SB ICE Tables, Q and LCP
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
If the temperature of a system at equilibrium is increased the system will shift to use up the excess heat, favoring the _____ reaction. A decrease in temperature causes more heat to be produced, favoring the _____ reaction.
endothermic, exothermic
Which of the following statements correctly describe how the addition of a catalyst will affect an equilibrium reaction? Select all that apply.
-A catalyst does not change the value of K. -A system will reach equilibrium more quickly in the presence of a catalyst.
Which of the following changes will cause the equilibrium shown to shift toward the products? Select all that apply.
-Add H2(g) without changing the volume. -Remove H2O(g) from the reaction vessel
Which of the following will change the total pressure in a reaction involving only gases at equilbrium?
-Changing the volume of the container -Adding or removing a reactant or product -Adding an inert gas
Which of the following correctly reflect ways in which a chemical equilibrium can be stressed? Select all that apply.
-Changing the volume of the reaction container for a reaction involving gases -Changing the concentrations of reactants or products -Changing the temperature of the system
Match the effect of each change described with the correct description of the resulting shift in equilibrium. Assume the system is at equilibrium before any change is made, and that all changes occur at constant temperature. -increase -double -add
-Equilibrium shifts toward the reactants. -Equilibrium shifts toward the products. -Equilibrium will be unaffected.
What will be observed if the temperature of the system is increased?
-Equilibrium will shift toward the reactants. -Kc will decrease.
What will be observed if the temperature of the system is decreased? Select all that apply.
-Equilibrium will shift toward the reactants. -The value of Kc will decrease. -The equilibrium concentration of H2O (g) will increase.
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 changes occur, and that the temperature remains constant throughout.
-H2(g) + Cl2(g) ⇄ 2HCl(g) -N2(g) + O2(g) ⇄ 2NO(g)
1.9 moles of HI are added to an evacuated, sealed 10.-L container and allowed to decompose according to the chemical equation:
-If the change in [H2] = +xH2 = +x, then at equilibrium [I2] = xI2 = x. -The initial [HI] = 0.19 MHI = 0.19 M. -Kc = 1.26 ×10−3 = (0.19 −2x)2 / x2
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.
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 the volume is decreased the reaction shifts in the direction that produces fewer moles of gas. -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.
For the reaction 2NO2Cl (g) ⇌ 2NO2 (g) + Cl2 (g), Kc = 3.21 × 10-4. If [NO2Cl] = 0.012 M, [NO2] = 0.018 M, and [Cl2] = 0.026 M, which of the following correctly reflect the steps required to determine the direction in which the reaction will proceed? Select all that apply.
-Qc = (0.026)(0.018)2 / (0.012)2 = 5.9 × 10-2 -Since Qc > Kc, the reaction will proceed toward the reactants.
The equilibrium constant for the reaction, A(g) ⇄ 2B(g), is kc = 2.7 × 10-12 and the initial reactant concentration is 0.5 M. Choose all of the statements that correctly describe how to determine the equilibrium concentrations of the reactant and product.
-The change in concentration of A is negligible compared to the original concentration. -kc = 2.7 × 10−12 = [B]2[A] = (2x)20.50kc = 2.7 × 10-12 = [B]2[A] = (2x)20.50 -The magnitude of kckc is very small and very little of A is used in the reaction.
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.
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.
Given the reaction 2NO2(g) ⇄ 2NO(g) + O2(g), what will be observed as the volume of the container is increased, assuming that temperature remains constant? Select all that apply.
-The concentrations of all species will decrease at the instant the volume is changed. -The equilibrium position will shift toward the products.
The equilibrium constant for the reaction, A(g) ⇄ 2B(g)A(g) ⇄ 2B(g), is kc = 2.7 × 10−12kc = 2.7 × 10-12 and the initial reactant concentration is 0.5 M. Choose all of the statements that correctly describe how to determine the equilibrium concentrations of the reactant and product.
-The magnitude of kckc is very small and very little of A is used in the reaction. -The change in concentration of A is negligible compared to the original concentration. -kc = 2.7 × 10−12 = [B]2 / [A] = (2x)2 / 0.50
Match each relationship between Q and K for a given reaction to the correct direction in which the reaction will proceed. -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.
What does the term "shift to the right" mean when describing the response of a system at equilibrium to a disturbance? Select all that apply.
-The reaction shifts toward the products until a new equilibrium state is established. -The concentrations of the products will increase until the system reaches equilibrium again.
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 QC and KC? 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.
Match the equilibrium expression with the strategy used to solve for x. -KC = 57 = (2x)2 / (0.25−x)(0.25−x) -KC = 5.9 × 10-10 = x / (0.24−x)(0.10−x) -KC = 23 = (2x)2 / (0.15−x)(0.18−x)
-There is.. -When K.. -When the..
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.
Place the steps for determining equilibrium concentrations from initial concentrations in the correct order.
-construct -tabulate -add -use
Match each of the following changes to the resulting effect on the pressure of an equilibrium system containing gaseous components. -increase in volume -adding gaseous reactant -adding an inert gas -adding a solid
-decrease -increase in pressure -increase in total pressue -no effect
Match each quantity with the correct description. -Kc -Qc
-expresses a particular ratio of product and reaction concentrations for a chemical system at equilibrium -expresses a particular ratio of product and reactant concentrations for a chemical system at any time
Consider the reaction, CaCO3(s) + 2HCl(aq) ⇄ CaCl2(aq) + CO2(g) + H2O(l). Which of the following changes will result in an increase in CO2(g) production? Choose all that apply.
-increase volume -increase concentration of HCl
For the exothermic reaction, CH4(g) + 2O2(g) ⇄ CO2(g) + 2H2O(g), match the effect of the applied stress on the equilibrium position. -increase in temperature -decrease in volume -addition of CH4(g)
-left -no -right
The equilibrium constant is a special value of the reaction _______ that occurs when reactant and product concentrations are at their _____ values.
-quotient -equilibrium
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
Which of the following is correct regarding catalysts and equilibrium?
Adding a catalyst to a reaction causes the reaction to reach equilibrium sooner.
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
At 100oC, KP = 60.6 for the chemical system 2NOBr (g) ⇌ 2NO (g) + Br2 (g). In an experiment, 0.10 atm of each gas is placed in a sealed container. In which direction will the reaction proceed?
The reaction will proceed toward the products.
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 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
As a reaction proceeds toward equilibrium from reactants to products (i.e., from left to right as written), the value of Q is _____.
increasing
A system at equilibrium will respond to a stress by a shift in equilibrium position. A "shift to the left" indicates that the reaction proceeds toward the _____, whereas a "shift to the right" indicates that the reaction proceeds toward the _____.
reactants, products
When Q < K, the reaction will proceed so that the concentrations of the _____ decrease and the concentrations of the _____ increase.
reactants; products
True or false: When the equilibrium constant for a reaction is much smaller than one, use of the quadratic formula is not necessary to solve for the equilibrium concentrations.
true
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.
volume
