Chapter 15 Flashcards
When a reaction is in equilibrium…
- The rate at which products are formed from reactants equals the rate at which reactants are formed from products.
- Concentrations cease to change
- The reaction appears to stop before completion has been reached
Chemical Equilibrium
Takes place when the forward and reverse reactions proceed at EQUAL RATES
Dynamic Equilibrium
A state of equilibrium in which the forward and reverse processes take place at equal rates so that NO NET CHANGE OCCURS
Static Equilibrium
A state of equilibrium in which the object DOES NOT MOVE (like the rope in tug of war)
Equilibrium State
A mixture of reactants and products whose concentrations no longer change with time
Equilibrium is expressed in a reaction by:
2 arrows pointing opposite directions (left and right)
Both the forward and reverse reactions in an equilibrium reaction…
Are elementary
The rate constant for a forward reaction is expressed by:
Kf
The rate constant for a reverse reaction is expressed by:
Kr
Kf / Kr gives you…
a constant
*****True or False: When a reaction reaches equilibrium, Kf and Kr are equal
FALSE!
*****True or False: When a reaction reaches equilibrium, The forward and reverse reaction RATES are equal
TRUE!
*****True or False: When a reaction reaches equilibrium, the concentrations of the reactants and products are equal
FALSE! They no longer change once equilibrium is reached, but this does NOT mean that their concentrations are equal
Why does the rate of the forward reaction slow down as the reaction proceeds?
Because the concentration of reactants is decreasing, which reduces frequency of collisions, and hence the rate of the forward reaction decreases.
At equilibrium, the concentrations of reactants and products…
No longer change
*****True or False: For equilibrium to occur, neither reactants nor products can escape from the system
TRUE!
At equilibrium, a particular ratio of concentration terms equal…
a constant
True or False: Whether the reaction starts out with only products or only reactants, the equilibrium condition can be reached
TRUE!
True or False: You cannot determine if equilibrium has been reached by monitoring the concentration of a single reactant
FALSE! You CAN tell based on a single reactant
What is the equilibrium constant represented by?
Kc
The equilibrium constant expression (Kc = [D]^d[C]^c/ [A]^a[B]^b) depends ONLY on:
The stoichiometry of the reaction
The value of Kc depends on…
TEMP, NOT INITIAL CONCENTRATIONS OF REACTANTS AND PRODUCTS
What are the units for Kc?
Kc DOES NOT HAVE UNITS
True or false: The value of Kc depends on starting concentrations
FALSE
For GASES, the equilibrium constant and equilibrium-constant-expression can be written in terms of
Partial Pressures!
The units used for partial pressure are…
ATM!!!!
Do Kp and Kc generally have the same numerical values?
NO! But conversions can be made between the two
*****When does Kp equal Kc???
When the number of moles of gaseous products and number of moles of gaseous reactants are equal
What are “activities”?
Equilibrium constants derived from thermodynamic measurements
If a reaction is exothermic and produces large quantities of heat reaching equilibrium, its equilibrium constant must be…
GREATER THAN ZERO
If K»1…
Large K
Equilibrium lies to the RIGHT
PRODUCTS PREDOMINATE
If K«1…
Small K
Equilibrium lies fo the LEFT
REACTANTS PREDOMINATE
The equilibrium constant of a reaction in the reverse direction is…
the INVERSE (or reciprocal) of the equilibrium constant in the forward direction
The equilibrium constant of a reaction that is multiplies by n is in fact…
raised to the POWER OF n
The equilibrium constant for a net reaction made up by adding two or more reactions is…
the PRODUCT of the equilibrium constants for the individual reactions
Homogeneous Equilibria is defined as
Equilibrium that takes place between substances that are ALL IN THE SAME PHASE (solid, liquid, gas)
Heterogeneous Equilibria is defined as
Equilibrium that takes place between substances that are in different phases
True or False: the concentrations of pure solids and pure liquids are expressed in the equilibrium-constant-expression
FALSE! Whenever a pure solid or pure liquid is involved in a HETEROGENEOUS equilibrium, its concentration is NOT included in the equilibrium-constant-expression
If a reaction is exothermic and produces large quantities of heat reaching equilibrium, its Kc will be…
Greater than zero!
