigate the effects of temperature, concentration, volume and/or pressure on a system at equilibrium and explain how Le Chatelier’s principle can be used to predict such effects)

Question 7

Using the Le Chatelier’s principle, explain how the addition of NaCl can be used to produce more Fe3+ and SCN– ions in the following reaction. (4 marks)

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(L2.1: Investigate the effects of temperature, concentration, volume and/or pressure on a system at equilibrium and explain how Le Chatelier’s principle can be used to predict such effects)

Question 8

Using the Le Chatelier’s principle, deduce how we can increase the yield of Co(H2O)62+ by temperature, concentration and pressure. The chemical reaction is as follows: 

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(L2.1: Investigate the effects of temperature, concentration, volume and/or pressure on a system at equilibrium and explain how Le Chatelier’s principle can be used to predict such effects)

Question 9

Consider the reaction in question 8. Explain whether the addition of NaCl increases the production of its products using the collision theory. (4 marks)

(L2.2: Explain the overall observations about equilibrium in terms of the collision theory) 

Question 10

Predict the most likely position of the equilibrium in the following conditions. (4 marks)

a) Low activation energy in forward reaction but high activation energy in reverse reaction 

b) High activation energy in forward reaction but low activation energy in reverse reaction 

c) Negative heat of reaction within high temperatures 

d) Negative heat of reaction within low temperatures 

(L2.3: Examine how the activation energy and heat of reaction affect the position of equilibrium) 

Question 11

Write the equilibrium expression for each of the reactions below (3 marks): 

(L3.1: Deduce the equilibrium expression (in terms of Keq) for homogeneous reactions occurring in solution) 

Question 12

0.5 moles of N₂ gas was added to a 10L chamber with O₂ gas which produced 0.3 moles of NO₂ gas after reaching equilibrium. What was the equilibrium concentration of all three substances in this reaction? Include relevant chemical equations. (4 marks) 

(L3.2: Perform calculations to find the value of Keq and concentrations of substances within an equilibrium system and use these values to make predictions on the direction in which a reaction may proceed) 

Question 13

Explain how an increase in temperature can affect the Keq of an endothermic and exothermic reaction. (4 marks)

(L3.3: Qualitatively analyse the effect of temperature on the value of Keq)

Question 14

During the practical that investigates the Keq of iron (III) thiocyanate equilibrium, students obtained a different Keq value to that of the theoretical value. Suggest a source of error for this. (3 marks)

(L3.4: Conduct an investigation to determine Keq of a chemical equilibrium system, for example: Keq of the iron (III) thiocyanate equilibrium) 

Question 15

Deduce what would be observed in the following conditions. (6 marks)

(L3.5: Explore the use of Keq for different types of chemical reactions, including but not limited to: Dissociation of ionic solutions, Dissociation of acids and bases)

Solution Equilibria 

Question 16

Explain how the dissolution of cations differ to the dissolution of anions in water. Use diagrams if appropriate. (4 marks) 

(L4.1: Describe and analyse the processes involved in the dissolution of ionic compounds in water)

Question 17

How do Aboriginal and Torres Strait Islander People utilise the solubility equilibria to remove toxins in cycad fruits? (4 marks) 

(L4.2: Investigate the use of solubility equilibria by Aboriginal and Torres Strait Islander Peoples when removing toxicity from foods, for example: Toxins in cycad fruit)

Question 18

Complete the following table. (9 marks)

(L4.3: Conduct an investigation to determine solubility rules, and predict and analyse the composition of substances when two ionic solutions are mixed, for example: Potassium chloride and silver nitrate, Potassium iodide and lead nitrate, Sodium sulfate and barium nitrate)

Question 19

Calculate the the following (6 marks): 

a) What is the solubility of Sr^2-when the Ksp of strontium sulfate is 3.44×10^-7? 

b) What is the solubility of CO₃^2-when the Ksp of calcium carbonate is 3.36×10^-9? 

c) What is the solubility of CrO₄^2- when the Ksp  of barium chromate is 1.2×10^-10

(L4.4: Derive equilibrium expressions for saturated solutions in terms of Ksp and calculate the solubility of an ionic substance from its Ksp value) 

Question 20

25.0 mL of 0.0020 M potassium chromate are mixed with 75.0 mL of 0.000125 M lead(II) nitrate. Will a precipitate of lead(II) chromate form. Ksp of lead(II) chromate is 1.8 x 10^-14 (3 marks)

(L4.5: Predict the formation of a precipitate when given the standard reference values for Ksp)