Gen. Chem II Chapter 17
Given the following reaction, which concentration terms appear in the denominator of the expressions for Qc and Kc? Select all that apply. CFCl3 (g) + HCl (g) ⇌ CCl4 (g) + HF (g)
[HCl] [CFCl3]
Given the balanced equation 2NO2 (g) ⇌ 2NO (g) + O2 (g), what is the expression for K for the reverse reaction?
[NO2]^2 / [NO]^2[O2]
What is the correct expression for Qc for the reaction 2POCl3 (g) ⇌ 2PCl3 (g) + O2 (g)?
[PCl3]^2[O2] / [POCl3]^2
For a given reaction, Kc is the equilibrium constant based on the molar__________ of reactants and products while Kp is the equilibrium constant based on the partial__________ of reactants and products.
concentration, pressures
The subscript "c" used in the symbols Qc and Kc indicates that these quantities are based on the of products and reactants.
concentrations
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
Which of the following options correctly describe the equilibrium constant K? Select all that apply.
+K = kfwd/krev for a system at equilibrium. +The value of K is characteristic of a particular equilibrium system. +K expresses a particular ratio of equilibrium concentrations of products and reactants.
Which of the following types of reactants and products do not appear in a reaction quotient expression for a heterogeneous reaction? Select all that apply.
+Pure solids +Pure liquids
Match each quantity with the correct description. K Q
+expresses a particular ratio of product and reactant concentrations for a reaction at equilibrium. +expresses a particular ratio of product and reactant concentrations for a reaction at any time.
Given the balanced equation 2PbO (s) + O2 (g) ⇌ 2PbO2 (s), calculate the value of Δngas.
-1
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
Given the reaction 2NO2 (g) ⇌ 2NO (g) + O2 (g); K = 1.1 x 10-5, what is the value of K for the reaction 2NO (g) + O2 (g) ⇌ 2NO2 (g)?
9.1 x 10^4 Reason: Krev = 1/K(fwd)=1.1×10^-5
Which of the following will change the pressure in a reaction involving only gases at equilibrium? Select all that apply.
Adding an inert gas Changing the volume of the container Adding or removing a reactant or product
If Kc = 6.2 x 10-5 = x2(0.20-x)(0.15-x)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 ≈ x^2 / (0.20)(0.15)
0.45 mol PCl5 (g) is placed in a sealed 2.0-L container and reacts according to the equation: PCl5 (g) ⇌ PCl3 (g) + Cl2 (g). If [Cl2] = 0.10 M at equilibrium, select all the options that correctly reflect the steps required to calculate Kc.
At equilibrium [PCl3] = 0.10 M. Kc = (0.10)(0.10) / (0.13) The initial [PCl5] = 0.23 M.
A reaction is started with 2.8 M H2 (g) and 1.6 M I2 (g). Fill in the reaction table below correctly in order to calculate the value of Kc for the reaction H2 (g) + I2 (g) ⇌ 2HI (g). (Do not put any spaces between signs and numbers in your answers, and do NOT include any units or parentheses.) A is B is C is D is
Blank 1: 2x or +2x Blank 2: 2.8 - x, 2.8-x, or 2.8 -x Blank 3: 1.6-x, 1.6 - x, or 1.6 -x Blank 4: 2x, 0+2x, 0 + 2x, or +2x
Which of the following statements correctly describes a system at equilibrium for which K = 1.2?
Both products and reactants are present in significant amounts at equilibrium. (Reason: When the equilibrium constant is close to 1, there are comparable concentrations of products and reactants.)
Which of the following reactions will not undergo a shift in equilibrium position when the volume or pressure changes? Select all that apply.
Cl2 (g) + Br2 (g) ⇌ 2BrCl (g) 4CuO (s) + CH4 (g) ⇌ 4Cu (s) + H2O (l) + CO2 (g)
The equilibrium constant K for a system at equilibrium expresses a particular ratio of equilibrium ________ of products and reactants at a particular __________ . The value of K is also equal to the ratio of the rate __________ for the forward and reverse reactions.
Concentrations, temperature, constants
Which of the following statements correctly describe how the addition of a catalyst will affect a system at equilibrium? Select all that apply.
Equilibrium is unaffected. A catalyst does not change the value of K.
Increase the volume of the container Double the partial pressures of all species Add 1 mol of Ne (g)
Equilibrium shifts toward the reactants. Equilibrium shifts toward the products. Equilibrium will be unaffected.
Which of the following reactions will not undergo a shift in equilibrium position when the volume or pressure changes? Select all that apply. Assume that each system is at equilibrium before the changes occur and that the temperature remains constant throughout.
H2 (g) + Cl2 (g) ⇌ 2HCl (g) N2 (g) + O2 (g) ⇌ 2NO (g)
Δngas = 0 Δngas = -1 Δngas = 1
H2 (g) + I2 (g) ⇌ 2HI (g) 3O2 (g) ⇌ 2O3 (g) CO2 (s) ⇌ CO2 (g)
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.
If a reacting substance is added, the equilibrium position will shift to use up the substance. 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.
Which of the following options correctly describe how a system at equilibrium will respond to a change in temperature? Select all that apply.
If the forward reaction is exothermic, an increase in temperature causes a shift to the left. A change in temperature will cause a change in Kc.
Select the new equilibrium constant, K', of a reaction multiplied by a factor n, that is n(aA + bB ⇌ cC + dD).
K' = Kn
How does the equilibrium constant change when all the coefficients of a balanced equation are multiplied by the same factor?
K' = Kn, where n is the factor by which the coefficients are multiplied.
0.50 mol of SO3 (g) is placed in a sealed 1-L container at 700°C and reacts according to the equation: 2SO3 (g) ⇌ 2SO2 (g) + O2 (g). If [O2] at equilibrium = 0.15 M, which of the following gives the correct calculation for Kc?
Kc = (0.15)(0.30)^2 / (0.20)^2 = 0.34
0.50 mol of SO3 (g) is placed in a sealed 1-L container at 700°C and reacts according to the equation: 2SO3 (g) ⇌ 2SO2 (g) + O2 (g). If [O2] at equilibrium = 0.15 M, which of the following gives the correct calculation for Kc?
Kc = (0.15)(0.30)^2 / (0.20)^2= 0.34
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.
Kc = 0.011 =(0.30-x)(0.16-x) / (0.50+x) The reaction will proceed toward the reactant. [SO2Cl2]eqm will be greater than 0.50 M.
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.
Kc = 6.1 × 10-3 ≈ 4x^2 / 2.0 If the change in [NO2] = +2x then [N2O4]eqm = (2.0 - x). x = 2.8% of [N2O4]init so the simplifying assumption is justified.
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
Which of the following symbols for Q denote the reaction quotient based on molar concentrations?
Qc
The equilibrium constant is a special value of the reaction ________ that occurs when reactant and product concentrations are at their________ values.
Quotient, equilibrium
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.
Reason: Kc = (0.041)^2(0.037) / (0.019)^2 = 0.17
Which of the following changes will cause the equilibrium shown to shift toward the products? Select all that apply. Fe3O4 (s) + 4H2 (g) ⇌ 3Fe (s) + 4H2O (g)
Remove H2O (g) from the reaction vessel Add H2 (g) without changing the volume.
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.
The change in [Br2] will be -x. Kc = 7.0 =(2.0+2x)^2(1.0-x)(1.0-x)
If O2 (g) is added to the equilibrium system 2NO (g) ⇌ N2 (g) + O2 (g), which of the following will be observed? Select all that apply.
The concentration of NO will increase. The reaction will shift to the left.
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 will shift toward the reactants. The equilibrium concentration of H2O (g) will increase. The value of Kc will decrease.
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 × 10−3H2 (g) + I2 (g) ⇌ 2 HI (g); Kc = 1.26 × 10-3 Which of the following options correctly reflect how to calculate [H2]H2 at equilibrium? Select all that apply.
The initial [HI] = 0.19 M Kc = 1.26 × 10^−3 = (0.19 − 2x)^2 / x2 If the change in [H2] = +x, then at equilibrium [I2] =x
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.
The initial [NOBr] = 0 M. If the change in [Br2] = -x, then the change in [NOBr] = +2x. x = 0.1820.182 = 0.09
In a given experiment, 0.10 atm of each component in the following reaction is placed in a sealed container. In which direction will the reaction proceed? 2NOBr (g) ⇌ 2NO (g) + Br2 (g) where KP = 60.6 at 100°C
The reaction proceeds toward the products.
If O2 (g) is added to the equilibrium system 2NO (g) ⇌ N2 (g) + O2 (g), which of the following will be observed? Select all that apply.
The reaction will shift to the left. The concentration of NO will increase.
If the equilibrium constant K for a particular reaction is 1.22 x 1014, which of the following statements correctly describes the reaction?
There are large concentrations of products compared to reactants.
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.
Given the following reaction, which concentration terms appear in the denominator of the expressions for Qc and Kc? Select all that apply. CFCl3 (g) + HCl (g) ⇌ CCl4 (g) + HF (g)
[CFCl3] [HCl]
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 the value of K for the forward reaction is less than 1, the value of K for the reverse reaction is _____ than 1.
greater
If the value of K for the forward reaction is less than 1, the value of K for the reverse reaction is _____ than 1.
greater (Reason: The value of K for the forward reaction is the reciprocal of the value of K for the reverse reaction.)
As a reaction proceeds, the value of Q _____.
increases or decreases, as necessary, until it reaches the value of K
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; 5
For a balanced chemical equation that has been multiplied by some factor x, the corresponding reaction quotient (or equilibrium constant) must be ______ that same factor.
raised to a power of
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
The concentrations of pure ________ and _________are not included in the expression for Q or K for a given heterogeneous reaction.
solids; liquids
The value of Kp for a given reaction is the equilibrium constant based on _____.
the partial pressures of the reactants and products
The value of K for the forward reaction is _____ the value of K for the reverse reaction.
the reciprocal of
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 statements about the reaction quotient Q are correct? Select all that apply.
+Q expresses a particular ratio of products and reactants at any time during a reaction. +Q = K only at equilibrium. The expression for Q is the same as the expression for K.
Select all the options that correctly reflect the steps required to determine the direction in which the following reaction will proceed at the given concentrations 2NO2Cl (g) ⇌ 2NO2 (g) + Cl2 (g), where Kc = 3.21 × 10-4 if [NO2Cl] = 0.012 M, [NO2] = 0.018 M, and [Cl2] = 0.026 M.
+Qc = (0.026)(0.018)^2 / (0.012)^2= 5.9 × 10^-2 +Since Qc > Kc, the reaction will proceed toward the reactants.
Which of the following statements about the reaction quotient Q are correct? Select all that apply.
+The expression for Q is the same as the expression for K. +Q expresses a particular ratio of products and reactants at any time during a reaction. +Q = K only at equilibrium.
Q<K Q=K Q>K
+The reaction proceeds toward the products. +The system is at equilibrium, and no further net change occurs. +The reaction proceeds toward the reactants.
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
Increase in volume Adding a gaseous reactant Adding an inert gas Adding a solid
decrease in pressure increase in pressure increase in total pressure, but no change in partial pressures of gases no effect on pressure