LAWS & DEFINITIONS Flashcards
(13 cards)
First Law of Thermodynamics
Energy cannot be created or destroyed, only transformed from one form to another.
∆U = q + w
change in internal energy is equal to some amount of heat and work done on the system.
Second Law of Thermodynamics
in a spontaneous reaction, the entropy of the UNIVERSE must increase. ∆S(univ) > 0
At equilibrium, ∆S(univ) = ∆S(sys)+∆S(surr) = 0
Third Law of Thermodynamics
the entropy of a closed system at thermodynamic equilibrium approaches a constant value as the temperature approaches absolute zero.
for a perfect crystal, entropy = 0 at T = 0K.
Define heat.
the transfer of energy from a hotter body to a cooler one (ie. transfer of energy as a result of T difference)
Define work.
work is done when moving against a force.
Define internal energy.
A property that an object possesses
“stored” inside a substance as the kinetic energy of the particles and the energy of interaction between particles.
closely related to temperature.
main difference between internal energy and heat/work
internal energy is a STATE function, heat and work are PATH functions
Define entropy (classical definition)
dS = ∂q(rev) / T
for the entropy of the object that has absorbed some amount of heat
Define reversible process
an EQUILIRBIUM process
a process whose direction can be changed by an infinitesimal change in some variable
Infinitely slow
do maximum work
Define spontaneous process
inherently IRREVERSIBLE
NOT at equilibrium
ENTROPY ALWAYS INCREASES
∆G(sys) <0 (-ve)
NOTE: spontaneity is not related to kinetics (can be fast or slow, eg. diamond to graphite) or enthalpy (can be endo/exo)
define “closed” system
no transfer of MATTER from system to surroundings
if a process is reversible and adiabatic, it is…
isentropic.
reversible: dS = ∂q/T
adiabatic: ∂q = 0.
hence dS = 0.
SFEE
Qin - Wout =
m * (∆h) + m * (∆ V^2) + m * (g∆z)
specific enthalpy, kinetic energy, potential energy.
