CH 17 Smart book part 2

Which of the following equilibrium calculations can be simplified by taking square roots on both sides of the equation? Select all that apply.

K = 420 = (0.1+x)(0.1+x)(2x)2 K = 0.15 = x2(0.1−x)(0.1−x)

When Q > K, the amount of the products must _____ and the amount of the reactants must _____ until equilibrium is established. The reaction will proceed toward the _____.

decrease; increase; reactants

Select the correct statement describing the effect of a catalyst on an equilibrium.

A catalyst has no effect on the equilibrium position.

Which of the following options correctly describe how a system at equilibrium will respond to a change in temperature? Select all that apply.

A change in temperature will cause a change in Kc. If the forward reaction is exothermic, an increase in temperature causes a shift to the left.

Which of the following will change the pressure in a reaction involving only gases at equilibrium? Select all that apply.

Adding or removing a reactant or product Changing the volume of the container Adding an inert gas

If Kc = 6.2 x 10-5 = x2(0.20-x)(0.15-x), which of the following options correctly describes the correct simplifying assumption made when solving for x?

Assume that x is small so that Kc ≈ x2(0.20)(0.15).

Which of the following correctly reflect ways in which a chemical equilibrium can be disturbed? Select all that apply.

Changing the volume of the reaction container for a reaction involving gases Changing the temperature of the system Changing the concentrations of reactants or products

Which of the following statements correctly describe how an equilibrium system containing gases will respond to changes in volume and/or pressure if the temperature remains unchanged? Select all that apply.

If an inert gas is added, there will be no effect on the equilibrium position. If the total number of moles of gas in the products and reactants is the same, a change in volume will not affect the equilibrium position. If the volume is decreased, the reaction shifts in the direction that produces fewer moles of gas.

1.9 moles of HI are added to an evacuated, sealed 10.-L reaction vessel and allowed to decompose according to the following reaction: H2 (g) + I2 (g) ⇌ 2 HI (g); Kc = 1.26 × 10−3 Which of the following options correctly reflect how to calculate [H2] at equilibrium? Select all that apply.

If the change in H2 = +x, then at equilibrium I2 = x. Kc = 1.26 × 10-3 = (0.19 - 2x)2x2 The initial HI = 0.19 M.

A 1-L flask containing 1.0 mol Br2, 1.0 mol Cl2, and 2.0 mol BrCl react according to the equation Br2 (g) + Cl2 (g) ⇌ 2BrCl (g); Kc = 7.0 at the reaction temperature. Select all the options that correctly interpret the data provided.

Kc = 7.0 =(2.0+2x)2(1.0-x)(1.0-x) The change in [Br2] will be -x.

Consider the equilibrium system C2H4 (g) + H2O (g) ⇌ C2H5OH (g); ΔHorxn = -47.8 kJ. What will be observed if the temperature of the system is increased? Select all that apply.

Kc will decrease. Equilibrium will shift toward the reactants.

A sample of solid C is placed in a sealed reaction vessel containing 2.0 atm H2 (g) and allowed to react according to the equation C (s) + 2H2 (g) ⇌ CH4 (g). At equilibrium the partial pressure of CH4 = 0.39 atm. Calculate Kp for the reaction.

Kp = 0.39(2.0-0.78)2 = 0.26

The Haber process is used to produce ammonia in industry. How does this process utilize Le Chatelier's principle to maximize reaction yields? The reaction is N2 (g) + 3H2 (g) ⇌ 2NH3 (g); ΔHorxn = -91.8 kJ.

Product is removed by condensation, so that the equilibrium continually shifts to the right to generate more product. The reaction is carried out at high pressures.

Based on Le Chatelier's principle, in what ways can we optimize production of ammonia from the Haber process? Select all that apply. The reaction is N2 (g) + 3H2 (g) ⇌ 2NH3 (g); ΔHorxn = -91.8 kJ.

Remove NH3 Add N2 and H2 Decrease the volume

Which of the following statements correctly explain why the addition of an inert gas to an equilibrium system involving gases does not cause a shift in the equilibrium position? Select all that apply.

The concentrations and the partial pressures of the gases involved in the reaction remain unchanged. The inert gas is not included in the expression for Q.

For the following reaction, what will be observed if the volume is increased at constant temperature? Select all that apply. 2NO2 (g) ⇌ 2NO (g) + O2 (g)

The concentrations of all species will decrease at the instant the volume is changed. The equilibrium position will shift toward the products.

Consider the equilibrium system C (s) + H2O (g) ⇌ CO (g) + H2 (g); ΔHorxn = 131 kJ. What will be observed if the temperature of the system is decreased? Select all that apply.

The equilibrium concentration of H2O (g) will increase. The equilibrium will shift toward the reactants. The value of Kc will decrease.

A 1-L flask contains 0.50 mol SO2Cl2, 0.30 mol SO2, and 0.16 mol Cl2, which react according to the equation SO2Cl2 (g) ⇌ SO2 (g) + Cl2 (g), Kc = 0.011 for the reaction temperature. Select all the options that correctly interpret the data provided.

The reaction will proceed toward the reactant. [SO2Cl2]eqm will be greater than 0.50 M. Kc = 0.011 =(0.30-x)(0.16-x)(0.50+x)

If the concentration of a reactant or product is changed in a system at equilibrium, what will happen to the value of K if the temperature remains constant?

The value of K will remain unchanged because the ratio of product to reactant concentration does not change.

An equilibrium calculation can be simplified by taking square roots on both sides of the equation when _____.

both numerator and denominator in the expression for K are perfect squares

If a system at equilibrium is disturbed by a change in concentration, the system will shift to _____ a substance that is added and to _____ a substance that has been removed.

consume; produce

If the temperature of a system at equilibrium is increased the system will shift to use up the excess heat, favoring a(n) _____ reaction. A decrease in temperature causes more heat to be produced, favoring a(n) _____ reaction.

endothermic; exothermic

If an equilibrium system contains gaseous reactants and/or products, a change in volume will cause a change in concentration and pressure. A decrease in volume will cause the system to shift in the direction that produces _____ moles of gas in total, whereas an increase in volume causes a shift in the direction that produces _____ moles of gas in total.

fewer; more

If a reaction has a relatively value of K and fairly initial concentrations, equilibrium calculations can be simplified by assuming that the change in concentration (x) is compared to [reactant]init. The assumption is justified as long as x is less than % of the initial concentration.

low high small five

The equilibrium constant expression for a particular reaction is given by Kc = (2x)2(0.1-x)(0.2-2x) . This equation cannot be simplified by taking square roots on both sides as the denominator is not a(n) square. In this case, the formula can be used to solve for x.

perfect quadratic

If a system at equilibrium is disturbed by changing the concentration of a reactant or product, the equilibrium will shift but the ratio of product to reactant will be once the system reestablishes equilibrium. The value of K will be .

position same unchanged

Three common ways of disturbing a system at equilibrium are to change the concentrations of reactants and/or products, the temperature, or the of the system.

pressure

If the temperature is increased for a system at equilibrium, an exothermic reaction (ΔH < 0) will shift toward the _____ and the value of K will _____. On the other hand, an endothermic reaction (ΔH > 0), will shift toward the _____ and the value of K will _____.

reactants; decrease; products; increase

Le Chatelier's principle states that when a chemical system at equilibrium is disturbed, the system will undergo a net reaction that the effect of the disturbance and will attain a new position.

reduces equilibrium

True or false: The quadratic formula is useful to find equilibrium concentrations when each must be represented by a different term in the equilibrium expression but two is the highest power of x.

t

The addition of an inert gas has no effect on the equilibrium position of a gaseous reaction because ______.

the partial pressures of the reaction components remain the same

N2O4 (g) ⇌ 2NO2 (g); Kc = 6.1 × 10-3 at 298 K If [N2O4] at the start of the reaction = 2.0 M, select ALL the options that correctly show how to calculate [NO2] at equilibrium. Assume that the change in [NO2] = +2x.

x = 2.8% of [N2O4]init so the simplifying assumption is justified. If the change in [NO2] = +2x then [N2O4]eqm = (2.0 - x). Kc = 6.1 × 10-3 ≈ 4x22.0

Given the following equilibrium data at a particular temperature: 2NO2Cl (g) ⇌ 2NO2 (g) + Cl2 (g) [NO2Cl] = 0.019 M, [NO2] = 0.041 M, and [Cl2] = 0.037 M calculate the value of Kc for the reaction at this temperature.

0.17

Calculate the equilibrium concentration of PCl3 for the equilibrium system represented below. PCl5 (g) ⇌ PCl3 (g) + Cl2 (g); Kc= 62; [PCl5] = 0.00582 M, and [Cl2] = 0.731 M.

0.49 M

Which of the following statements correctly describe how the addition of a catalyst will affect a system at equilibrium? Select all that apply.

A catalyst does not change the value of K. Equilibrium is unaffected.

0.20 mol of NO (g) is placed in a 1-L container with 0.15 mol of Br2 (g). These will react according to the balanced equation: 2NOBr (g) ⇌ 2NO (g) + Br2 (g). Given that [NOBr] = 0.18 M at equilibrium, select all the options that correctly describe the steps required to calculate Kc for the reaction.

x = 0.182 = 0.09 If the change in [Br2] = -x, then the change in [NOBr] = +2x. The initial [NOBr] = 0 M.

Which of the following statements correctly describe how a system at equilibrium will respond to a change in concentration of any species that appears in the expressions for Q and K? Select all that apply.

The value of Kc is not affected by changes in concentration. If a reactant is removed from the system, the equilibrium will shift toward the reactants. If a reacting substance is added, the equilibrium position will shift to use up the substance.

Which of the following options correctly describe the van't Hoff equation? Select all that apply.

The value of R used in this equation is 8.314 J/mol⋅K. The units of ΔHorxn must be consistent with the units of R when using this equation. The van't Hoff equation expresses the change in equilibrium constant as temperature changes.

Which of the following statements correctly reflect Le Chatelier's principle? Select all that apply.

When a system at equilibrium is disturbed, the system reacts to minimize the effect of the disturbance. When a system at equilibrium is disturbed, Q ≠ K.

Select the correct form of the van't Hoff equation that relates the change in the equilibrium constant to a change in temperature.

lnK2K1 = ΔHrxnR1T1-1T2