Chapter 14 Concepts Flashcards
How do catalysts affect the equilibrium composition of a system?
They don’t, nor do they show up in the Kc expression
Which terms from the chemical equation are omitted?
Solids and liquids are omitted from the equation
`What terms go into Kc?
What does a large numerical value of Kc tell us?
A very large numerical value of Kc (or Kp) means that a reaction goes to “completion”
[products] >> [reactants] for K >> 1
What does a very small value of Kc tell us?
[products] << [reactants] for K << 1
What happens when Kc has an intermediate value?.
•When Kc has an intermediate value (» 0.01↔100), the both products and reactants have significant concentrations.
[products] = [reactants] for K=1 (not always exactly one
Adding chemical equations
Reversing a chemical reaction
Invert the Kc expression & take the inverse of Kc
Kc(new) = 1/Kc
Multiplying a chemical equation by a factor N
Raise Kc to the power N
Kc(new) = (KC)N
Balancing reminder
The balanced chemical equation must be written when citing a value for Kc. You must always make sure it is balanced after manipulating it
Your dumb roommate says that he/she knows a guy who had developed a palladium catalyst for the reaction above. It will only cost $1,000. Do you invest?
Though you are tired of saying it, you say yet again: “Are you nuts!!!!?” A catalyst does not change the equilibrium constant, only the reaction rate (both forward & backward). Having a faster way to get to a concentration of only 2.0×1017 M is not going to be worth your money. Go buy your roommate a chemistry textbook instead.
Effect of Changes in the Volume of the Container (equilibrium shift)
When the volume of a reaction vessel is decreased, the total pressure increases, so the partial pressures of all gases in the container increase. Following Le Chatelier’s principle, the reaction shifts to reduce the total pressure since that “undoes, in part” the disturbance. Thus the shift is in the direction which contains the fewest moles of gas.
Similarly, if the volume of the reaction vessel is increased, the total pressure decreases, and the shift is in the direction which contains the most moles gas.
In either case, if both sides of the equation have the same number of moles gas, the change in the volume of the container has no effect on the equilibrium.
What is the role of heat in an Exothermic reaction?
What is the role of heat in an Endothermic reaction?
How does removing or adding a solid affect a system?
Since concentrations of solids are constants and do not appear in expressions for Q or K, removing or adding some solid does not cause shifts. However, shifts in the equilibrium do change the amount of solid present!
