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MS1016 - Thermodynamics of Materials > CH1 - First Law of Thermodynamics: Conservation of Energy > Flashcards

CH1 - First Law of Thermodynamics: Conservation of Energy Flashcards

Systems, State function and work, 1st law of thermodynamics, Enthalpy and steady state condition, Applications of 1st law and calculating enthalpy, Adiabatic flow and compression, Enthalpies of formation

1
Q

What is a system?

A

Designated boundary; comprising of any matter which we are interested in (any part of a physical universe)

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2
Q

What are conditions for a system?

A
  1. Must be separated from the rest of the universe with boundaries
  2. Contains particles in continual motion and interacting with each other
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3
Q

What is a closed system?

A

No matter enters or leaves (no movement of matter)

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4
Q

What is the extended/complete 1st law in differential form? (Account for energy in the equation)

A

δQ + δW = dU + d(PE) + d(KE)

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4
Q

What is an open system?

A

Matter may freely enter or leave

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5
Q

What is a quasi-static process?

A

Also known as a reversible process.

It is a thermodynamic process that occurs so slowly (i.e. under an infinitesimally small driving force) that the system remains in internal equilibrium throughout the entire process.

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5
Q

What are macroscopic properties?

A

Pressure, Temperature, Volume etc, affected by microstate

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6
Q

Examples of microscopic properties?

A

Atomic velocity & position, Brownian motion etc

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7
Q

What is the microstate of a system?

A

Defined by describing atomic/ molecular velocities and positions of the system at any point of time

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8
Q

Thermodynamic properties/ variables characterising the macrostate?

A

Pressure
Temperature
Volume
No of moles
Energy (Kinetic/ Potential energy)

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9
Q

If number of moles of various substances are known…?

A

ANY TWO of the thermodynamic variables is sufficient to specify the macrostate

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10
Q

What are the conditions for equilibrium?

A

If a system is undisturbed for a period, it will settle down until no further change occurs macroscopically

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11
Q

What are intensive properties?

A

Properties independent of the system size and amount of matter present

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12
Q

What are extensive properties?

A

Properties dependent on amount of matter present

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12
Q

What are macroscopic properties?

A

Macroscopic properties are things we can observe. (e.g. T, P, X, V, U)

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13
Q

What is a microstate?

A

Microstate describes the instantaneous velocity/position of atoms/molecules.

13
Q

What is the ideal gas equation?

A

PV = nRT

13
Q

If heat is GAINED by a system, is heat (Q) positive or negative?

A

Positive

14
Q

If heat is LOST by a system, is heat (Q) positive or negative?

A

Negative

15
Q

If work is done BY a system, is work (W) positive or negative?

A

Negative

16
Q

If work is done ON a system, is work (W) positive or negative?

A

Positive

17
Q

What are state functions?

(Hint: U, H, and S are state functions)

A

Change depends only on initial and final states of the system.

Hence dU, dH, and dS represent exact differentials.

18
Q

Derive δW = PdV in isobaric conditions

A

W = PV
δW = PdV + VdP
In isobaric conditions, dP = 0.
δW = PdV

19
Q

Express U as a state function with state variables P and V.

A

U = U (P, V)

20
Q

Specific internal energy

A

U_ = U/m

21
Q

Specific volume

A

V_ = V/m = 1/ρ

22
Q

Molar volume

A

V_ = V/mol

23
Q

Derive H = U + PV from 1st law and ideal gas equation. Assume isobaric process.

A

δW = PdV
∴ ΔU = Q - P(ΔV)
Q = ΔU + PΔV
(U₂ + PV₂) - (U₁ + PV₁) = Qₚ

Since the expression (U + PV) contains only thermodynamic state variables, the expression itself must be a thermodynamic state variable. This is called the enthalpy of the system.

H = U + PV
∴ Qₚ = H₂ - H₁ = ΔH
δQₚ = dH

24
Q

Define what is a “steady state” condition

A

ΔU = 0

A state or condition of a system or process that does not change (or changes only slightly) over time.

25
Q

What is heat capacity?

A

The amount of heat to be supplied to an object to produce a unit change in its temperature.

In constant volume:
Cᵥ = (δQ/dT)ᵥ = (δQᵥ/dTᵥ) = (∂U/∂T)ᵥ

In constant pressure:
Cₚ = (δQ/dT)ₚ = (δQₚ/dTₚ) = (∂H/∂T)ₚ

26
Q

What is adiabatic condition?

A

No thermal energy can pass through the boundary.

Since no heat can flow in or out of the system, δQ = 0.

27
Q

Recall the 1st law for steady state open systems

A

Q + W = ΣHₒ - ΣHᵢ

When using specific enthalpy where H_ = H/m :
Q + W = ΣH_ₒM_ₒ - ΣHᵢMᵢ

28
Q

What is isenthalpic condition?

A

Constant enthalpy.

ΔH = 0

29
Q

What is the Joule-Thomson expansion?

A

ηⱼₜ = (∂T/∂P)ₕ

30
Q

Derive Cₚ - Cᵥ = R

A
31
Q

Values of Cₚ for a monoatomic and diatomic ideal gas?

A

Monoatomic: (5/2)R
Diatomic: (7/2)R

32
Q

Values of Cᵥ for a monoatomic and diatomic ideal gas?

A

Monoatomic: (3/2)R
Diatomic: (5/2)R

33
Q

What is Hess’s Law?

A

MS1016 - Thermodynamics of Materials (8 decks)

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