Thermodynamics Flashcards
Thermodynamics
the study of energy and its transformations
Energy
the capacity to do work or transfer heat
work
the movement of an object abasing some force; force is a push or pull exerted on an object
heat
flow of energy from a body at higher temp. to one at a lower temp when they are placed in thermal contact
kinetic energy
the energy an object has due to its motion
potential energy
stored energy that results from the position
system
part of the universe we single out
surroundings
everything that exist outside the system
open system
can exchange both energy and matter with surroundings. ex chem Rxn in open flask
closed system
a system can exchange energy but not matter with surroundings. ex. chem rxn in stoppered flask
isolated system
can exchange neither matter nor energy with its surroundings. ex. sealed flask that is thermally, electrically, mechanically insulated
internal energy (U)
the sum of all kinetic and potential energy contribution
ΔU= w + q
equation for finding internal energy of a system. w=work q=heat
If w done onto system
w is greater than 0
If w done by system
w is smaller than 0
if q is absorbed from the surroundings, q>0 and the process is
endothermic
if q is released to the surroundings, q<0 then the process is
exothermic
When heat is added to a system or work is done on a system
its internal energy (U) increases
First law of thermodynamics
Energy can be transferred and transformed, but it cannot be created or destroyed.
Internal energy of an isolated system is
constant
3 examples of forms of energy
work, heat and light
Enthalpy (H)
related to the internal energy of a system plus the product of the pressure and volume of system
H= U + PV
Constant pressure w
-P∆V
when the reaction is not kept at a constant volume this equation is used for enthalpy
ΔH=ΔU + PΔV
When change in ΔH is positive, the process is
endothermic, it gained heat from the surroundings
ΔH<0 the process is
exothermic, it released heat to the surroundings
the process by which a drug particle dissolves is called
dissolution
breaking solute-solute attractions is
endothermic
breaking solvent-solvent attractions is
endothermic
forming solute-solvent attractions is
exothermic
Enthalpy change
sum of endothermic and exothermic interactions
spontaneous processes
- occur without outside assistance
- occurs in a definite direction
- they are spontaneous in one direction and non spontaneous in the reverse
NaOH dissolving in water
- Heat is liberated (exothermic)
- ∆H is negative
NaNO3 dissolving in water
- Solution becomes cooler
- Heat is absorbed ( endothermic)
- ∆H is positive
reversible process
a system can be completely restored to its original condition with no net change to system or surroundings
irreversible process
can’t be reversed to restore the system and surroundings to original state. all real processes that occur on their own are irreversible
spontaneous processes are
irreversible: even if the system is restored to the original condition, the surroundings will have changed
Entropy
measurement of randomness or disorder
- when a system becomes more chaotic, its entropy increases
Second law of thermodynamics
any irreversible process results in an increase in entropy
Primary reason for Micelle formation
- attainment of a state of minimum free energy
- ex of thermodynamics
Surface tension
- force per unit length that must be applied parallel to the surface as to counterbalance the net inward pull
Contraction
is spontaneous and the contracted surface represents a minimum free energy state
Surfactants are
- amphiphilic molecules ( have hydrophobic and hydrophilic parts)
- orient themselves at the surface to remove the hydrophobic group from the aqueous environment
Micelles form when
the surface layer is saturated with surfactant molecules and no further decrease in surface tension is possible
which is most important in determining the free energy change
entropy
- in solution, hydrophobic molecules are surrounded by structured water
What results in an increase in entropy
- loss of ordered structure of the water molecules when the hydrophobic regions of the surfactant are removed
Third Law of Thermodynamics
- entropy of a perfectly organized crystal at absolute zero is zero
In any dissolution, the entropy of a system
increases
Gibbs free energy equation
ΔG = ΔH - TΔS
Total entropy change
∆Stotal= ∆S+∆Ssurroundings
For a spontaneous change, S is
positive, >0
At constant Temperature and pressure, if ΔG>0 (positive) the reaction is
non spontaneous in the forward direction but spontaneous in the reverse rxn
At constant Temperature and pressure, if ΔG<0 (negative) the reaction is
spontaneous in the forward reaction
At constant Temperature and pressure, if ΔG=0 the reaction is
at equilibrium
Equilibrium expression. K=
[C]^c[D]^d / [A]^a[B]^b
If K and lnK <0 (negative), then ∆G is
positive
If K and lnK >0 (positive), then ∆G is
negative
If K and lnK =0, then ∆G is
=0
The more negative ∆G,
the larger the equilibrium constant
Oth Law
If two systems are at the same time in thermal equilibrium with a third, then all three are in thermal equilibrium
