exam 4 Flashcards
what is thermodynamics?
the study of energy and its transformation
what is entropy
heat transferred between the system and its surroundings
(a measure of randomness or disorder of a system)
1st law of thermodynamics
energy is neither created nor destroyed
Delta E= q+w
Delta E is change in internal energy
q is the heat absorbed by the system from the surrounding
w is work done
what happens when q is greater than 0
the system absorbs heat from surroundings
what happens when q is less than 0
system releases heat to the surroundings
what happens when w is greater than 0
surroundings are doing work on the system
what happens when w is less than 0
system is doing work on the surroundings
what are spontaneous processes
proceeds on its own without assistance
ice melting on a hot day; when you drop an egg and it is cracked
a process that is spontaneous in one direction is nonspontaneous in the opposite direction
what are non spontaneous processes
the reverse of a spontaneous processess
ex: breaking an egg and expecting it to go back together
reverse process
the change occurs in a way that the system + surroundings can be restored to their original state by EXACTLY reversing the change (the change has to be very small)
irreversible process
cannot simply be reversed to restore the system + surroundings to its original state, you have to change something in the system to restore it back to its original state
what is the second law of thermodynamics
-entropy always increases; the reason why you cannot unscramble an egg; chaos moves towards more chaos
Delta S= qrev/T
qrev is the amount of heat added reversibly to the system
- any irreversible process results in an increase in total entropy whereas any reversible process results in no overall change in entropy
isothermal process (constant T)
Delta S for phase changes
DeltaS fusion = qrev/T = DeltaH fusion / T
entropy change; constant temperature
Delta S = entropy ; qrev = heat transferred in a reversible process at constant T
Delta H units are kj/mol
reversible process equation
Delta S univ= Delta S System + Delta S surroundings = 0
irreversible process equation
Delta S univ= Delta S sys+ Delta S surr > 0
how can you increase entropy
- increase number of moles
- increase volume
- increase with temp
- increase when gases form from liquid to solids
- liquid or solutions form solids
- number of gas molecules increase during a chemical rxn
third law of thermodynamics
the entropy of a pure crystallite substance at absolute zero
K if we lower T, we slow down all processes
standard state = 298K
S knot
standard molar entropy ; units J/mol-K
gibbs free energy equation
spontaneous process that result in a positive in the systematic entropy are always exothermic
Delta G= Delta H^o - T(Delta S^o)
T is 298K ; Delta H change in enthalpy from reactants to products ; Delta S is change in entropy disorder
gibbs free energy Delta G relations
Delta G < 0 rxn is spontaneous in a forward direction
Delta G > 0 rxn is non spontaneous in forward direction
Delta G = 0 rxn is at equilibrium
free energy + temp
Delta G = Delta H + (-T Delta S)
Delta H is enthalpy
-T Delta S is entropy
Delta H < O and Delta S > 0
spontaneous at all T
Delta G < 0
Delta H > 0 and Delta S > 0
- spontaneous at increase T
- non spontaneous at decrease T
Delta H < 0 and Delta S < 0
- spontaneous at decrease T
- non spontaneous at increase T
Delta H > 0 and Delta S < 0
nonspontaneous at all T
Delta G > 0
