Chapter 14 Flashcards
EQUATION Equilibrium constant
[Products]^coefficients / [Reactants]^coefficients
K_c is affected by a change in _____ but not in ______.
temperature, initial concentration
A K_c value close to 1 means that the reaction
pretty much favors neither direction.
A very _____ K_c value means the reaction essentially goes to completion, while a very ______ K_c value means that the forward reaction barely occurs at all.
large, small
Restate the rate law just so it’s not confusing with the K_c equation. What is the usefulness of the rate law?
rate = k[reactants]^orders. The rate law relates rate to concentration. K_c, in contrast, is a constant and can tell us which direction a reaction will proceed.
If you invert an equation with K_c equilibrium constant, what will the new equation’s equilibrium constant look like?
1 / K_c
If you double an equation with K_c equilibrium constant, what will the new equation’s equilibrium constant look like?
(K_c)^2. Remember that coefficients in the equation are applied as exponents in the K_c equation.
T/F: The only thing you never want to include in a K_c equation is a pure solid (indicated by (s)).
F. You also never want to include a pure liquid, (l).
T/F: The K_c for an overall reaction is equal to the product of the K_c of contributing reactions.
T
T/F: If an equation contains some gases, it’s possible to write an equilibrium constant expression in terms of partial pressures, or K_p.
F. It has to contain only gases!
How does K_p relate to K_c?
K_p = K_c(RT)^Δn gas.
What is Δn gas?
The change in number of moles of gas as the reaction occurs in the forward direction. So, Δn gas = (moles gaseous products – moles gaseous reactants)
EQUATION Reaction quotient
Q_c = ([products]^stoichiometric coefficients) / ([reactants]^stoichiometric coefficients)
T/F: Q_c only works for non-equilibrium conditions.
T. Non-equilibrium conditions only! It’s in contrast to equilibrium constants like K_c or K_p.
If K_c represents what will happen to a reaction, Q_c describes what _________ to a reaction.
is happening
If Q_c is ______ than K_c, the reaction will proceed to the right (products will form); but if Q_c is ______ than K_c, the reaction will proceed to the left (reactants will form).
smaller, greater
Think about what this means. A large Q_c value must have large values for [products]. If it has so many products, it has “overstepped its boundaries” and the reaction will start making reactants instead.
Le Châtelier’s principle states that a reaction equilibrium will push back if you make changes to any of what four things?
1) Temperature
2) Concentration
3) Pressure
4) Volume
There is another list of four things that affect the rate of reaction, and it’s not the same list! What’s on this one?
1) Temperature
2) Concentration
3) Surface area
4) Catalysts
Increasing the concentration of reactants or decreasing the concentration of products will make the reaction shift back to the ___. How does this affect Q_c values?
right (more products)
This will make Q_c smaller.
Decreasing the concentration of reactants or increasing the concentration of products will make the reaction shift back to the ___. How does this affect Q_c values?
left (more reactants)
This will make Q_c larger.
T/F: Just like for K_c equations, you never want to include pure solids or liquids in your Q_c equations.
T
Increasing pressure will favor the side of a chemical equation with ______, and decreasing pressure will favor the side of a chemical equation with ______.
the fewest moles of molecules, the most moles of molecules
T/F: Because pressure changes will favor one side of an equation based on the amount of moles it has, pressure changes always have an effect on a chemical equation’s state of equilibrium.
F. Not if both sides of the equation have an equal amount of moles of molecules!
Because heat is written on the _____ side of an exothermic equation, adding heat to an exothermic equation will favor the ____ side of that equation.
right (products), left (reactants)
