JPJC 2026 Chemical Equilibrium Tutorial

2026 JPJC JC1 H2 Chemistry (9476) 1 Topic 7: Chemical Equilibrium JURONG PIONEER JUNIOR COLLEGE 2026 JC1 H2 Chemistry (9476) Tutorial 7: Chemical Equilibrium Level 1 – Self–Check Questions 1 Write expressions for the equilibrium constants, Kc and Kp (if applicable), for each of the following reactions. Assume th at all pressure terms are in Pa, gi ving the units of the equilibrium constants. (a) H2(g) + I2(g) ⇌ 2HI(g) (b) Ni(s) + 4CO(g) ⇌ Ni(CO)4(g) (c) CO2(aq) + H2O(l) + CaCO3(s) ⇌ Ca2+(aq) + 2HCO3−(aq) 2 For the reaction, 2X2(g) + Y2(g) ⇌ 2X2Y(g), the value of the equilibrium constant Kc is 5.00. Determine the value of Kc for each of the following equilibria, including its units. (a) 4X2(g) + 2Y2(g) ⇌ 4X2Y(g) (b) X2Y(g) ⇌ X2(g) + ½Y2(g) 3 The value of the equilibrium constant is 4.0 for the reaction below: CH3CO2H(l) + C2H5OH(l) ⇌ CH3CO2C2H5(l) + H2O(l) (a) Write an expression for the equilibrium constant, Kc, of the reverse reaction, i.e. the hydrolysis of ethyl ethanoate, stating its numerical value. (b) In an experiment, 2 mol of ethyl ethanoate and 2 mol of water are mixed. Calculate the number of moles of each substance present when equilibrium is reached. 4 9701 J2014 P23 Q3(b) modified Nitrogen dioxide exists in equilibrium with dinitrogen tetroxide, N2O4. 2NO2(g) ⇌ N2O4(g) ∆H < 0 2.00 mol of dinitrogen tetroxide was sealed in a container at 350 K. After equilibrium has been established, the total pressure was 140 kPa and the mixture of gases contained 1.84 mol of dinitrogen tetroxide. (a) Sketch a graph showing how the rates of the forward and reverse reactions change, from the time dinitrogen tetroxide starts to dissociate into nitrogen dioxide to the time the reaction reaches equilibrium. Label your two lines clearly. (b) (i) Give the expression for the equilibrium constant, Kp. (ii) Calculate the number of moles of NO2 present at equilibrium. (iii) Calculate the total number of moles of gases which are present at equilibrium and hence the mole fraction of each gas present at equilibrium. (iv) Calculate the partial pressure of each gas at equilibrium. (v) Calculate the value of the equilibrium constant, Kp, at 350 K, including its units.

2026 JPJC JC1 H2 Chemistry (9476) 2 Topic 7: Chemical Equilibrium Level 2 – Application Questions Kc and Kp calculations 5 The equilibrium mixture in a 3 dm3 vessel at 673 K and 1.5 atm contains 0.50 mol of sulfur dioxide, 0.30 mol of oxygen and 4.80 mol of sulfur trioxide. 2SO2(g) + O2(g) ⇌ 2SO3(g) Calculate the equilibrium constants, Kc and Kp. 6 The Contact process for the manufacture of sulfuric acid is as follows. 2SO2 (g) + O2(g) ⇌ 2SO3 (g) ∆H = -197 kJ mol-1 When a 2:1 mole ratio of SO 2 and O2 at a total initial pressure of 3 atm is passed over a catalyst at 430 oC, the partial pressure of SO3 at equilibrium is found to be 1.9 atm. (a) Calculate the partial pressures of SO 2 and O 2 at equilibrium and hence the new total pressure and the percentage conversion of SO2 into SO3. (b) Write an expression for Kp for this reaction and calculate its value. Kp calculations and Le Chatelier’s principle [N2022/P3/Q2(c) modified] 7 The equation for the Haber process for manufacturing ammonia is shown. 3H2(g) + N2(g) ⇌ 2NH3(g) ----- Eqm (1) H = -92 kJ mol-1210 kJ mol-1 A mixture of H2 and N2 in the molar ratio 3:1 is added to a sealed vessel and heated to 450 o C with an iron catalyst. At equilibrium, 40% of the nitrogen has reacted. The total pressure in the vessel is 2.80 x 104 kPa at equilibrium. (a) Write an expression for the equilibrium constant, Kp for this reaction Use your expression to calculate the value of Kp for the reaction. Include its units. (b) Predict, with reasoning, how the position of equilibrium and the equilibrium constant might change, if any, for the above reaction, when (i) temperature is decreased (ii) ammonia gas is added Kp calculations and effect of catalyst on equilibrium 8 Methanol is a useful fuel that can be manufactured from a mixture of carbon monoxide and hydrogen, at high pressure and a temperature of 300 C. CO(g) + 2H2(g) ⇌ CH3OH(g) ----- Eqm (1) (a) Predict, with reasoning, how the position of equilibrium and the equilibrium constant might change, if any, for the above reaction, when a catalyst is added (b) At an initial total pressure of 100 atm, an equimolar mixture of carbon monoxide and hydrogen is allowed to reach equilibrium. At equilibrium, 95% of the original sample of H2 had reacted. Calculate the value of Kp at 300 °C. State the units.

2026 JPJC JC1 H2 Chemistry (9476) 3 Topic 7: Chemical Equilibrium (c) Based on the data given below for an equilibrium mixture of gaseous CO, H2 and CH3OH, predict whether the reaction is exothermic or endothermic. Explain your answer. CO(g) + 2H2(g) ⇌ CH3OH(g) Temperature / K 500 800 Value of Kc 37 0.016 N2016/III/1(f) modified 9 One version of the Fischer -Tropsch process for manufacturing methane is the reaction of carbon monoxide with hydrogen. CO(g) + 3H2(g) CH4(g) + H2O(g) (a) Write an expression for the equilibrium constant, Kp, for this reaction, and state its units. [2] (b) A mixture of CO and H2 in a 1:3 molar ratio was introduced into a sealed vessel and heated to 1200 K. At equilibrium it was found that the total pressure was 32 atm, and the mole fractions of CO and CH4 were 0.19 and 0.12 respectively. (i) Calculate the equilibrium partial pressures of the two reactants and the two products. [2] (ii) Use these data to calculate the value of Kp. [1] (c) At time = t min, the volume of the reaction mixture was suddenly halved. Complete the graph until a new equilibrium is reached for each of reactants and product formed. Briefly explain the graph you have drawn. [4]

2026 JPJC JC1 H2 Chemistry (9476) 4 Topic 7: Chemical Equilibrium 10 A reaction is represented by the following equation. xC(g)  yA(g) + B(g); H > 0 The reaction was studied by monitoring the amounts of C, A and B over time in a reaction vessel with a fixed volume of 2 dm3. The initial amounts of C, A and B used were 1.80 mol, 0.40 mol and 0.40 mol respectively. Fig 1 below shows the results that were obtained. Fig. 1 (a) Determine the values of x and y in the above equation, showing clearly any calculations or reasoning. (b) Calculate the equilibrium constant, Kc, immediately before time t1. Include units in your answer. (d) Another change was made to the system at time t2. State and explain the change that was made. (e) At time t3, an inert gas was added to the system at constant volume and temperature. Sketch the effect of this change on the amounts of C, A and B in the space after the dotted vertical line on Fig.1. Explain your answer.

2026 JPJC JC1 H2 Chemistry (9476) 5 Topic 7: Chemical Equilibrium Multiple choice questions 11 [N2008/I/7] A pure sample of N 2O4 (l) is introduced into an evacuated vessel. The vessel, of constant volume, is heated to a constant temperature such that the equilibrium below is established. 2NO2 (g) ⇌ 2NO(g) + O2 (g) The value of the pressure p is then found to be 20% greater than if only NO2 (g) were present. What is the mole fraction, x, of oxygen in this equilibrium mixture? A 0.17 B 0.20 C 0.33 D 0.40 12 [N2020/I/7] 0.040 mol of H I(g) is placed in a sealed vessel and allowed to reach equilibrium, at a pressure of 1.0 atm. H2(g) + I2(g) ⇌ 2HI(g) Kp = 54 at 700 K What is the partial pressure of HI(g) in the equilibrium mixture? A 0.06 atm B 0.79 atm C 0.88 atm D 0.96 atm 13 [N2008/I/12] Which statement is correct about a reaction for which the equilibrium constant is independent of