K Values & Magnitude
What does it mean if the equilibrium constant K is much greater than 1?
The reaction favors products at equilibrium.
In an ICE table, what does the “C” row represent?
The change in concentration of each substance as the system moves toward equilibrium.
What does the symbol Q represent in equilibrium?
The reaction quotient—a value calculated the same way as K, but using concentrations at any point, not just at equilibrium.
What does it mean when a reaction has reached equilibrium?
The rate of the forward reaction equals the rate of the reverse reaction, and concentrations remain constant.
Which fictional character lives in a pineapple under the sea?
SpongeBob SquarePants
If a reaction has a K = 1.0 × 10⁻⁷, what does this tell you about the amounts of reactants and products?
There are mostly reactants at equilibrium, with very little product formed.
Fill in the missing value in this ICE table setup for the reaction: H₂ + I₂ ⇌ 2 HI, initial [HI] = 0.0 M, at equilibrium [HI] = 1.0 M.
What is the change in [HI]?
+1.0 M
If Q < K, which direction will the reaction shift?
The reaction will shift right, toward the products, to reach equilibrium.
True or False: At equilibrium, the concentrations of reactants and products are always equal.
False – they are constant, but not necessarily equal.
What’s the top-selling ice cream flavor in the U.S.?
Vanilla (classic never goes out of style 🍦)
For the reaction A ⇌ B, if K ≈ 1, what can you say about the concentrations of A and B at equilibrium?
There are comparable amounts of both reactants and products.
You begin with [H₂] = 1.0 M and [Cl₂] = 1.0 M. No HCl is present initially. At equilibrium, [HCl] = 1.8 M.
What is the change in [H₂]?
–0.90 M
(Because HCl forms with a 2:1 ratio, so 2x = 1.8 → x = 0.90 M, and H₂ decreases by x)
If Q = K, what is happening in the reaction system?
The system is already at equilibrium, so there is no net shift in either direction.
What type of system is required for a chemical reaction to reach equilibrium?
A closed system, so that no reactants or products can escape.
Which Disney song could describe a reaction at equilibrium?
“Let It Go” — because everything is balanced and not changing anymore!
A student finds K = 2.5 × 10³ for a reaction. What type of chemical system does this describe, and how should the equilibrium arrow be drawn?
A product-favored system; the equilibrium arrow should point mostly to the right (→).
For the reaction N₂ + 3H₂ ⇌ 2NH₃, you start with [N₂] = 0.500 M and [H₂] = 1.500 M. At equilibrium, [NH₃] = 0.400 M.
What are the equilibrium concentrations of N₂ and H₂?
[N₂] = 0.500 – 0.200 = 0.300 M
[H₂] = 1.500 – 3×0.200 = 0.900 M
(Because 2x = 0.400, so x = 0.200)
For the reaction A ⇌ B, K = 10. At a certain point: [A] = 2.0 M and [B] = 1.0 M.
Calculate Q and predict the direction of the shift.
Q=[A][B]=2.01.0=0.5⇒Q<K⇒Shifts right
Identify one example of a physical system that reaches equilibrium.
Examples include:
A sealed bottle of soda (CO₂ gas ⇌ dissolved CO₂)
Water in a sealed container at a constant temperature (evaporation ⇌ condensation)
What is my favorite item from the vending machine?
Hot Cheetos, Apple Juice, and Honeybun
Reaction A has K = 1.2 × 10⁻⁴, and reaction B has K = 8.5 × 10². Which reaction favors products more and why?
: Reaction B favors products more because it has a much larger K value, indicating a higher product concentration at equilibrium.
For the reaction A ⇌ B + C, you start with [A] = 0.800 M, [B] = 0 M, and [C] = 0 M.
At equilibrium, [B] = 0.600 M. Calculate the value of the equilibrium constant K.
[A] = 0.800 – 0.600 = 0.200 M
[B] = [C] = 0.600 M
K=[B][C][A]=(0.600)(0.600)0.200=0.360.20=1.8K = \frac{[B][C]}{[A]} = \frac{(0.600)(0.600)}{0.200} = \frac{0.36}{0.20} = \boxed{1.8}K=[A][B][C]=0.200(0.600)(0.600)=0.200.36=1.8
Consider the reaction 2 NO₂ ⇌ N₂O₄, where K = 0.25.
If [NO₂] = 0.60 M and [N₂O₄] = 0.20 M, calculate Q and determine the shift.
Q=[NO2]2[N2O4]=(0.60)20.20=0.360.20≈0.56⇒Q>K⇒Shifts left
In a reaction where equilibrium is established quickly, what does that tell us about the rates of the forward and reverse reactions?
Both reactions occur rapidly, and they quickly reach a point where their rates are equal, even though the actual amounts of products/reactants may vary.
Finish the joke: Why did the chemist break up with the equilibrium reaction?
Because it was too one-sided... until it finally balanced out.