AP Chem Equilibrium

For the decomposition of A to B and C, A(s)⇌B(g)+C(g) how will the reaction respond to each of the following changes at equilibrium?

- Leftward shift: Double the concentrations of both products. - No shift: Add more A. Double the concentrations of both products then double the container volume. Double the concentration of B and halve the concentration of C. - Rightward shift: Double the container volume. Double the concentrations of both products and then quadruple the container volume.

For the reaction of A and B forming C, A(g)+B(s)⇌2C(g) how will the reaction respond to each of the following changes at equilibrium?

- Leftward shift: Halve the concentration of A. Double the concentrations of A and C. - No shift: Quadruple the number of moles of B. - Rightward shift: Halve the concentration of C. Double the concentration of A.

What happens to a gaseous system immediately after an increase in container size?

- it will decrease in concentrations of all species and decrease pressure of all species

Phosgene (carbonyl chloride), COCl2, is an extremely toxic gas that is used in manufacturing certain dyes and plastics. Phosgene can be produced by reacting carbon monoxide and chlorine gas at high temperatures: CO(g)+Cl2(g)⇌COCl2(g) Carbon monoxide and chlorine gas are allowed to react in a sealed vessel at 463 ∘C . At equilibrium, the concentrations were measured and the following results obtained: Gas Partial Pressure (atm) CO 0.790 Cl2 1.18 COCl2 0.210 What is the equilibrium constant, Kp, of this reaction?

.255 bc Kp= .210/(1.18)(.790)

What are the equilibrium partial pressures of PCl3 , Cl2, and PCl5, respectively?

.726, .726, .074 Kp = (PCl5) / (PCl3) (Cl2) 0.140 = (0.300+X) / (0.500-X) (0.500-X) 0.140 = (0.300+X) / (0.250 - X + X^2) *solve for X* X = -0.226174 (this is the only reasonable root) so PCL3 = 0.500-(-0.226) = 0.726 atm Cl2 is the same = 0.726 atm PCl5 = 0.300 + (-0.226) = 0.074 atm

For the exothermic reaction PCl3(g)+Cl2(g)⇌PCl5(g) Kp = 0.140 at a certain temperature. A flask is charged with 0.500 atm PCl3 , 0.500 atm Cl2, and 0.300 atm PCl5 at this temperature. True or False 1. Q is less than K == F 2. The reaction is at equilibrium == F 3. Q is greater than K ==T 4. Q is equal to K == F 5. The net reaction proceeds to the left to attain equilibrium == T 6. No net reaction will occur == F 7. The net reaction proceeds to the right to attain equilibrium == F

1) false 2) false 3) true 4)false 5)true 6)false 7)false

EXTRA facts

1. If you reverse the equation, invert the equilibrium constant. 2. If you multiply the coefficients in the equation by a factor, raise the equilibrium constant to the same factor. 3. If you add two or more individual chemical equations to obtain an overall equation, multiply the corresponding equilibrium constants by each other to obtain the overall equilibrium constant. The concentration of a solid or a pure liquid is constant as long as some of the pure substance is present since concentration depends only on density. Changing the volume of the container does not affect a reaction when the number of moles of gaseous product is the same as the number of moles of gaseous reactants. True statements: Increasing the temperature causes an exothermic reaction to produce more reactants. Decreasing the temperature causes an exothermic reaction to produce more products. Increasing the temperature of an endothermic reaction increases the equilibrium constant.

The following reaction was carried out in a 2.00 L reaction vessel at 1100 K: C(s)+H2O(g)⇌CO(g)+H2(g) If during the course of the reaction, the vessel is found to contain 5.00 mol of C, 12.6 mol of H2O, 4.00 mol of CO, and 7.70 mol of H2, what is the reaction quotient Q? Enter the reaction quotient numerically.

1.22 Get the mols of each and find its molar concentration (mol/liter) and then plug that into Q= (CO) (H2) / (H2O) to find the answer

The following reaction was performed in a sealed vessel at 755 ∘C : H2(g)+I2(g)⇌2HI(g) Initially, only H2 and I2 were present at concentrations of [H2]=3.30M and [I2]=2.10M. The equilibrium concentration of I2 is 0.0900 M . What is the equilibrium constant, Kc, for the reaction at this temperature? Express your answer numerically.

139 R: H2 (g) + I2(g) <-> 2HI I: 3.30 2.10 0 C: -X -X +2X E: 3.30-X 2.10-X 2X *already know that equilibrium concentration is 0.0900 M** 2.10 -x = 0.900 (use algebra to find x) x= 2.01 **use X to find all the other equilibrium concentrations, plug them into the equilibrium concentration equation to get 139**

A chemical reaction between X2 (red) and Y2 (blue) produces XY (red-blue). All species are in a gaseous state. The picture shown here represents the equilibrium mixture. Calculate the equilibrium constant for the balanced reaction between one mole of each reagent.

2.72 3 red atoms 7 red/blue Kc= Products/Reactants A2+B2 <-> 2AB (balanced) Kc=7^2/(3*6) = 49/18 = 2.72 Squared the 7 because it means you're going to multiply the 7 reds in the red/blue atoms by the 7 blues in the red/blue atoms, giving you 49. And then you divide it by the 3 individual blues multiplied by the 6 individual reds, giving you 18. 49 divided by 18 is 2.72.

At a certain temperature the initial concentration of NO was 0.400 M and that of Br2 was 0.255 M . At equilibrium the concentration of NOBr was found to be 0.250 M. What is the value of Kc at this temperature?

21.37 0.250 moles NOBr x 2 moles NO/ 2 molesNOBr = 0.250 moles NO react 0.250 moles NOBr x 1 mole Br/ 2 moles NOBr = 0.125 moles Br2 react moles of NO that are present at equilibrium: 0.400 - 0.250 = 0.150 moles of Br2 that are present at equilibrium: 0.255 - 0.125 = 0.140 All are present in 1.0 liter Kc = [NOBr]^2 / [NO]^2[Br2] Kc = (0.250)^2 / (0.150)^2( 0.140) Kc = 21.37

The equilibrium-constant of the reaction NO2(g)+NO3(g)⇌N2O5(g) is K=2.1×10^−20. What can be said about this reaction? Where does the equilibrium of this reaction lie?

At equilibrium the concentration of reactants is much greater than that of products. * if the concentrations of products are relatively large at equilibrium compared to the concentrations of reactants, the numerator of the equilibrium-constant expression will be quite large compared to the denominator, and the value of K will be correspondingly large.* Far to the left **Recall that if products are favored, the equilibrium is said to lie to the right, since more of the chemical species from the right-hand side of the equation are at equilibrium. Similarly, if reactants are favored, the equilibrium is said to lie to the left, since more of the chemical species from the left-hand side of the equation will be present at equilibrium.**

What is the value of Kc for the decomposition of HI at 623 K?

I2 + 2Na2(S2O3) → Na2(S4O6) + 2NaI (28.68ml)(0.015 mmol/ml) = 0.4303 mmol [S2O3]^2- consumed Therefore, there were 0.4303/2 mmol = 0.2151 mmol I2 present initial 0.280g HI = 280mg/(127.91 mg/mmol) = 2.189 mmol .....2HI(g) ⇌ H2(g) + I2(g) 2.189-2x........x.........x Therefore, final HI = 2.189 -2(0.2151) mmol Kc = (0.2151)^2/(2.189 - 2(0.2151))^2 = 0.01496 Since the # of moles of reactants and products are equal, the volume of the bulb isn't needed (it cancels out of Kc). For the same reason Kc = Kp

Le Châtelier's principle states that

If a stress is applied to a reaction mixture at equilibrium, a net reaction occurs in the direction that relieves the stress.

Determine the value of the equilibrium constant, Kgoal, for the reaction N2(g)+O2(g)+H2(g)⇌12N2H4(g)+NO2(g), Kgoal=? by making use of the following information: 1. N2(g)+O2(g)⇌2NO(g), K1 = 4.10×10^−31 2. N2(g)+2H2(g)⇌N2H4(g), K2 = 7.40×10^−26 3. 2NO(g)+O2(g)⇌2NO2(g), K3 = 6.00×10^−13

K = 1.35e-34 K= (K1 * K2 * K3)^1/2

Determine the equilibrium constant, Kgoal, for the reaction 4PCl5(g)⇌P4(s)+10Cl2(g), Kgoal=? by making use of the following information: P4(s)+6Cl2(g)⇌4PCl3(g), K1=2.00×10^19 PCl5(g)⇌PCl3(g)+Cl2(g), K2=1.13×10^−2

K = 8.15e-28 Kgoal=1K1×(K2)^4

The acid HOCl (hypochlorous acid) is produced by bubbling chlorine gas through a suspension of solid mercury(II) oxide particles in liquid water according to the equation 2HgO(s)+H2O(l)+2Cl2(g)⇌2HOCl(aq)+HgO⋅HgCl2(s) What is the equilibrium-constant expression for this reaction?

K=[HOCl]2/[Cl2]2 exclude everything else bc those are pure solids and liquids

Hydrogen is used as a rocket fuel because it is very light and reacts explosively and completely with oxygen. For the combustion reaction 2H2(g)+O2(g)⇌2H2O(g) what is the likely magnitude of the equilibrium constant K?

K> 10^3 B/c when K>1, the products are favored

What is the equilibrium constant

Kc

A mixture initially contains A, B, and C in the following concentrations: [A] = 0.300 M , [B] = 1.40 M , and [C] = 0.700 M . The following reaction occurs and equilibrium is established: A+2B⇌C At equilibrium, [A] = 0.120 M and [C] = 0.880 M . Calculate the value of the equilibrium constant, Kc.

Kc = 6.78

concentrations in an equilibrium mixture are related by the equilibrium equation:

Kc=[C]^c[D]^d/[A]^a[B]^b

or a gaseous reaction with the general form aA+bB⇌cC+dD how would you write Kc and Kp

Kc=[C]^c[D]^d/[A]^a[B]^b Kp=(PC)^c(PD)^d/(PA)^a(PB)^b

At this temperature the rate constant for the reverse reaction is 360. M−1s−1 . What is kf for the reaction?

Kf =7690 Kc = Kf/Kr 21.37 = Kf/360 (use algebra) Kf = 7693.2

For the reaction aA+bB⇌cC+dD, what is the quotient expression?

Q=[C]^c[D]^d/[A]^a[B]^b

What is the relationship between Kc and Qc

Qc > Kc

What will happen when Qc>Kc?

Qc will decrease until it is equal to Kc.

What is the (reaction quotient) equation used if the reaction is NOT at equilibrium

Qc=[C]t^c[D]t^d/A]t^a[B]t^b *t is time that will be given*

What is the rate of the reaction when the initial concentration of NO is 0.400 M and that of Br2 is 0.255 M ?

Rate 314 Rate = Kf/[NO]^2 * [Br2] Rate = 7693.2/ [.400]^2 * [.255] Rate = 313.88256

For the reaction HCONH2(g)⇌NH3(g)+CO(g), K= 4.84 at 400 K what can be said about this reaction at this temperature?

The reaction contains significant amounts of products and reactants at equilibrium. **when 10^−3<K<10^3, the reaction is considered to contain a significant amount of both reactants and products at equilibrium.**

Ammonia can be produced via the chemical reaction N2(g)+3H2(g)⇌2NH3(g) During the production process, the production engineer determines the reaction quotient to be Q = 3.56×10−4. If K = 6.02×10−2, what can be said about the reaction?

The reaction is not at equilibrium and will proceed to the right. *If Q is less than K, the ratio of products to reactants is smaller than at equilibrium. In this case, the reaction will proceed to the right to create more product and reach equilibrium. Conversely, if Q is greater than K, the ratio of products to reactants is larger than at equilibrium. In this case, the reaction will proceed to the left and revert some of the product back to reactants to reach equilibrium.

Chemical equilibrium

The reaction state when the concentrations of reactants and products remain constant over time. The reaction does not stop, but it reaches a dynamic equilibrium when the rates of the forward and reverse reactions become equal.

Now consider the reaction A+2B⇌C for which in the initial mixture Qc=[C]/[A][B]^2=387 Is the reaction at equilibrium? If not, in which direction will it proceed to reach equilibrium?

The reaction will proceed in reverse to form reactants.

equilibrium mixture

a mixture of reactants and products in the equilibrium state

Bulb Initial mass of HI (g) Time (hours) Volume of titrant (mL) 1 0.300 2 20.96 2 0.320 4 27.90 3 0.315 12 32.31 4 0.406 20 41.50 5 0.280 40 28.68 In which bulb would you expect the composition of gases to be closest to equilibrium?

bulb 5 find Q

As the rate of the forward reaction begins to __________ , and the rate of the reverse reaction begins to ___________.

decrease, increase

when a system produces reactants, Q is _________ than K

greater - produces reactants while consuming products (thus decreasing Q to match K)

An increase in temperature will cause the reaction to shift toward the side with

higher enthalpy

How will the following changes affect the mole fraction of chlorine gas, χCl2, in the equilibrium mixture.

increase χCl2: increasing temp, increasing volume decreasing χCl2: decreasing temp, decreasing volume

rate constant for forward rate

kf

rate of constant for reverse rate

kr

For the following systems at equilibrium A : 2NOCl(g) ⇌ 2NO(g) + Cl2(g) B : H2(g) + I2(g) ⇌ 2HI(g) classify these changes by their effect.

leftward shift - system A decrease container size no shift -system B increase container size -system B decrease container size rightward shift -system A increase container size

Part A Consider the following system at equilibrium: A(aq)+B(aq)⇌2C(aq) Classify each of the following actions by whether it causes a leftward shift, a rightward shift, or no shift in the direction of the net reaction. Drag the appropriate items to their respective bins.

leftward shift: decrease A, increase C, decrease B, Double both B and C rightward shift: increase A, decrease C, increase B, no shift: Double A and halve B (they cancel each other out)

The following system is at equilibrium: A(s)+4B(g)⇌C(g) Classify each of the following actions by whether it causes a leftward shift, a rightward shift, or no shift in the direction of the net reaction.

leftward shift: double the volume rightward shift: halve the volume no shift: remove some A and add more A

For the reaction N2(g)+O2(g)⇌2NO(g) classify each of the following actions by whether it causes a leftward shift, a rightward shift, or no shift in the direction of the reaction. Drag the appropriate items to their respective bins.

leftward shift: halve nitrogen, halve oxygen, and halve carbon monoxide no shift: n/a rightward shift: double oxygen, double nitrogen, double carbon monoxide

For the following systems at equilibrium C:D:CaCO3(s)PCl3(g)+Cl2(g)⇌⇌CaO(s)+CO2(g)PCl5(g)ΔH=+178 kJ/molΔH=−88 kJ/mol classify these changes by their effect. Drag the appropriate items to their respective bins.

leftward shift: system C temp decrease, system D temp increase no shift rightward shift: system C temp increase, system D temp decrease

For a certain chemical reaction, ΔH∘=−156kJ. Assuming the reaction is at equilibrium, classify each of the following actions by whether it causes a leftward shift, a rightward shift, or no shift in the direction of the net reaction. Drag the appropriate items to their respective bins.

leftward: increase temp rightward: decrease temp * - delta H means exo (A <-> B +heat)*

when a system produces products, Q is ____________ than K

less -produces products while consuming reactants (thus increasing Q to match K).

A decrease in volume will cause the reaction to shift toward the side with

less moles of gas

A decrease in temperature will cause the reaction to shift toward the side with

lower enthalpy

An increase in volume will cause the reaction to shift toward the side with

more moles of gas

Heterogeneous equilibria involve reactants and products that are .....

not all in the same phases

When the reactant concentration decreases and the product concentration increases, the reaction will consume _____________ to make ______________

products, reactants

s. When writing equilibrium-constant expressions for heterogeneous reactions, generally the concentrations of _________ ____________ and ___________ are omitted

pure solids and liquids *b/c the composition of a pure solid or liquid does not change over the course of the reaction; only its quantity changes. Since its concentration isn't changing, the values can usually be excluded.*

A decrease in the value of Qc will increase the.....

reactants

When the reactant concentration increases and the product concentration decreases, the reaction will consume ____________to make ____________

reactants, products

For the reaction COCl2(g)⇌CO(g)+Cl2(g), K= 2.19×10^−10 at 373 K what can be said about this reaction at this temperature?

that the equilibrium lies far to the left *remember that K<10^-3, so anything above that would lie to the left *

What is the equilibrium constant, K, used to describe?

the concentration of reactants and products for a reaction in dynamic equilibrium.