Chemical Equilibrium, Activity, Law of Mass Action
What is the correct mass action expression for the equilibrium constant for this reaction written in terms of partial pressures: N2 (g) + 3H2 (g) ⇌ 2NH3 (g)
(PNH3)^2/(PN2)^1 x (PH2)^3
Gas activity equation
(PP/SP=1 atm)^coefficient
∆G°rxn=
-RTLnK
The reaction illustrated by the chemical equation below has come to equilibrium at a given temperature. The initial concentrations where 0.06 M SO2 and 0.05 M of O2. After equilibrium was reached, the concentration of SO3 was 0.04 M. What is the value of K? 2 SO2 (g) + O2 (g)
....
Kc for the following gas phase reaction is 4 at a certain temperature. A reaction is carried out at this temperature starting with 2 mole/L of CO and 2 mol/L of H2O. What will the equilibrium concentration be? CO (g) + H2O (g) ⇌ CO2 (g) + H2 (g)
.....
Elements in the standard state has a ∆G of
0
What is ∆G for spontaneous reactions?
0
Some nitrogen and hydrogen gases are pumped into an empty 5 L vessel at 500 degrees celsius. When equilibrium was established, 3 moles of N2, 2.10 moles of H2 and 0.298 moles of NH3 were present. Evaluate Kc.
0.07954 Remember n/v Kc= [NH3]^2/[N2] x [H2]^3 (0.298/5 L)^2/(3/5) x (2.10/5)^3= 0.07954
The system H2(g) + I2(g) ⇌ 2HI(g) is at equilibrium at a fixed temperature with a partial pressure of H2 of 0.200 atm, a partial pressure of I2 of 0.200 atm, and a partial pressure of HI of 0.100 atm. An additional 0.26 atm pressure of HI is admitted to the container, and it is allowed to come to equilibrium again. What is the new partial pressure of HI?
0.152 atm 1. Write all units given. PH2= 0.200 atm PI2= 0.200 atm HI= 0.100 atm + 0.26 atm 2. Write the Kp equation. (0.100)^2/(0.200)x(0.200) 3. Solve. 0.25 4. Add calculated pressure to initial concentration. 0.25 + 0.1= 0.35 atm 5. Write out RICE tables. Note that adding to the reactants
At 600°C, the equilibrium constant for the reaction 2HgO(s) ⟶ 2Hg(l) + O2(g) is 2.8. Calculate the equilibrium constant for the reaction 0.5O2(g) + Hg(l) ⟶ HgO(s).
0.60
Suppose the reaction H2(g) + I2(g) ⇌ 2HI(g) has an equilibrium constant Kc = 49 and the initial concentrations of H2 and I2 is 0.5 M and of HI is 0.0M. Which of the following is the correct value for the final concentration of HI(g)?
0.778 M
The system CO2(g) + H2(g) ⇌ H2O(g) + CO(g) is at equilibrium at some temperature. At equilibrium, a 4.00L vessel contains 1.00 mole CO2, 1.00 mole H2, 2.40 moles H2O, and 2.40 moles CO. How many moles of CO2 must be added to this system to bring the equilibrium CO concentration to 0.669 mol/L?
0.993 moles
What will the activities be for pure solids pure liquids?
1
Write the K equation for the reaction: Silver Nitrate reacts with Sodium chloride in water to produce silver chloride as a precipitate.
1. Write balanced equation with states. AgNO3 (aq) + NaCl (aq) -> AgCl (s) + NaNO3 (s) 2. Write net ionic equation. Ag+ (aq) + NO3- (aq) + Na+ (aq) + Cl- (aq) -> Na+ (aq) + NO3- (aq) 3. Cancel what stays the same. Ag+ (aq) + Cl- (aq) -> AgCl (s) 4. Write out K equation. K= 1/[Ag+][Cl-]
Kc = 2.6 x 10^8 at 825 K for the reaction 2H2(g) + S2(g) ⇌ 2H2S(g) The equilibrium concentration of H2 is 0.0020 M and S2 is 0.0010 M. What is the equilibrium concentration of H2S?
1.0 M 1. Write all units given. Kc= 2.6 x 10^8 T= 825 K H2= 0.0020 M S2= 0.0010 M 2. Write your Kc equation. Kc= [H2S]^2/[H2]^2[S2] 3. Plug in your concentration values. 2.6x10^8= x^2/(0.0020)^2 x (0.0010) 4. Isolate x. H2S= sqrt 2.6 x10^8 x (0.0020)^2 x (0.0010)= 1.0 M
At 990°C, Kc = 1.6 for the reaction H2(g) + CO2(g) ⇌ H2O(g) + CO(g) How many moles of H2O(g) are present in an equilibrium mixture resulting from the addition of 1.00 mole of H2, 2.00 moles of CO2, 0.75 moles of H2O, and 1.00 mole of CO to a 5.00 liter container at 990°C?
1.1 mol
If the equilibrium constant for this reaction N2 (g) + 3H2 (g) ⇌ 2NH3 (g) is K, what is the equilibrium constant for the following reaction? NH3 (g) ⇌ (1/2)N2 (g) + (3/2)H2 (g)
1/ sqrt K1
Consider the reaction: Cgraphite(s) + O2(g) CO2(g) ∆G° = -400 kJ Which of the following is a possible value of K for this reaction?
10^70
Calculate the equilibrium constant at 25°C for a reaction for which ΔG° = -4.22 kcal/mol.
1240.51
What is [H3O+] when [OH-] = 3.3 x 10-9 M?
3.0 x 10^-6 M
Consider the reaction below 2SO2(g) + O2(g) ⇌ 2SO3(g) At 1000 K the equilibrium pressures of the three gases in one mixture were found to be 0.562 atm SO2, 0.101 atm O2, and 0.332 atm SO3. Calculate the value of Kp for the reaction.
3.46
At a particular temperature you find the following reaction at equilibrium with the given concentrations of gases: 4HCl (g) + O2 (g) ⇌ 2H2O (g) + 2Cl2 (g) [HCl] = 0.1 M ; [O2] = 0.1 M ; [H2O] = 2 M ; [Cl2] = 0.1 M What is the value of Kc at this temperature?
4000
Consider the following reaction: 2NO(g) + Br2(g) ⇌ 2NOBr(g) Kp = 2.40 @ 373 K Calculate Kc for this reaction at 100°C.
73.5
According to the Bronsted-Lowry concept of acids and bases, which of the following statements about a base is NOT true? A. A base must contain a hydroxide group. B. If a base is strong, then its conjugate acid will be relatively weaker. C. A base reacts with an acid to form a salt. D. A base will share one of its electron pairs to bind H+.
A. A base must contain a hydroxide group. According to the Bronsted-Lowry defini- tion of bases, a base must be a proton accep- tor. It does not need to contain a hydroxide group.
The reaction A + B ⇌ C + 2D has an equilibrium constant of 3.7 x 10^-3. Consider a reaction mixture with: [A] = 2.0 x 10^-2 M [B] = 1.7 x 10^-4 M [C] = 2.4 x 10^-6 M [D] = 3.5 x 10^-3 M Which of the following statements is definitely true? A. The forward reaction will occur to a greater extent than the reverse reaction until equilibrium is established. B. The system is at equilibrium. C. The reverse reaction will occur to a greater extent than the forward reaction until equilibrium is established. D. No conclusions about the system can be made without additional information.
A. The forward reaction will occur to a greater extent than the reverse reaction until equilibrium is established.
Which of the following is true in pure water at any temperature? A. [H3O+] = [OH-] B. pH = 7.0 C. [H3O+][OH-] = 1.0 x 10-14 D. Kw decreases with increasing temperature.
A. [H3O+] = [OH-] Kw is shown to INCREASE with increas- ing temperature. pH = 7 is only true when water is at 24◦C. [H3O+][OH−] = Kw, which increases with temperature. At high temperatures pH can be less than 7. Thus [H3O+] = [OH−] is the only case that is true.
How does a system move towards equilibrium?
By producing more products or more reactants
an equilibrium constant of 3.7 x 10^-3. Consider a reaction mixture with: [A] = 2.0 x 10^-2 M [B] = 1.7 x 10^-4 M [C] = 2.4 x 10^-6 M [D] = 3.5 x 10^-3 M Which of the following statements is definitely true? A. The forward reaction will occur to a greater extent than the reverse reaction until equilibrium is established. B. The system is at equilibrium. C. The reverse reaction will occur to a greater extent than the forward reaction until equilibrium is established. D. No conclusions about the system can be made without additional information.
C. The reverse reaction will occur to a greater extent than the forward reaction until equilibrium is established.
Explain why equilibrium constants are dimensionless.
Every concentration or pressure that enters into Kc or Kp is really divided by the corresponding concentration or pressure of the substance in its standard state.
True or false: K does depend on the initial concentrations
False, does not depend
What is the net ionic equation for the chemical reaction between H2SO4 (aq) and NaOH (aq)?
H+ (aq) + OH- (aq) -> H2O (l)
In the reversible reaction HCN + H2O ⇌ CN- + H3O+, the two Bronsted-Lowry acids are...
HCN and H3O+
Strong Acids
HCl, HBr, HI, HClO3, HClO4, HNO3, H2SO4 dissociate in water
Le Chatelier's Principle
If a chemical system at equilibrium experiences a change, then the equilibrium shifts to counteract the imposed change and a new equilibrium is established.
∆G°rxn > 0 K __________ are favored at equilibrium
K<1 reactants are favored at equilibrium
Write the K equation for the reaction: 2 NH3 (g) + 3 CuO (s) -> N2 (g) + 3 H2O (l) + 3 Cu (s)
K= (PN2)/(PNH3)^2
∆G°rxn= 0 K ____________ favored at equilibrium
K= 1 neither favored at equilibrium
Write the K equation for the reaction: MgCO3 (s) -> MgO (s) + CO2 (g)
K= PCO2 1. Notice the state symbols. Use the state symbols to determine the K. Remember products/reactants. 1/1 x (PCO2) 2. Notice 1/1 will cancel leaving you with: K= PCO2
∆G°rxn < 0 K __________ are favored at equilibrium
K>1 products
For the following reaction what is the relationship between Kc and Kp? N2 (g) + 3H2 (g) ⇌ 2NH3 (g)
Kc = Kp(RT)^2
Consider the reaction 2HgO(s) ⇌ 2Hg(l) + O2(g) What is the form of the equilibrium constant Kc for this reaction?
Kc = O2
Kp=
Kc(RT)^∆n
Kc=
Kc= Kp(RT)^-∆n
Consider the reaction: Ni(CO)4(g) ⟶Ni(s) + 4CO(g) If the initial concentration of Ni(CO)4(g) is 1.0 M and x is the equilibrium concentration of CO(g), what is the correct equilibrium relation?
Kc= x^4/ (1 - x/4)
Write Kp for the reaction: CO (g) + H2O (l) ⇌ CO2 (g) + H2 (g)
Kp= (PCO/1 atm)^1 x (PH2/1 atm)^1/(PCO2/1 atm)^1 x 1
Strong Bases
LiOH, NaOH, KOH, RbOH, CsOH, Ca(OH)2, Sr(OH)2, Ba(OH)2, dissociate into ions in water
The reaction N2(g) + 3H2(g) ⇌ 2NH3(g) has an equilibrium constant of 4.0 x 10^8 at 25°C. What will eventually happen if 44.0 moles of NH3, 0.452 moles of N2, and 0.108 moles of H2 are put in a 10.0 L container at 25°.
More NH3 is formed 1. Write down all units. K= 4 x 10^8 T= 298 K nNH3= 44 nN2= 0.452 nH2= 0.108 V= 10 L 2. Calculate the molarity of all given using N/V. 44/10= 4.4 NH3 0.108/10= 0.0108 H2 0.452.10= 0.0452 N2 3. Plug molarity values into law of mass action equation. Remember products/reactants. (4.4)^2/(0.0108)^3 x (0.0452)= 3.4 x 10^8= Q 4. Compare your reaction quotient to your given K. 3.4 x 10^8 < 4 x 10^8 Q < K Products are favored/more stable, More NH3 will be formed.
What does a large K value tell us?
Most of the reactants are converted into products before equilibrium is established
Consider the following reactions at 25°C: 2NO(g) ⇌ N2(g) + O2(g) Kc = 1x10^30 2H2O(g) ⇌ 2H2(g) + O2(g) Kc = 5x10-^82 2CO(g) + O2(g) ⇌ 2CO2(g) Kc = 3x10^91 Which compound is most likely to dissociate and give O2(g) at 25°C?
NO
Given the hypothetical reaction: X(g) ⇌ Y(g) Predict what will happen when 1.0 mol Y is placed into an evacuated container.
Q will decrease until Q=K
H2 (g) + Br2 (g) ⇌ 2 HBr (g). At a certain temperature. The Kc is 25 and a reaction vessel contains a mixture with the following concentrations: H2= 0.2 M, Br2= 0.5 M, and HBr= 0.5. Is the system in equilibrium?
Q= (0.5)^2/(0.2)(0.5)= 5 Kc= 25 Q<K forward reaction is favored
At constant temperature, a reaction mixture will undergo a change in composition until:
Q=K
What will happen if you add products to an equation?
Reaction shift towards reactants, concentration of products will decrease
What will happen if you add reactants to an equation?
Reaction shifts towards products, concentration of reactants will decrease
True or false: Adding pure solids and pure liquids doesn't effect an equation's equilibrium according to Le Chateleir principle.
True
True or false: Every chemical process proceeds spontaneously toward equilibrium.
True
True or false: You can use Kc and Kp to calculate one another.
True
What is the correct mass action expression in terms of concentrations for the equilibrium constant of the given reaction: 3Cu (s) + 2NO3- (aq) + 8H+ (aq) ⇌ 3Cu2+ (aq) + 2NO (g) + 4H2O (l)
[NO]^2 x [Cu 2+]^3/[Cu]^3 x [NO3 -]^2 x [H+]^8
The expression for Kc for the reaction 4NH3(g) + 5O2(g) ⇌ 4NO(g) + 6H2O(g) at equilibrium is:
[NO]^4[H2O]^6/[NH3]^4[O2]^5
Activity
a function of the concentration or pressure of the substance that is used to measure the free energy of the substance as it is reference to the standard state
For the reaction below conducted at 400 degrees celsius, the equilibrium contstant, Kc= 1.99. The equilibrium concentrations are as follows [N2]= 0.014 M, [H2]= 0.172 M, and [NH3]= 0.0119 M. N2 (g) + 3 H2 (g) ⇌ 2NH3 (g) + 92 kJ. a) Calculate Kp at 400 degrees celsius. b) Calculate the pp of each gas in the equilibrium mixture.
a) Kp= Kc(RT)^∆n ∆n= 2-4= -2 1.99 x (0.0821 x 673)^-2= 6.5 x 10^-4 b) p=MRT PNH3= 0.0119 x 0.0821 x 673= 0.66 atm PN2= 0.014 x 0.0821 x 673= 0.77 atm PH2= 0.172 x 0.0821 x 673= 9.5 atm
K
activities of the products raised to the power of their coefficients/by the activities of the reactants raised to the power of the coefficient
Weak acids
an acid that is only slightly ionized in aqueous solution, written as using the neutral molecular formula
Law of Mass action
at equilibrium and a specific temperature express the composition of a reaction mixture in terms of the equilibrium constant
Dynamic equilibrium
both the forward and reverse reaction are occurring simultaneously at the same rate, so one can observe no net change in composition
Kc
concentration of gases without pressures
A solution reaches equilibrium when there is no further tendency for its composition to change. This is _________ ___________.
dynamic equilibrium
Q = K
equilibirum
True or False? At equilibrium, the reaction has stopped.
false
When a reaction is at equilibrium,
forward and reverse reactions occur at the same rate
Q < K
forward reaction ravored
Homogenous equilibria
involve reactants and products in the same phase
Heterogenous equilibria
involves species in more than one phase
What happens to the concentration of NO(g) when the total pressure on the equilib- rium reaction 3 N O 2 ( g ) + H 2 O ( l ) ⇀↽ 2 HNO3(aq) + NO(g) is increased (by compression)?
it increases
For composition of an ideal solution, the activity of each composition is the ratio of:
its molar concentration in relation to standard concentration which is 1 M
Equilibrium is the point at the __________ Gibbs free energy.
lowest
Consider the system: 2N2O5(g) ⇌ 2N2O4(g) + O2(g) at equilibrium at 25°C. If this is an exothermic reaction and the temperature was raised, would the equilibrium be shifted to produce more N2O5 or more N2O4?
more N2O5
∆G will be ________ if products are formed.
negative
When the chemical reaction A + B ⇌ C + D is at equilibrium, what is true?
neither the forward nor the reverse reactions have stopped
∆G= + Process is: ___________ favored:
non-spontaneous Reactants favored
You find the following reaction at equilibrium. What will happen if you remove some of the solid AgCl? Ag+ (aq) + Cl- (aq) ⇌ AgCl (s)
nothing
When the value of K is a number much greater than 1, we say that the reaction favors the _____________.
products
Q
reaction quotient refers to activities at any point in the process
Q > K
reverse reaction is favored
∆G= - Process is: ___________ favored:
spontaneous Products favored
Strong electrolytes
substances that completely dissociate into ions when they dissolve in water
∆G= 0 Process is: ___________ favored:
system is at equilibrium neither
K is only ___________ dependent.
temperature
Soluble ionic compounds
tend to be electrolytes
A water solution of sodium acetate is basic because...
the acetate ion acts as a Bronsted-Lowry base in a reaction with water.
The driving force behind spontaneous changes is
the lowering of free energy
When fully calculated, the mass action expression will equal this term no matter what conditions are present.
the reaction quotient, Q the current state of the system
You have the following reaction drug (aq) + protein (aq) ⇌ complex (aq) describing a drug binding to the active site in a protein. If this reaction is at equilibrium, what is the effect (if any) of diluting the entire mixture by adding more liquid water?
the reaction will shift to the left
The equilibrium constant for a reaction written in reverse is:
the reciprocal of Kc, the equilibrium constant for the original reaction 1/Kc
If the system does not have enough products,
the spontaneous change will be to produce more reactants and the reverse reaction is spontaneous
Consider the following reaction: 2SO2(g) + O2(g) ⇌ 2SO3(g) where ∆Hrxn = -198 kJ. The amount of SO2(g) at equilibrium increases when...
the volume is increased
What are the units for activity?
there are none, activities are unitless
Suppose the reaction mixture N2(g) + 3H2(g) ⇌ 2NH3(g) is at equilibrium at a given temperature and pressure. The pressure is then increased at constant temperature by compressing the reaction mixture, and the mixture is then allowed to reestablish equilibrium. At the new equilibrium...
there is more ammonia present than there was originally. 1. Look at moles of reactants vs moles of products. You have more moles of reactants than moles of products. 2. Remember that when pressure is added to a system, not only does the volume decrease, but the side with more moles will want to move in the direction of the side with less moles to reduce pressure. In this case, the side with less moles is Ammonia, so more ammonia will be created. LeChatelier's Principle states that if a change occurs in a system at equilibrium, the system responds to relieve the stress and reach a new equilibrium. Here, the number of moles of gaseous reactants is greater than the number of moles of products. Increasing the pressure of the above system will result in the reaction proceeding to reduce that pressure increase. The system will shift to the right (the side that has fewer moles of gas), so the pressure will be reduced; thus more ammonia will be produced.
For a reaction extra that involve ions in a solution you must:
write the equilibrium constant for the net ionic equation using activities of ions
∆Grxn= ∆G°rxn + RTLnQ
∆G°rxn + RTLnQ
