52 problems
1PRACTICE PROBLEMConsider the following hypothetical decomposition reaction XY → X + Y. The vessel on the right represents an equilibrium mixture of X atoms (green sphere), Y atoms (purple sphere), and XY molecules. In which direction will the reaction proceed when the stopco*ck is opened and the contents of the two vessels are allowed to mix? Justify your answer.
2PRACTICE PROBLEMConsider the following hypothetical reaction: AX4(g) + X2(g) ⇌ AX6(g). Determine whether the reaction is endothermic or exothermic given that Kp = 0.580 at T = 900 K and Kc = 0.158 at T = 1000 K and justify your answer. Is this the same as predicted using bond energies?
3PRACTICE PROBLEMConsider the following equilibrium reaction: 2 NOBr(g) + Cl2(g) ⇌ 2 NO(g) + 2 BrCl(g), ΔH° = +47.4 kJ.(a) How will the concentration of NO change when the temperature of the system is lowered?(b) How will the equilibrium constant (Kc) change when the temperature of the system is increased?Explain your answer using Le Chatelier's principle.
4PRACTICE PROBLEMThe equilibrium composition of the exothermic reaction 2 L → L2 at 750 K is shown in the following figure:Which of the following diagrams shows the equilibrium mixture after increasing the temperature of the system?
5PRACTICE PROBLEMTwo equilibrium states of the dissociation reaction PQ ⇌ P + Q at two different temperatures are shown in the diagrams below.Identify whether the reaction is exothermic or endothermic and justify your answer using Le Chatelier's principle.
6PRACTICE PROBLEMThe interconversion of the purple CrCl3 and green [Cr(H2O)6]3+ ion shown in the following reaction is endothermic.CrCl3(aq) + 6 H2O(aq) ⇌ [Cr(H2O)6]3+(aq) + 3 Cl−(aq)What happens to the equilibrium concentration of CrCl3 in a solution of the reaction when the solution is diluted with water?
7PRACTICE PROBLEMConsider the equilibrium reaction between ethanol and acetic acid: CH3CH2OH(aq) + CH3COOH(aq) ⇌ CH3CO2CH2CH3(aq) + H2O(l). Will the equilibrium amounts of the reactants and products increase, decrease, or remain the same after a catalyst is added to the mixture?
8PRACTICE PROBLEMConsider the following reaction at equilibrium: U(s) + F2(g) ⇌ UF6(g). Identify in which direction the reaction will shift after U(s) is added to the mixture.
9PRACTICE PROBLEMThe initial and equilibrium state of the endothermic decomposition of P(g) molecules (purple spheres) to Q(g) molecules (orange spheres) are illustrated in the diagram below. What will happen to the number of P(g) molecules if the pressure of the system is increased by adding an inert gas?
10PRACTICE PROBLEMThe reaction N2(g) + 3 H2(g) ⇌ 2 NH3(g) has the following values at 298 K: Kp = 6.2×105 and ΔH° = –92.2 kJ. Consider the following changes below which will result in an increase in the partial pressure of NH3 at equilibrium. Which of the changes will result in the highest increase in the partial pressure of NH3? Justify your answer.I. Adding 0.20 mol of N2III. Adding 0.20 mol of H2III. Lowering the temperature to 250 KA. Adding 0.20 mol of N2 will result in the highest increase in partial pressure of NH3 because it will produce a greater amount of NH3.B. Adding 0.20 mol of H2 will result in the highest increase in partial pressure of NH3 because it is the limiting reactant.C. Lowering the temperature to 250 K will result in the highest increase in partial pressure of NH3 because it will shift the equilibrium reaction to the right.D. All of the above will result in the same increase in the partial pressure ofNH3.
11PRACTICE PROBLEMAmmonium chloride decomposes into ammonia and hydrogen chloride according to the following reaction:NH4Cl(s) ⇌ NH3(g) + HCl(g)An equilibrium mixture ofNH4Cl(s), NH3(g), and HCl(g) is in a closed reaction vessel. What will happen to the number of moles of NH3 when HCl is added to the mixture?
12PRACTICE PROBLEMRefer to the following equilibrium reaction:Zn2+(aq) + 2 Cl–(aq) ⇌ ZnCl2(s)Using Le Chatelier's principle, determine the change in the amount of ZnCl2 when OH– is added to the solution to produce the complex ion [Zn(OH)4]2–.
13PRACTICE PROBLEMMethane can be produced from carbon monoxide via catalytic hydrogenation according to the following reaction:CO(g) + 3 H2(g) ⇌ CH4(g) + H2O(g) ΔH° = –206 kJA reaction vessel contains an equilibrium mixture of CO(g), H2(g), CH4(g), and H2O(g). Determine how will the amount of CO change if the pressure of the system is decreased by removing some H2(g).
14PRACTICE PROBLEMThe dissociation of I2 to its atoms has an equilibrium constant (Kc) of 4.6×10–7 at 800 K.I2(g) ⇌ 2 I(g)Does the equilibrium ratio of the two concentrations change by adding I2 or by reducing the volume of the container? Justify your answer.
15PRACTICE PROBLEMConsider the hypothetical reaction P2 + Q2 ⇌ 2 PQ. Provided in the table below are the rate constants of the forward and reverse reactions at different temperatures.Determine if the reaction is endothermic or exothermic and justify your answer.
16PRACTICE PROBLEMAmines can be prepared from carbonyl compounds via reductive amination. The intermediate formed in the reaction is called imine. The following reaction illustrates a synthesis of an amine via reductive amination using sodium cyanoborohydride (NaBH3CN):In order to increase the formation of the intermediate in the reaction, which of the following changes can you do based on Le Chatelier's principle?
17PRACTICE PROBLEMAt 298 K, a 3.00 mol sample of SO3 is added to a 3.00 L vessel; 45% of SO3 decomposes into SO2 and O2: 2 SO3(g) ⇌ 2 SO2(g) + O2(g). If the reaction was carried out in a 1.00 L vessel, will the percent of SO3 that decomposes increase, decrease, or remain the same?
18PRACTICE PROBLEMConsider the equilibrium N2(g) + 3 H2(g) ⇌ 2 NH3(g) ΔH = 92 kJ. Does increasing the volume of the container (at constant temperature) increase, decrease, or not affect the amount of NH3(g) at equilibrium?
19PRACTICE PROBLEMThe equilibrium As4O6(s) + 6 C(s) ⇌ As4(g) + 6 CO(g) was studied in an experiment. Equal amounts of As4O6(s) and C(s) were added to reaction vessels A and B as shown below and allowed to reach equilibrium.Which of the following statements is true?
20PRACTICE PROBLEMConsider the following reaction: ClNO2(g) + NO(g) ⇌ NO2(g) + ClNO(g). Adding a catalyst would increase the yield of ClNO at equilibrium. Is this statement correct?
21PRACTICE PROBLEMConsider the following reaction: ClNO2(g) + NO(g) ⇌ NO2(g) + ClNO(g). If you decrease the concentration of NO, would the yield of ClNO at equilibrium increase, decrease, or remain the same?
22PRACTICE PROBLEMConsider the equilibrium reaction below:2 NO(g) + Cl2(g) ⇌ 2 NOCl(g)What is the effect of removing Cl2(g) from the equilibrium mixture?
23PRACTICE PROBLEMHydrogen gas and iodine gas react to form gaseous hydrogen iodide: H2(g) + I2(g) ⇌ 2 HI(g). Would a change in pressure affect the yield of the reaction? If yes, would an increase or decrease in pressure favor the formation of HI(g)?
24PRACTICE PROBLEMIf the temperature of the dissociation of P4 to P2 is increased by 120 K, will the equilibrium constant become larger or smaller?P4(g) ⇌ 2 P2(g)
25PRACTICE PROBLEMPhosphorus pentachloride dissociates to produce gaseous PCl3 and Cl2: PCl5(g) ⇌ PCl3(g) + Cl2(g). To further promote the dissociation of phosphorus pentachloride, would you increase or decrease the pressure of the system?
26PRACTICE PROBLEMThe reaction ofNOwith O2 produces NO2.2 NO (g) + O2 (g) ⇌ 2 NO2 (g)To maximize the equilibrium yield of NO2, should the temperature be increased or decreased? (Hint: use thermochemical data to calculate ΔH°)
27PRACTICE PROBLEMConsider a reaction occurring at 15 °C that is represented by the following equation 3 M(g) ⇌ 2 N(g). A reaction vessel initially contains 1.5 atm of M. Once equilibrium has been established, the final pressure of M is 0.55 atm. Which of the following scenario will increase the yield of N?
28PRACTICE PROBLEMAt 358 K the esterification of an organic acid and an alcohol has a forward reaction rate constant of 2.25×10−4 M−1•s−1 and a reverse rate constant of 1.85×10−4 M−1•s−1. When the temperature is increased to 368 K, the rate constants for the same reaction have values of kf = 3.14×10−4 M−1•s−1 and kr = 1.97×10−4 M−1•s−1. Is the reverse reaction endothermic or exothermic?
29PRACTICE PROBLEMHow does increasing the temperature affect the following reaction at equilibrium?N2O(g) + 3 H2(g) ⇌ N2H4(l) + H2O(l) ΔH = -317 kJ
30PRACTICE PROBLEMOxygen binds with hemoglobin found in our blood via the following equilibrium reaction:HbH+(aq) + O2(aq)⇌ HbO2(aq) + H+(aq)where Hb is hemoglobin. Since this reaction is pH sensitive, normal human blood has a controlled pH range of 7.35 to 7.45. Which of the following statements is correct?a. If the pH of blood is too low, there will be lessHbO2, and the capacity of hemoglobin to carry oxygen will decrease.b. If the pH of blood is too high, there will be less HbO2, and the capacity of hemoglobin to carry oxygen will decrease.c.If the pH of blood is too low, there will be lessHbO2, and the capacity of hemoglobin to carry oxygen will increase.d. None of the above
31PRACTICE PROBLEMClassify the autoionization of water as exothermic or endothermic given that as the temperature decreases the value of the Kw also decreases.
32PRACTICE PROBLEMWhen sulfur dioxide in the air mixes with water, it becomes sulfuric acid which is a component of acid rain.2 SO2 (g) + O2 (g) → 2 SO3 (g)SO3 (g) + H2O (l) → H2SO4 (aq)What is the effect of the increase in the amount of sulfur dioxide due to burning more fossil fuels on the pH of the rain? What is its effect on structures made of limestones (CaCO3) such as coral reefs and marine shells?
33PRACTICE PROBLEMWhich of the following will occur when the volume is increased for the following reaction at equilibrium?NH2COONH4 (g) ⇌ 2 NH3 (g) + CO2 (g)
34PRACTICE PROBLEMWhich of the following will occur when the volume is decreased for the following reaction at equilibrium?2 H2Te (g) ⇌ 2 H2 (g) + Te2 (g)
35PRACTICE PROBLEMWhich of the following will increase the formation of NH3 in the following exothermic reaction at equilibrium?N2 (g) + 3 H2 (g) ⇌ 2 NH3 (g)
36PRACTICE PROBLEMWhich of the following statements is correct for the following endothermic reaction at equilibrium?2 CO2 + O2⇌ 2 CO3
37PRACTICE PROBLEMFor the given endothermic reaction,N2 (g) + O2 (g) ⇌ 2 NO (g)which of the following statement is true?
38PRACTICE PROBLEMWhich of the following will not affect the concentration of NH3 in the following exothermic reaction at equilibrium?N2 (g) + 3 H2 (g) ⇌ 2 NH3 (g)
39PRACTICE PROBLEMWhich of the following will increase the formation ofNH3 in the following exothermic reaction at equilibrium?N2 (g) + 3 H2 (g) ⇌ 2 NH3 (g)a. increasing N2 in the reactionb. decreasingH2in the reactionc. decreasingN2 in the reactiond. removingNH3 as it forms in the reaction
40PRACTICE PROBLEMWhich of the following will occur when O2 is added to the following reaction at equilibrium?CH4 (g) + O2 (g) ⇌ CO2 (g) + H2O (g)
41PRACTICE PROBLEMWhich of the following will occur when Cl2 is removed as it forms in the following reaction at equilibrium?CCl2O (g) ⇌ CO (g) + Cl2(g)
42PRACTICE PROBLEMWhich of the following will occur when the amount of CO is increased in the following reaction at equilibrium?CCl2O (g) ⇌ CO (g) + Cl2 (g)
43PRACTICE PROBLEMDetermine the condition that will increase the amount of C4H8Br2 at equilibrium for the endothermic reaction:C4H8(g) + Cl2 (g) ⇌ C4H8Br2 (g)a. removing Cl2from the mixtureb. increasing the volume of the reactionc. increasing the amount ofC4H8d. increasing the temperature of the reaction
44PRACTICE PROBLEMDetermine the condition that will increase the amount of C4H8 at equilibrium for the exothermic reaction:C4H8(g) + Br2 (g) ⇌ C4H8Br2 (g)
45PRACTICE PROBLEMThe oxidation of hydrogen selenide (H2Se) with oxygen produces selenium dioxide (SeO2) and water:2 H2Se(g) + 3 O2(g) ⇌ 2 SeO2(s) + 2 H2O(g)What will happen to the equilibrium state when the volume of the reaction vessel is decreased?
46PRACTICE PROBLEMNitric acid (HNO3) is prepared industrially through the Ostwald process. One of the raw materials used in the process is ammonia (NH3). Ammonia is oxidized to produce nitric oxide (NO) which undergoes a series of different reactions and finally produces nitric acid.4 NH3(g)+ 5 O2(g) ⇌ 4 NO(g)+ 6 H2O(g) ΔH° = −905.2 kJ/molIdentify what will happen to the equilibrium direction and the value of the equilibrium constant (Kc) when the temperature of the reaction mixture is increased.
47PRACTICE PROBLEMLead nitrate (Pb(NO3)2) can be decomposed thermally into lead oxide (PbO), nitrogen dioxide (NO2), and oxygen (O2):2 Pb(NO3)2(s) ⇌ PbO + 4 NO2(g) + O2(g)A higher yield of NO2 and O2 will be obtained, if the reaction were carried out in:
48PRACTICE PROBLEMThe conversion of sulfur dioxide (SO2) to sulfur trioxide (SO3) is a reversible reaction:2 SO2(g) + O2(g) ⇌ 2 SO3(g)Identify what will happen to the direction of equilibrium when each of the following changes is applied:a) More SO3 is added to the reaction mixture.b) O2 is removed from the reaction mixture.c) More SO2 is added to the reaction mixture.d) Neon gas is added to the reaction mixture.
49PRACTICE PROBLEMWhich of the following reversible reactions can be pushed towards the products' side by reducing pressure?PCl3(g) + Cl2(g) ⇌ PCl5(g)CaCO3(s) ⇌ CaO(s) + CO2(g)N2(g) + 3 H2(g) ⇌ 2 NH3(g)CH4(g) + H2O(g) ⇌ CO(g) + 3 H2(g)2 SO2(g) + O2(g) ⇌ 2 SO3(g)
50PRACTICE PROBLEMCoal can be converted to natural gas (methane, CH4) by heating it with hydrogen in presence of a suitable catalyst:C(s) + 2 H2(g) ⇌ CH4(g)Which of the following changes will push the reaction towards the product side?A) A catalyst is added/removed from the reaction vessel.B) More hydrogen gas (H2) is added to the reaction mixture.C) The volume of the reaction vessel is decreased.D) Neon gas is added to the reaction mixture.E) Temperature of the reaction mixture is increased.F) More coal is added to the reaction mixture.
51PRACTICE PROBLEMThe binding of oxygen by hemoglobin in the blood involves the equilibrium reaction:HbH+(aq) + O2(aq) ⇌ HbO2(aq) + H+(aq)In this equation, Hb is hemoglobin. The pH of normal human blood is highly controlled within a range of 7.35 to 7.45. Given the above equilibrium, why is this important? What would happen to the oxygen-carrying capacity of hemoglobin if blood became too acidic (a dangerous condition known as acidosis)?
52PRACTICE PROBLEMConsider the exothermic reaction:C2H4(g) + Br2(g) ⇌ C2H4Br2(g)If you were trying to maximize the amount of C2H4Br2 produced, which tactic might you try? Assume that the reaction mixture reaches equilibrium.a. Increasing the reaction volume.b. removing C2H4Br2 from the reaction mixture as it forms.c. lowering the reaction temperatured. adding Br2.
