Week Eight Flashcards
Entropy
spontaneous processes tend to proceed from states of low probability to states of higher probabilty
spontaneous processes tend to disperse energy
Delta S
Sproducts - Sreactants
Spontaneous event
accompanied by an increase in entropy of the system
Entropy change of a process
change in heat/ temp
Factors that affect entropy
volume
temperature
physical state
number of particles
Volume
possible to predict whether delta S is positive or negative
entropy increases with increasing volume for gases
Temperature
higher the temp, higher the entropy
Physical state
solid –> liquid –> gas
Number of particles
when all other things are equal, reactions that increase the number of particles in the system tend to have positive entropy change
Second law of thermodynamics
whenever spontaneous event occurs in universe, total entropy of the universe increases
Entropy change of universe equation
= entropy change of system + entropy change of surroundings
Entropy change for surroundings
equal to heat transferred to surroundings from system / Temp
Change in entropy surroundings
change in heat surroundings/ temperature
Change of entropy system
- change in heat surroundings/ temperature or - change enthalpy system/ temperature
Total entropy change
change of entropy system - change in enthalpy system/ temperature
Gibbs free energy
H - T x s
Gibbs free energy change
delta H - T x delta S
Third Law of thermodynamics
at absolute zero, the entropy of a perfectly ordered pure crystalline substance is zero
provides point at which absolute entropy is known
Standard entropy
entropy of 1 mol of a substance determined at standard conditions at a temp of 298K
Entropy positive - enthalpy positive
spontaneous at high temps, non spontaneous at low temps
Entropy positive - enthalpy negative
spontaneous at all temps
Entropy negative - enthalpy positive
non spontaneous at all temps
Entropy negative - enthalpy negative
non spontaneous at high temps, spontaneous at low temps
Standard gibbs free energy change
when change in gibbs is determined at standard pressure, this is called standard free energy change
Standard free energy change
change in Heat at standard - temp x change in entropy at standard
Maximum conversion of chemical energy into work
can only occur if a process is thermodynamically reversible Requires the system to operate at equilibrium constantly
Equilibrium
when a reactions forward and reverse reactions are occuring at same speed
no net change in overall composition
Kc
equilbrium constant
Kc equation
{A}^a {B}^btemperature effect on Kc
dependent on temp so temp is always specified
Qc
reaction quotient
same as equilbirum equation but not all values are at equilbrium
Kc rules
can only have one positive value at specific temp
QC rules
can have multiple positive values
Qc = Kc
at equilibrium
Qc> Kc
when system reacts to use up all products and generate more reactants
Qc< Kc
when system reacts to use up all reactants and generates more products
Kp
uses partial pressure to specify the quantity of the two gases
Kp equation
Kp = kc x (RxT / standard pressure)^ delta n gas
number of moles
n/1 mol
Delta n gas
(number of moles of gaseous products) - number of moles of gaseous reactants)
Kc’
1/ Kc
when reaction is flipped
Kc< 1
more reactant
Kc = 1
same amounts of products and reactants
Kc > 1
more product
Homogeneous
all reactants and products are in same phase
Heterogeneous
more than one phase
Kc - structure of molecules
cant include the concentration of pure solids or pure liquids
Pure liquids and solids at constant temp
ratio of amount of substance to volume of substance is constant
