Chem Exam 2

For the reaction given below, 2.00 moles of A and 3.00 moles of B are placed in a 6.00-L container. At equilibrium, the concentration of A is 0.292 mol/L. What is the concentration of B at equilibrium? Answers: 0.292 mol/L 0.417 mol/L 0.500 mol/L 0.584 mol/L none of these

0.417

If, at a given temperature, the equilibrium constant for the reaction H 2( g) + Cl 2( g) 2HCl( g) is K p, then the equilibrium constant for the reaction HCl( g) H 2( g) + Cl 2 ( g) can be represented as:

1 over square root of Kp

Consider the chemical system CO + Cl 2 COCl 2; K = 4.6 × 10 9 L/mol.Reference: Ref 13-1 How do the equilibrium concentrations of the reactants compare to the equilibrium concentration of the product? Answers: They are much smaller. They are much bigger. They are about the same. They have to be exactly equal. You can't tell from the information given.

A

Consider the following equilibrium: 2H 2( g) + X 2( g) 2H 2X( g) + energyReference: Ref 13-9 Addition of X 2 to a system described by the above equilibrium Answers: will cause [H2] to decrease will cause [X2] to decrease will cause [H2X] to decrease will have no effect cannot possibly be carried out

A

Consider the following equilibrium: 2H 2( g) + X 2( g) 2H 2X( g) + energyReference: Ref 13-9 Increasing the pressure by decreasing the volume will cause Answers: the reaction to occur to produce H2X the reaction to occur to produce H2 and X2 the reaction to occur to produce H2 but no more X2 no reaction to occur X2 to dissociate

A

Equilibrium is reached in chemical reactions when: Answers: The rates of the forward and reverse reactions become equal. The concentrations of reactants and products become equal. The temperature shows a sharp rise. All chemical reactions stop. The forward reaction stops.

A

For the equilibrium system: CO 2( g) + H 2( g) CO( g) + H 2O( g) H = +42 kJ/mol K equals 1.6 at 1260 K. If 0.15 mol each of CO 2, H 2, CO, and H 2O (all at 1260 K) were placed in a 1.0-L thermally insulated vessel that was also at 1260 K, then as the system came to equilibrium: The temperature would decrease and the mass of CO2 would increase. The temperature would decrease and the mass of CO2 would decrease. The temperature would remain constant and the mass of CO2 would increase. The temperature would increase and the mass of CO2 would increase. The temperature would increase and the mass of CO2 would decrease.

A

Given the equation 2A( g) 2B( g) + C( g). At a particular temperature, K = 1.6 × 10 4. Reference: Ref 13-5 Addition of chemical B to an equilibrium mixture of the above will Answers: cause [A] to increase cause [C] to increase have no effect cannot be determined none of the above

A

Given the equation 2A( g) 2B( g) + C( g). At a particular temperature, K = 1.6 × 10 4. Reference: Ref 13-5 If you mixed 5.0 mol B, 0.10 mol C, and 0.0010 mol A in a one-liter container, which direction would the reaction initially proceed? To the left. To the right. The above mixture is the equilibrium mixture. Cannot tell from the information given. None of these (A-D).

A

Given the equation 2A( g) 2B( g) + C( g). At a particular temperature, K = 1.6 × 10 4. Reference: Ref 13-5 Raising the pressure by lowering the volume of the container will cause [A] to increase cause [B] to increase have no effect cannot be determined none of the above

A

The value of the equilibrium constant, K, is dependent on: I. the temperature of the system II. the nature of the reactants and products III. the concentration of the reactants IV. the concentration of the products Answers: I, II II, III III, IV It is dependent on three of the above choices. It is not dependent on any of the above choices.

A

Which of the following statements is true? Answers: When two opposing processes are proceeding at identical rates, the system is at equilibrium. Catalysts are an effective means of changing the position of an equilibrium. The concentration of the products equals that of reactants and is constant at equilibrium. An endothermic reaction shifts toward reactants when heat is added to the reaction. None of the above statements is true.

A

At -80°C, K for the reaction N 2O 4( g) 2NO 2( g) is 4.66 10 -8. We introduce 0.056 mole of N 2O 4 into a 1.0-L vessel at -80°C and let equilibrium be established. The total pressure in the system at equilibrium will be: 0.37 atm 0.89 atm 1.6 atm 0.056 atm none of these

B

CS 2( g) + 3Cl 2( g) CCl 4( g) + S 2Cl 2( g) At a given temperature, the reaction above is at equilibrium when [CS 2] = 0.050 M, [Cl 2] = 0.25 M, [CCl 4] = 0.15 M, and [S 2Cl 2] = 0.35 M. What would be the direction of the reaction when the reactants and products have the following concentrations: CS 2 = 0.15 M, Cl 2 = 0.20 M, CCl 4 = 0.32 M, and S 2Cl 2 = 0.26 M? Answers: to the right to the left no change cannot predict unless we know the temperature cannot predict unless we know whether the reaction is endothermic or exothermic

B

Consider the following equilibrium: 2H 2( g) + X 2( g) 2H 2X( g) + energyReference: Ref 13-9 Increasing the temperature will cause the reaction to occur to produce H2X the reaction to occur to produce H2 and X2 the reaction to occur to produce H2 but no more X2 no reaction to occur an explosion

B

Consider the gaseous reaction CO( g) + Cl 2( g) COCl 2( g). What is the expression for K p in terms of K? K(RT) K/(RT) K(RT)2 K/(RT)2 1/K(RT)

B

For a particular system at a particular temperature there ______ equilibrium constant(s) and there _______ equilibrium position(s). Answers: are infinite; is one is one; are infinite is one; is one are infinite; are infinite none of these

B

For the reaction below, K p = 1.16 at 800.°C. CaCO 3( s) CaO( s) + CO 2( g) If a 22.2-gram sample of CaCO 3 is put into a 10.0-L container and heated to 800.°C, what percent of the CaCO 3 will react to reach equilibrium? 30.7% 59.4% 79.7% 100.0% none of these

B

Given the equation 2A( g) 2B( g) + C( g). At a particular temperature, K = 1.6 × 10 4. Reference: Ref 13-5 At a higher temperature, K = 1.8 × 10 -5. Placing the equilibrium mixture in an ice bath (thus lowering the temperature) will cause [A] to increase cause [B] to increase have no effect cannot be determined none of the above

B

Nitrogen gas (N 2) reacts with hydrogen gas (H 2) to form ammonia (NH 3). At 200°C in a closed container, 1.0 atm of nitrogen gas is mixed with 2.0 atm of hydrogen gas. At equilibrium, the total pressure is 2.0 atm. Calculate the partial pressure of hydrogen gas at equilibrium. Answers: 2.0 atm 0.50 atm 1.5 atm 0.0 atm none of these

B

The following questions refer to the equilibrium shown here: 4NH 3( g) + 5O 2( g) 4NO( g) + 6H 2O( g)Reference: Ref 13-8 For a certain reaction at 25.0°C, the value of K is 1.2 × 10 -3. At 50.0°C the value of K is 3.4 × 10 -1. This means that the reaction is Answers: exothermic endothermic never favorable more information needed none of these (A-D)

B

The reaction quotient for a system is 7.2 × 10 2. If the equilibrium constant for the system is 36, what will happen as equilibrium is approached? Answers: There will be a net gain in product. There will be a net gain in reactant. There will be a net gain in both product and reactant. There will be no net gain in either product or reactant. The equilibrium constant will decrease until it equals the reaction quotient.

B

the questions below refer to the following system: Co(H 2O) 6 2+ + 4 Cl - CoCl 4 2- + 6H 2O (pink) (blue) When cobalt(II) chloride is added to pure water, the Co 2+ ions hydrate. The hydrated form then reacts with the Cl - ions to set up the equilibrium shown here.Reference: Ref 13-7 Which statement below describes the change that the system will undergo if silver nitrate is added? It should become more blue. It should become more pink. Water will be produced. The silver ion will react with the CoCl42-. Nothing will change.

B

A 3.00-liter flask initially contains 3.00 mol of gas A and 1.50 mol of gas B. Gas A decomposes according to the following reaction: 3A 2B + C The equilibrium concentration of gas C is 0.130 mol/L. Determine the equilibrium concentration of gas B. Answers: 0.130 M 0.630 M 0.760 M 0.240 M 0.260 M

C

Carbon disulfide and chlorine react according to the following equation: CS 2( g) + 3Cl 2( g) S 2Cl 2( g) + CCl 4( g) When 2.94 mol of CS 2 and 5.60 mol of Cl 2 are placed in a 2.00-L container and allowed to come to equilibrium, the mixture is found to contain 0.580 mol of CCl 4. How many moles of Cl 2 are present at equilibrium? 2.360 mol 0.580 mol 3.86 mol 4.44 mol 1.93 mol

C

Exactly 1.0 mol N 2O 4 is placed in an empty 1.0-L container and is allowed to reach equilibrium described by the equation N 2O 4( g) 2NO 2( g) If at equilibrium the N 2O 4 is 25% dissociated, what is the value of the equilibrium constant, K c, for the reaction under these conditions? 0.67 0.33 3.0 0.25 0.083

C

Which of the following is true for a system whose equilibrium constant is relatively small? It will take a short time to reach equilibrium. It will take a long time to reach equilibrium. The equilibrium lies to the left. The equilibrium lies to the right. Two of these.

C

A mixture of nitrogen and hydrogen was allowed to come to equilibrium at a given temperature. 3H 2 + N 2 2NH 3 An analysis of the mixture at equilibrium revealed 2.0 mol N 2, 3.1 mol H 2, and 1.9 mol NH 3. How many moles of H 2 were present at the beginning of the reaction? 3.1 4.6 5.0 5.9 4.4

D

A sample of solid NH 4NO 3 was placed in an evacuated container and then heated so that it decomposed explosively according to the following equation: NH 4NO 3( s) N 2O( g) + 2H 2O( g) At equilibrium the total pressure in the container was found to be 2.61 atm at a temperature of 500.°C. Calculate K p. 0.757 1.51 0.659 2.63 71.1

D

Calculate K p for using the following data: K p = 2.4 × 10 6 K p = 1.8 × 10 37 Answers: 4.3 × 1043 2.2 × 1043 3.2 × 10-25 5.7 × 10-13 1.0 × 10-12

D

Calculate K p for using the following data: K p = 2.4 × 10 6 K p = 1.8 × 10 37 4.3 × 1043 2.2 × 1043 3.2 × 10-25 5.7 × 10-13 1.0 × 10-12

D

Consider the chemical system CO + Cl 2 COCl 2; K = 4.6 × 10 9 L/mol.Reference: Ref 13-1 If the concentration of the product were to double, what would happen to the equilibrium constant? Answers: It would double its value. It would become half its current value. It would quadruple its value. It would not change its value. It would depend on the initial conditions of the product.

D

Consider the following equilibrium: H 2( g) + I 2( s) 2HI( g)Reference: Ref 13-2 Which of the following statements about the equilibrium is false? If the system is heated, the right side is favored. This is a heterogeneous equilibrium. If the pressure on the system is increased by changing the volume, the left side is favored. Adding more H2(g) increases the equilibrium constant. Removing HI as it forms forces the equilibrium to the right.

D

Consider the reaction A( g) + B( g) C( g) + D( g). You have the gases A, B, C, and D at equilibrium. Upon adding gas A, the value of K: increases, because by adding A more products are made, increasing the product to reactant ratio decreases, because A is a reactant so the product to reactant ratio decreases does not change, because A does not figure into the product to reactant ratio does not change, as long as the temperature is constant depends on whether the reaction is endothermic or exothermic

D

For the reaction N 2O 4( g) 2NO 2( g), K p = 0.148 at a temperature of 298 K. What is K p for the following reaction? 6NO 2( g) 3N 2O 4( g) 6.76 0.444 2.25 3.08 × 102 3.24 × 10-3

D

If the equilibrium constant for A + B C is 0.274, then the equilibrium constant for 2C 2A + 2B is 0.452 3.65 0.548 13.3 0.274

D

Which of the following is true about chemical equilibrium? Answers: It is microscopically and macroscopically static. It is microscopically and macroscopically dynamic. It is microscopically static and macroscopically dynamic. It is microscopically dynamic and macroscopically static. None of these are true about chemical equilibrium.

D

Consider the following system at equilibrium: N 2( g) + 3H 2( g) 2NH 3( g) + 92.94 kJ Which of the following changes will shift the equilibrium to the right? I. increasing the temperature II. decreasing the temperature III. increasing the volume IV. decreasing the volume V. removing some NH 3 VI. adding some NH 3 VII. removing some N 2 VIII. adding some N 2 Answers: I, IV, VI, VII II, III, V, VIII I, VI, VIII I, III, V, VII II, IV, V, VIII

E

If K = 0.154 for A 2 + 2B 2AB, then for 4AB 2A 2 + 4B, K would equal: Answers: 0.308 0.154 -0.154 3.25 42.2

E

Which of the following statements concerning equilibrium is not true? A system that is disturbed from an equilibrium condition responds in a manner to restore equilibrium. Equilibrium in molecular systems is dynamic, with two opposing processes balancing one another. The value of the equilibrium constant for a given reaction mixture is the same regardless of the direction from which equilibrium is attained. A system moves spontaneously toward a state of equilibrium. The equilibrium constant is independent of temperature.

E