Brain Break
Reversible Reactions/Irreversible Reactions
Reaction Quotient
Equilibrium Constants
Le Chatelier's Principle
ICE
Modeling
Solubility
Pot Luck
100
I have keys but no locks. I have space but no room. You can enter, but you can’t go outside. What am I?
A keyboard
100
what is a reversible reason
a reaction that can happen in both directions simultaneously
100
What is a reaction quotient?
the reaction quotient (Q) is a measure of the concentrations of the reactants and products at a specific point in time.
100
What is an equilibrium constant?
The equilibrium constant, K, expresses the relationship between products and reactants of a reaction at equilibrium with respect to a specific unit.
100
What is Le Chatelier’s principle?
When a system at equilibrium is placed under stress, the system will undergo a change in such a way as to reduce the stress. If a system at equilibrium is disturbed by a change the system undergoes a temporary shift in order to restore equilibrium.
100
What side of the equilibrium is favored when Keq >1?
Products!
100
When you analyze a concentration vs time graph, how do to determine the time that equilibrium has been reached?
The lines are all parallel to one another.
100
The Ksp expression for KCl
Ksp = [K+][Cl-]
100
At what time on this graph can you use the data to 
Calculate K
20 seconds
200
What is the only letter that doesn’t appear in any U.S. state name?
Q
200
what is an irreversible reaction
a reaction in which the reactants convert to products and where the products cannot convert back to the reactants
200
How do you calculate Q?
Qc = [C]c[D]d / [A]a[B]b (using concentrations)
200
How do you calculate K?
K = [C]c[D]d / [A]a[B]b
200
What change can stress Equilibrium (Keq)?
Temperature
200
Consider the following reaction:
2 XY(g) ⇄ X2(g) + Y2(g)
This equilibrium has a value of Keq = ???. If 7.0 moles of XY are injected into a 2.5 L container at 25°C , and reaches equilibrium with a concentration of 2M, find the equilibrium Keq.
Keq = 0.04
200
When analyzing a particulate model for the following equilibrium: A + B <=> AB, the model shows 10 A, 10 B and 5 AB at equilibrium. Does this model favor the products or reactants?
reactants! there are more reactants than products at EQ.
200
What is Ksp?
The solubility constant; the degree to which a compound is soluble in water.
200
Given the graph below and the equation A+B->2C calculate the value of Kc numerically (3 sig figs).
2.67
300
What is the largest planet in our solar system?
Jupiter
300
N2 + 3 H2 ⇌ 2 NH3
ΔH = -92kJ/mol
Which direction would equilibrium shift to when heat is added?
Left (Higher energy side)
300
how do you find if it shifts left or right?
Check whether Q or K is greater or less than (put k always on left side and the greater than or less than side will point to the direction of the shifts)
300
If the equilibrium constant has a lot of reactants where does the equilibrium lie?
Equilibrium lies to the left
300
If you add products to the system which way, does it shift?
The equilibrium will shift to the left, favoring the formation of more reactants to consume the added products.
300
There are 8 moles of A and 10 moles of B in a 2.0 L solution. At equilibrium [D] = 2 M. Solve for Keq. Are products or reactants favored?
2A (g) + 3B (aq) ⇄ C(l) + 2D (g)
Keq = 0.125
Reactants Favored
300
Draw a particulate that models a Keq > 1
Reaction: A + B <-> AB
More AB particles than A and B particles.
300
There are two solids, solid A has a Ksp of 0.2. Solid B has a Ksp of 1.1x10-5. Which dissociates better in water?
Solid A
300
Given that Kc=[FeSCN2+]/([Fe3+][SCN-]), explain the stress and the response in terms of BOTH products and reactants
There is a sharp decline in the reactant Fe3+ so products is consumed and decreases. Reactants are formed and increase.
400
A cowboy rode into town on Friday. He stayed three days and left on Friday. How is that possible?
His horse’s name is Friday
400
What will happen to the position of equilibrium of this reaction was put under less pressure?
Br2 (g) + Cl2 (g) ⇌ 2 BrCl(g)
∆H = +14 kJ/mol
No change (equal number of moles)
400
2CH4(g) <-> C2H2 (g) + 3H2 (g) Kc= 0.154 at 2000K Starts of with 4.00 M CH4, 2.00 M C2H2, and 3.00 M H2 which direction will the reactin progress to reach equilibrium?
Q>K, so a net reaction occurs to the left.
Q=[C2H2][H2]3/[CH4]2
Q=3.38
3.38>.154
Q>K
400
Consider the following reversible reaction. In a 3.00 liter container, the following amounts are found in equilibrium at 400 oC: 0.0420 mole N2, 0.516 mole H2 and 0.0357 mole NH3. Evaluate Kc.
N2(g) + 3H2(g) ⇌ 2NH3(g)
Kc=1.99
400
The following reaction is to reach equilibrium.
CaO(s) + CO2(g) ⇌ CaCO3(s)
What happens to the reaction when some CaCO3 (s) is removed?
Nothing: The reaction is still at equilibrium (CaCO3 is a solid)
400
In a container of 1.0 L volume, I mix 1.0 mol N2, 1.0 mol H2 and 0.5 mol O2. Write an ICE table when the equilibrium concentration of N2H4 is 0.1M. Are reactants or products favored?
N2(g) + 4 H2(g) + O2(g) <--> N2H4(g) + 2 H2O(g)
Keq = 0.087 (REACTANTS)
400
In a Concentration vs. Time graph, when the lines intersect, what does that signify? When do you know if equilibrium has been established?
1) Intersection = equal concentration
2) Equilibrium = No longer changing concentration
400
The value of Ksp of AgCl is 1.8 x 10-10. What would be the concentration of Ag+ and Cl- in a saturated solution of AgCl?
0.000013 M or 1.3 x 10-5 M
400
20 minutes
500
What has hands but can’t clap?
A clock
500
N2 + 3 H2 ⇌ 2 NH3 ΔH = - 92kJ/mol
Which direction would equilibrium shift when a catalyst is successfully added.
No change/shift.
** Catalysts speed reactions, but don't make more of anything.
500
If Kc = 0.0142 and the initial concentrations are 1.0 M NOBr, 0.2M NO, and 0.8M Br₂, which way will the reaction progress to reach equilibrium?
Q = 0.032 and Q > 0.0142 ⇒ Q > K ⇒ the reaction will proceed to the left because we have passed K.
500
Nitrosyl chloride, NOCl, dissociates on heating as shown below. When a 1.50 gram sample of pure NOCl is heated at 350oC in a volume of 1.00 liter, the percent dissociation is found to be 57.2%. Calculate Kc for the reaction as written.
NOCl(g) ⇌ NO(g) + 1/2 Cl2(g)
Kc= 0.107
500
What would be the effect of reducing the volume of a container in which the following system was at equilibrium?
2NO(g) + O2(g) ⇌ 2NO2(g)
increase [NO2]
500
H2(g)+I2(g)⇌2HI(g)
At a certain temperature, the equilibrium constant Keq is 49.0. Initially, a container holds 1.00 M H₂ and 1.00 M I₂. What are the concentrations at equilibrium?
[H2]=[I2]=1.00−x=0.222M
[HI] = 2x = 1.556
500
3 H2 (g) + N2 (g) <--> 2 NH3 (g)
Initially, you place 8 moles of H2 and 6 moles of N2 in a 2.0 L container. At equilibrium, the concentration of NH3 is 2 M. Find all the equilibrium concentration of all chemicals and then produce a particulate model showing what is in the container at equilibrium.
2 moles of H2
4 moles of N2
4 mole of NH3
500
The molar solubility of Ag2S is 1.3x10-4. What is it's Ksp?
8.8x10-12
Ksp=(2s)2⋅(s)=4s3
Ksp=4⋅(1.3×10−4)3
500
H2(g)+F2(g)=2HF
ΔH= −542kJ
When the lab warms up the reaction will shift to the ________
Left