unit 9 Flashcards
reversible reaction
a reaction that can proceed in both the forward and reverse directions
dynamic equilibrium
the rate of the reverse reaction equals the rate of the forward reaction
(this does not mean that [reactants] and [products] are equal to one another at equilibrium)
Equilibrium constant (K)
Quantifies the relationship between [reactants] and [products] at equilibrium
K = [products]/[reactants]
significance of large K
(K»_space; 1)
forward reaction is favored
-K lies far to right
-high [product] and low [reactant] at equilibrium
-forward reaction proceeds essentially to completion
significance of small K
(K «_space;1)
-reverse reaction is favored
-K lies far to left
-Low [product] and high [reactant] at equilibrium
-Forward reaction does not proceed very far
if you reverse the equation, _ K
invert
what happens to K when you multiply the coefficients in the equation?
raise K by the same factor you multiplied the coefficients
what do you do to K when you add two or more individual chemical equations to each other to obtain an overall equation?
multiply K’s from all equations
What is dynamic equilibrium? Why is it called dynamic?
Rate of the forward reaction = rate of the reverse reaction
Even though [reactants] and [products] remain constant, both the forward and reverse reactions are occurring-reactants and products form at the same rate that they are depleted
What is the significance of the equilibrium constant? What does a large equilibrium constant tell us about a reaction? A small one?
Indicates if the forward reaction (large K) or the reverse reaction (small K) is favored
concentration of gas equation
n/V = P/RT
pressure of a gas and concentration proportion
direct
Kc
equilibrium constant expressed in terms of concentrations of reactants and products
Kp
equilibrium constant for gaseous reactions, expressed in terms of partial pressure in atm
is the partial pressure of a gas in atm the same as the molar concentration of that gas?
no
Kc and Kp are only equal when
there is no change in the number of gas phase particles during the reaction
gas particle change equation
Kp = Kc (RT)^∆n
∆n = mol products - mol reactants
Explain the difference between Kc and Kp. For a given reaction, how are the two constants related?
Kc is the equilibrium constant with respect to concentration in molarity
Kp is the equilibrium constant for gaseous reactions in terms of partial pressures
why don’t pure liquids/solids included in equilibrium expressions?
their concentrations do not change in the course of the reaction
they’re incorporated into values of Kc or Kp
ONLY INCLUDE GASES IN EQUILIBRIUM EXPRESSION
The equilibrium [reactants] and [products] can vary depending on
their initial concentrations
the equilibrium constant is always constant at
any temp, regardless of initial concentrations
reaction quotient (Qc)
gauges the progress of a reaction relative to equilibrium, when the reaction mixture is not at equilibrium and contains reactants and products
-same as equilibrium constant, doesn’t need to be at equillibrium
differences between Kc and Qc:
-Kc has only one value and specifies relative amounts of reactants and products at equilibrium
-Qc depends on the current state of the reaction and has many different values as the reaction proceeds
what is the value of Qc when there are only reactants?
0
what is the value of Qc when there are only products?
infinity
what is the value of Qc when there are equal amounts of products and reactants?
1
what happens when Q < K?
Reaction goes to the right (towards products)
what happens when Q > K?
Reaction goes to the left (towards reactants)
what happens when Q = K?
equilibrium
when the equilibrium constant is small, will the reaction proceed far?
no
Le Chatelier’s Principle
When a chemical system at equilibrium is disturbed, the system shifts in a direction that minimizes the disturbance.
A chemical system can be disturbed by changing [reactant] or [product], changing volume or pressure and changing temperature.
volume and pressure proportion
inversely related
if a system is at equilibrium, what happens when you decrease the volume?
the reaction shifts in the direction that has fewer moles of gas particles
if a system is at equilibrium, what happens when you increase the volume?
the reaction shifts in the direction that has greater moles of gas particles
does adding an inert gas to the mixture have an effect on the equilibrium?
no
Increasing the concentration of one or more reactants (makes Q < K) causes the reaction to shift to the
right (toward products)
Increasing the concentration of one or more products (makes Q > K) causes the reaction to shift to the
left (toward reactants)
Decreasing the concentration of one or more reactants (makes Q > K) causes the reaction to shift to the
left (toward reactants)
Decreasing the concentration of one or more products (makes Q < K) causes the reaction to shift to the
right (toward products)
is a reaction has the same number of gas particles on both sides, what happens when the volume changes?
nothing
what happens when you increase the temp in an exothermic reaction?
reaction shifts left
K decreases
what happens when you decrease the temp in an exothermic reaction?
reaction shifts right
K increases
what happens when you increase the temp in an endothermic reaction?
reaction shifts right
K increases
what happens when you decrease the temp in an endothermic reaction?
reaction shifts left
K decreases
do catalysts affect the position of equilibrium?
no
solubility product constant (Ksp)
equilibrium constant for dissolution of an ionic compound
(measure of solubility)
molar solubility
solubility in units of mol/L
-only one value at a given temp
-can have different values in different types of solutions
what is lower, the solubility of an ionic compound in a solution containing a common ion or the solubility of an ionic compound in water?
in solution containing a common ion
what happens when you add a soluble salt to a reaction that contains an insoluble salt?
it increases the solubility of the insoluble salt
