Entropy and the Second Law Flashcards
Describe the isothermal expansion of gas
Gas will flow from A to B until pressures are equal
U = 0 and H = 0
Heat flows in from the surroundings because the gas in A performs work on the gas in flask B
Describe thermal equilibrium
Two identical blocks of metal, one at Ta and the other at a lower temperature are brought into thermal contact and isolated
U = 0 as isolated system
Heat flow from A to B until blocks at equal temperature
What happens when a salt is added to water?
It will dissolve
Endothermic process(H > 0)
Solution cools down as heat absorbed
What occurs during
N204 (g) chemical equilibrium 2NO2 (g)
Spontaneous partial dissociation will occur
A highly endothermic event
What does the 2nd law imply?
Reactions can occur spontaneously even if they are disfavored in terms of the enthalpy changes
Spontaneous reaction moves towards a more disordered or more uniform state
The systems have lost some capacity for carrying out work
What are spontaneous changes always accompanied by?
Spontaneous changes are always accompanied by conversion of energy into a more disordered form
How does the entropy change during a spontaneous change?
Increases
What is the equation for entropy of a spontaneous process?
Stotal = Ssystem + Ssurroundings >0
How can entropy be expressed as differentials?
dS + dSsurroundings >0 (spontaneous, irreversible)
dS + dSsurroundings = 0 (equilibrium, reversible)
Give the work equation in terms of energy
Work = internal energy change - unavalible energy
dwreversible = dU - TdS
What is the work done for a reversible change?
A maximum
What stays constant regardless of how the change is carried out?
dU
Relate work done and heat change in reversible and irreversible reactions
dwreversible < dwirreversible
dqreversible > dqirreversible
During a reversible change, the system absorbs the maximum heat from its surrounding and does the maximum work
Observable spontaneous processes absorb less heat and do less work
Define entropy mathematically
deltaS = Sb - Sa = {dqrev/T where the upper bound is B and the lowe bouns is A
Differential equation when the system is at equilibrium
DS = dq/T
For an isolated system, dS = 0 so S is a constant’
For observable changes dS > 0
