equilibrium and thermodynamics Flashcards
reaction reversibility
products are converted to reactants at the same time reactants are converted to products
rate of chemical reaction depends on what
amount of reactant present
dynamic equilibrium
where the forward reaction occurs at the same rate as the reverse reaction and there is no change in reactant/product concentration
equilibrium constant K eq
[p]/[r]
what does a keq> 1 mean
products> reactants so the product is favored
- will go in forward direction
what does a keq<1 mean
reactants are favored and reaction will go in the reverse reaction
when calculating keq, what is ommited?
pure liquids (h2O) and pure solids
keq of forward related to reverse
inverse –> 1/Keq
can keq be negative
no, concentrations of p and r are not negative
what is equillibrium constant dependent on
concentrations of product/reactant and temperature
rection quotient
same as the equation for equilibrium constant but the concentrations can be used from any time, not just at equilibrium
- still should not include pure liquids and solids
purpose of reaction quotient
predicts which direction an equation will move in order to establish equillibrium
when Q < Keq
the ratio of products to reactants is lower than at equillibrium so the equation is pushed in the forward direction
when Q > Keq
the ratio of products to reactants is higher than it would be at equilibrium so it is pushed in the reverse reaction
when Q = Keq
reaction has reached dynamic equilibrium
le chatlier’s principle
when equilibrium is disrputed, the reaction will move in the direction that favors the restoration of equ.
if excess reactant is added how does the system correct equillibrium?
form more product
- reaction shifts forward
if reactant is removed how does the system correct equillibruim
favors the reverse reaction to make more reactant
if product is added how does the system correct equilibrium
favors reverse reaction
if product is removed how does the system correct equilibrium
favors forward reaction
what happens to a system if the volume is increased
pressure is decreased
- shifts toward the side with more moles of gas
what happens to a system if the pressure is increased
volume decrease
- shift toward side with less moles of gas
what happens to reestablish equilibrium when temperature is added
if ΔH> 0 shift toward products if ΔH< 0 shift toward reactants
what happens to reestablish equilibrium if temperature is reduced
if ΔH> 0 shift toward reactants if ΔH< 0 shift toward products
what happens to equilbrium if a catalyst is added after the reaction reaches dynamic equilibrium
nothing because catalyst only increases rate of reaction and does not change concentrations of p and r
temperature
average kinetic energy
kelvin to celcius conversion
K = c +273
absolute 0
when temperature is 0K or -273 celcius and has perfect crystal structure/no entropy
- all motion stops
if two systems are in thermal equilibrium with one another, what kind of heat transfer occurs?
no heat transfer would occur because temperature of each system is the same
open system
can exchange heat and matter with sorroundings
closed system
energy can be transfered but not matter
isolated systems
cant transfer heat or matter with surroundings
first law of thermodynamics
applies to closed systems
ΔU = Q -ΔW
work done by the system
positive
work done by the surroundings on the system
negative
calorimetry
measure heat exchange
caorimetry equation
Q=mcΔT
q - heat
m - mass
c - constant
t - temp
enthalpy
measurement of heat (J)
describes changes to a system
gain or loss of thermal energy
enthalpy equation
ΔH= ΔU +PΔV
u - internal energy
internal enthalpy equation
ΔH= ΔU -pΔV
q
enthalpy
heat gained or lost from the system
endothermic
+ΔH
requires heat input
exothermic
-ΔH
releases heat
standard enthalpy
1 atm and 25C
standard enthalpy of formation
change in enthalpy associated with formation of one mole of compound under standard conditions
- always zero for compounds in standard state
standard heat of formation
same thing as standard enthalpy of. formation
stanard enthalpy of reaction
enthalpy of products - reactants
is standard enthalpy a state or path function
state function , does not care about the path, only concerned with the difference in products and reactants
bond dissociation energy
enthalpy change associated with breaking bonds
ΔHrxn = ΔH (bonds broken)- ΔH (bonds formed)
is the formation of bonds exothermic or endothermic
exothermic
is bond breakage exothermic or endothermic
endothermic
+ΔH
endothermic
Hess’s law
enthalpy changes in individual steps can be added up to find the total change in enthalpy
entropy
the freedom a molecule has to exsist in multiple states
- value of disorder
what molecules have low entropy
solids
what molecules have high entropy
gases
second law of thermodynamics
in an isolated system, entropy inevitably increases
- in a heat transfer the molecules will move randomly and favorably from high temp to low temp
what is true of entropy in a completely isolated system
entropy will NEVER decrease, only increase
Δs+
positive/ favorable reactions
-Δs
decreases in entropy
- nonfavorable
standard entropy
change in entropy at standard conditions
Δsrxn = ΔSp- ΔSr
gibbs free energy
maximum amount of work performed by a system
- tells spontaneity of rxn
- affected by temp, enthalpy, entropy
gibbs free energy eqn
ΔG = ΔH- TΔS
reaction coordinate diagrams
energy changes associated with a reaction as it is converted from reactants to products
transition state
highly unstable, highest energy portion of a reaction
aka energy of activation
energy of activation
highly unstable and instantaneous barrier to a reaction that must be overcome to complete a reaction
ΔG of reaction
energy of products - energy of reactants
- determines spontaneity of reaction
ΔG+
nonspontaneous reaction
endergonic
ΔG-
spontaneous reaction
exergonic
spontaneous
reaction that can proceed without additional force
- not affected by enzymes
if ΔH is positive and ΔS is negative when is the reactoin spontaneous
never
if both ΔH and ΔsS are negative when is ΔG spontaneous
only at low temps
if ΔH is - and ΔS is positive when is ΔG spontateous
always
gibbs free energy of formation
ΔGp - ΔGr
gibbs free energy equillibrium eqn
ΔG = -RTLnKeq
thermodynamic product
more stable product
ΔG more negative
slower and higher energy of activation
can be steric hinderance
not favored at low temp
kinetic product
faster formation with lower activation energy
- less stable
- low temp
which product forms more quickly
kinetic
which product forms more slowly
thermodynamic
which product is less stable thermodynamically
kinetic
which product requires a lower energy of activation
kinetic
whihc product is favored at low temperatures
kinetic
which product is favored at high temperatures
thermodynamic
