CHEM 112 Equilibrium CHAPTER 15
Which of the following reactions will have the equilibrium constant expression KC = [C]2[A]3[C]2[A]3? Select all that apply.
3A(aq) + 2B(s) ⇄ 2C(aq) 3A(g) ⇄ 2B(s) + 2C(aq) 3A(g) + 2B(s) ⇄ 2C(aq)
reversible chemical process
3H2(g) + N2(g) ⇄ 2NH3(g)
Δn = -1
3O2(g) ⇌ 2O3(g)
In essence, a system at equilibrium wll respond to the addition of a species by _____ some of that species, and it will respond to the removal of a species by _____ more of that species
Consuming; producing
Increasing the temperature of an exothermic reaction causes the equilibrium constant to _____, shifting the equilibrium toward reactants
Decrease
Equilibrium is a _____ state- both forward and reverse reactions continue to occur, although there is no net change in reactant and product concentrations over time
Dynamics
A temperature increase favors an _____, and a temperature decrease favors an _____
Endothermic reaction; exothermic reaction
At a given temperature, the rate constants for the forward and reverse reaction remain _____ and the ratio kf/kt is equal to the _____ constant of rhte reaction
Equal; equilibrium
A system in which both forward and reverse processes are occurring at the same rate is at _____
Equilibrium
Kc is the...
Equilibrium constant
The value will change until the value of the reaction quotient equals that of the...
Equilibrium constant
KC > 1 × 10^2
Equilibrium favors the products; there will be higher concentrations or pressures of products than reactants at equilibrium.
KC < 1 × 10^-2
Equilibrium favors the reactants; there will be higher concentrations or pressures of reactants than products at equilibrium.
When the concentrations of all species are such that Qc is again equal to Kc, the system will have established a new _____, meaning that it will have shifted in one direction or the other, resulting in a new equilibrium concentration for each species
Equilibrium position
The quotient of product concentrations and reactant concentrations, each raise to the power of its stoichiometric coefficient
Equilibrum expression
Changing the way an equilibrium reaction is written will also change the equilibrium _____ and the equilibrium _____ for that reaction
Expression; constant
When the magnitude of Kc is very large, we expect the first outcome. A reaction with a very large equilbrium constant is sometimes said to "lie to the right or to "_____"
Favor products
Law of mass action
For a reversible reaction at equilibrium and a constant temperature, the reaction quotient Q, has a constant value, K
Increasing the temperature (adding heat) will shift the reaction in the _____
Forward direction
If the value of KC for the forward reaction is less than 1, the value of KC for the reverse reaction is _____ than 1.
Greater
Δn = 0
H2(g) + I2(g) ⇌ 2HI(g)
When the species in a reversible chemical reaction are not all in the same phase, the equilibrium is _____
Heterogeneous
Equilibria that are _____ have reacts and products that have all existed in the same phase- either gaseous or aqueous
Homogenous
Which of the following options correctly describes the units of Q and K for a reaction?
K and Q are dimensionless quantities.
Which of the following statements correctly describe the equilibrium constant K? Select all that apply.
K expresses a particular ratio of equilibrium concentrations of products and reactants. The value of K is characteristic of a particular equilibrium system. The expression for K has the general form [products]/[reactants]
2B(g) ⇄ 2A(g)
KC2=1(KC1)2
B(g) ⇄ A(g)
KC2=1KC1
3A(g) ⇄ 3B(g)
KC2=KC13
Which of the following equilibrium expressions are correct for the reaction, 2SO2(g) + O2(g) ⇄ 2SO3(g)? Choose all that apply.
KP = (PSO3)2(PSO2)2/(PO2)KC = [SO3]2[SO2]/2[O2]
Which of the following is the correct expression for the relationship between Kc and KP?
KP = Kc(RT)Δn(gas)
Equilibrium constant
Kc
For the reaction CO (g) + Cl2 (g) ⇌ COCl2 (g), Kp at 1000 K = 3.9 x 10-2. Which of the following options correctly reflect the steps required to calculate Kc at 1000 K? Select all that apply.
Kc = (3.9 x 10-2)(0.0821 x 1000)1 = 3.2 Δngas = -1
Which of the following correctly describes the relationship between the equilibrium constant K for a reaction and the rate constants for the forward and reverse reactions at equilibrium?
Kc = kf/kr
Generally speaking, an equilibrium constant with a magnitude greater than about 1 x 10^2 can be considered _____; one with a magnitude smaller than about 1 x 10^-2 can be considered _____
Large; small
Addition of a product or removal of a reactant will cause an equilibrium to shift to the...
Left
As a reaction proceeds, the value of Q _____.
increases or decreases, as necessary, until it reaches the value of K
irreversible chemical process
irreversible chemical process
You can determine the direction a reaction goes in by counting the number of moles on each side, counting only moles of gas. It will shift to whatever side has _____
Less
Initially, the forward process occurs at a higher rate than the reverse process, simply because of the...
Low number of ions in solution
Which of the following reactants and/or products would NOT appear in the expression for K for the following reaction? 4HCl (aq) + MnO2 (s) ⇌ MnCl2 (aq) + 2H2O (l) + Cl2 (g)
MnO2 H2O
An equilibrium that shifts to the right is one in which...
More products are produced
An equilibrium that shifts to the left is one in which...
More reactants are produced by the reverse reaction
An equilibrium constant that falls between 1 x 10^2 and 1 x 10^-2 indicates that...
Neither products nor reactants are strongly favored and that a system at equilibrium will contain a mixture of reactants AND products.
Original equation is multiplied by a number...
New constant is the original raised to the same number
Two equations are added
New constant is the product of the two original constants
Original equation is reversed...
New constant is the reciprocal of the original
Original equation is divided by 2
New constant is the square root of the original
In general, a decrease in volume of a reaction vessel will cause a shift in the equilibrium in the direction that minimizes the total number of _____. Conversely, an increase in volume will cause a shift in the direction that maximizes the toal number of moles of gas.
Number of moles
Which of the following starting mixtures would not be sufficient to establish chemical equilibrium for the following reaction? Choose all that apply. 2SO3(g) ⇄ 2SO2(g) + O2(g)
O2 only SO2 only
"Shifting" refers to the...
Occurence of either the forward or reverse reaction such that the effect of the stress is partially offset as the system establishes equilibrium
Equilibrium can be stablished starting with...
Only reactants, with only products, or with any mixture of reactants and products
When an equilibrium expression contains only gases, we can write an alternate form of the expression in which the concentrations of gases are expressed as _____ (atm).
Partial pressures
Select the correct expression for the equilibrium constant for the overall reaction when multiple chemical equations are added together.
koverall = k1 × k2 × k3 ×...
When constructing an equilibrium expression, which of the following states are not included?
liquids solids
reversible physical process
melting of ice at 0°C
Given the following data, what is the value of KP for the reaction at 545 K? 2NO2Cl (g) ⇌ 2NO (g) + Cl (g); Kc = 3.21 x 10-4 at 545 K
0.0144
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
Consider the following reactions: 2A(g) ⇄ 2B(g) + C(g); KC = 2.0 x 10-3 2B(g) ⇄ C(g) + D(g); KC= ? The value of KC for the overall reaction 2A(g) ⇄ 2C(g) + D(g) is KC = 5.0 x 107 What is the value of KC for 2B(g) ⇄ C(g) + D(g)?
2.5 x 10^10
If we combine stoichiometric amounts of the reactants in a reaction, what three outcomes are possible?
1. The reaction will go essentially to completion, and the equilibrium mixture will consist predominantly of products 2. The reaction will not occur to any significant degree, and the equilibrium mixture will consist predominantly of reactants and 3. The reaction will proced to a significant degree but will not go to completion, and the equilibrium mixture will contain comparable amounts of both reactants and products
Consider the equilibrium system 4A(g) + 2B(g) ⇄ 4C(g); KC1=47. What is the value of KC for the reaction 2A(g) + B(g) ⇄ 2C(g)?
6.9
It is possible to change the total pressure of a system without changing its volume- by...
Adding an inert gas such as helium to the reaction vessel. Because the total volume reamins the same, the concentrations of reactant and product gases do not change. Therefore, the equilibrium is not distrubed and no shift will occur.
Using Le Catelier's principle, we can predict the direction in which...
An equilibrium will shift, given the specific stress that is applied
A system in which the concentrations of reactants and products remain constant is said to be...
At equilibrium
Which of the following statements correctly describes a system at equilibrium for which KC = 1.2?
Both products and reactants are present in significant amounts at equilibrium.
1 × 10^-2 < KC < 1 × 10^2
Both reactants and products will be present in significant amounts at equilibrium.
Δn=1
CO2(s) ⇌ CO2(g)
To predict the direction in which a reaction will proceed when we start with a mixture of reactants ad products we...
Calculate the value of the reaction quotient, Qc, and compare it to the value of the equiligbrium constant, Kc.
The equilibrium constant, K, for a system at equilibrium expresses a particular ratio of equilibrium _____ of produts and reactants at a particular _____
Concentration; temeprature
The equilibrium constant K, Q is subscripted with a "c" to indicate that the quotient is definied in terms of...
Concentrations
If we know the equilibrium constant for a reaction, we can calculate the...
Concentrations in the equilibrium mixture from the initial reactant concentrations
To construct the expression for the equilibrium constant Kc for a given reaction, the _____concentrations are placed in the numerator and the _____ concentrations are placed in the denominator. Each term is then raised to the power of its stoichiometric coefficient from the _____ equation.
Product; reactant; balanced
Which of the following statements are correct about the reaction quotient, Q?
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.
Reaction quotient
Qc
The commparison of Q with K can refer to...
Qc and Kc or to Qp and Kp
The value of the equilibrium constant, KC, is a measure of how far the reaction proceeds toward the products at a given temperature. A small value of KC indicates that the reaction favors the ______, whereas a large value of KC indicates that the ______ will be present in a higher proportion.
Reactants; products
The _____ is a fraction with product concentrations in the numerator and reactant concentrations in the denominator- with each concentration raised to a power equal to the corresponding stoichiometric coefficient in the balanced chemical equation
Reaction quotient Qc
The addition or removal of a species from an equilibrium mixture does not changethe value of the equilibrium constant, K. Rather, it changes temporarily the value of the reaction quotient, Q. To cause a shift in the equilibrium, the species added or removed must be on that appears the in the _____
Reaction quotient expression
When reversing a reaction, because the equilibrium expression becomes the reciprocal of the orginal, the equilibrium constant is also the...
Reciprocal of the original
A double arrow indicates something is a _____, meaning that both the forward process and the reverse process can occur.
Reversible process
Addition of a reactant or the removal of a product will cause an equilibrium to shift to the...
Right
When the magnitude of Kc is very small, we expect the _____
Second outcome
If it is a _____ it is taken out of the expression because the ratio of moles to volume, which is how we definte the concentration, remains the same
Solid
The concentratinos of pure _____ and _____ are not included in the equilibrium expression fora given reaction
Solids; liquids
To calculate Qc we use the _____. To calculate Kc we must use _____
Starting concentrations; equilibrium concentrations
Le Chatelier's principle states that when a _____ is applied to a system at equilibrium, the system will respond by _____ in the direction that minimizes the effeect of the stress
Stress; shifting
Which of the following options correctly reflect the equation relating KP and Kc for a given reaction? Select all that apply.
T is the temperature in kelvin. R = 0.0821 atm⋅L/mol⋅K Δngas is determined from the coefficients of the balanced equation.
A change in concentration or volume may alter the position of an equilibrium (i.e., the relative amounts of reactants and products), but it does not change the value of an equilibrium constant. Only a change in _____ can alter the value of the equilibrium constant.
Temperature
One of the things the equilibrium constant tells us is the extent to which a reaction proceeds at a particular _____
Temperature
"Stress" refers to a disturbance of the system at equilibrium by any of the following means:
The addition of a reaction or product, the removal of a reactant or product, a change in concentration or partal pressure of the reactants and products, and a change in temperature
Why are pure liquids and solids not included in the equilibrium constant expression for a given reaction?
The concentrations of pure solids and liquids do not change appreciably as the reaction approaches equilibrium.
Choose all the statements that correctly describe equilibrium expressions for reactions containing only gases.
The equilibrium expression can be written in terms of the partial pressure of each gas in the reaction. The equilibrium expression can be written in terms of the concentration of each gas in the reaction.
Which of the following statements about equilibrium expressions and equilibrium constants are correct? Choose all that apply.
The equilibrium expression for a reaction involving only gases can be written in terms of either partial pressures or concentrations. A homogeneous equilibrium is one where all reactants and products are in the same physical state. When a chemical reaction is multiplied by a constant, the corresponding equilibrium expression is raised to the power of that constant.
Which of the following statements correctly describe a chemical system at equilibrium? Select all that apply.
The forward and reverse reactions occur at equal rates. There appears to be no visible change in the concentrations of reactants or products.
Q = K
The initial concentrations are equilibrium concentrations. The system is already at equilibrium, and there will be no net reaction in either direction
The value of KP for a given reaction is the equilibrium constant based on _____.
The partial pressures of the reactants and products
Which of the following statements correctly describe the rate equations for a system at equilibrium? Select all that apply. Multiple select question.
The rate of the forward reaction is equal to the rate of the reverse reaction. The ratio [products][reactants][products][reactants] remains constant although reactions continue to occur.
Q < K
The ratio of initial concentrations of products to reactants is too small. To reach equilibrium, reactants must be converted to products. The system proceeds in the forward direction (from left to right)
Q > K
The ratio of initial concentrations of products to reacts is too large. To reqach equilibrium, products must be converted to reactants. The system proceeds in the reverse direction (from right to left).
The law of mass action enables us to...
Write the equilibrium expression for any reaction for which we know the balanced equation. Knowing the equilibrium expression for a reaction, we can use equilibrium concentrations to calculate the value of the equilibrium constant.
3H2(g) + N2(g) ⇄ 2NH3(g)
condensation of steam at 95°C
Chemical equilibrium can be reached by starting with which of the following? Choose all that apply.
some of each reactant a mixture of reactants and products some of each product