Toni L1 Flashcards
(22 cards)
Define an isolated system
An isolated system cannot exchange energy or matter with its surroundings
Define a close system
A closed system can exchange energy exchange energy but cannot exchange matter with the surrounding
Define an open system
An open system can exchange both energy and matter with its surroundings
What is the first law of thermodynamics
The total change in internal energy of the system and its surroundings is zero
ΔUsys + ΔUsurr =0
For the first law of thermodynamics how do we calculate the total internal energy change for the system alone
ΔUsys = q + w
Where q is the heat absorbed by the system and w is the work done ON the system
Or dU = TdS - pdv
What is the second law of thermodynamics
In any thermodynamic process the total entropy of a closed system always increases
ΔSsys + ΔSsurr >/= 0
How can we rearrange the second law equation focusing on the contributions to the free energy change of the system
(ΔGsys)p,T = ΔHsys - TΔSsys </=0
What do the subscripts p,T indicate
The subscripts p,T indicate this applies at constant temperature and pressure
What is the gibbs free energy G defined as
G = H - TS
What is the enthalpy H defined as
H = U + pdv
What does internal energy depend on
Depends on composition, volume and temperature (state), it does not depend on how the system was prepared
Define state function
A state function is a property of a system that depends only on the current state of the system, not on the path or process taken to reach that state.
Give an example of a state function
Internal energy
Describe the internal energy change when a system goes from A to B
When a system goes from state A to state B, the internal energy change ΔU is just the difference between the internal energy of the final and initial state.
ΔU = Ub - Ua
Are heat and work state function
Heat and work are not state functions
How do we calculate work done on the gas
W = -PdV
Where p is pressure
And dv is the final volume - the initial volume
How do we calculate work done by the gas
Work done by the gas is the positive value
W= pdv
Describe the expansion of an ideal gas from V1 to V2 against external pressure
Expansion of an ideal gas from V1 to V2 against an external pressure equal to the gas’ own pressure, p.
Work done on the gas = -nRTln(v2/v1)
Why are state functions tablulated
can be used to calculate useful quantities for reactions by taking the difference between the values for the final state and the initial state.
How do we calculate the ΔGrxn, ΔSrxn, ΔHrxn
ΔGrxn = ΔGproducts - ΔGreactanrs
ΔSrxn = ΔSproducts - ΔSreactanrs
ΔHrxn = ΔHproducts - ΔHreactanrs
Define reversible process
A reversible process is one where the system and the surrounding can be returned to their initial state
What does the greater the external pressure lead to
The greater the work done
