exam 4 Flashcards
(25 cards)
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
