Notes 2 Review

Question 1

What characterizes heat transfer?

Answer 1

Heat transfer is due to temperature difference SOLELY.
Moves energy from high to low temperatures- like pressure or voltage

Question 2

What characterizes work transfer?

Answer 2

Essentially is force applied for a distance.
Typically involves the change in volume of the system.
(Electrical energy is a notable exception)

Question 3

What is the sign convention for heat and work transfer?

Answer 3

Heat transfer:
positive if ADDED to the system
negative if LEAVING the system

Work tranfer:
positive if work done by the system on the surroundings (OUT)
negative if work done on the system by the surroundings (IN)

If system expands, work transfer positive
If system compresess, work transfer negative

Question 4

What is Work?

Answer 4

Force applied over a distace/displacement
Integral of F ds

Question 5

What is p dV work?

Answer 5

If equilibrium state statement applies, work is the integral of pressure over differential volume change. Integral of p DV.

Graphically, if we plot pressure on y-axis and volume on x-axis the Work is the area underneath the process curve connecting the start/end states

Question 6

What is a polytropic process?

Answer 6

When p * (V)^n = constant

Question 7

What are the types of mechanical energy?

Answer 7

Kinetic & Potential Energy

Question 8

What is Internal Energy?

Answer 8

Essentially the kinetic and potential energies of the systems molecules.
It is denoted by captical U

Question 9

Are Kinetic and Potential energy properties?
(Give reasoning why)

Answer 9

No.

Kinetic energy is velocity dependant, which is relative to referance frame- and thus breaks definition of thermo property.

Potential energy is dependant on height from datum, which is a relative reference frame and thus also breaks definition of thermo property.

Question 10

Is Internal Energy a property?

Answer 10

Yes!
At the molecular level, the potential energy is from the distance between molecules -which is absolute, regardless of reference frame.

Question 11

What is specific internal energy

Answer 11

U / m
Internal energy divided by mass

Any 2 intensive independant properties determine u

Question 12

What is the 1st Law of Thermodynamics?

Answer 12

Energy can neither be created or destroyed.

For a closed system: E_in - E_out = change in system energy

Q - W = ΔE = Δ( U + KE + PE )
Q - W = m * [(u_2 - u_1) + 0.5 * ((V_2)^2 - (V_1)^2) + g * (z_2 - z_1) ]

Question 13

What is the specific internal energy of ideal gas equal to?

Answer 13

u = C_v * T

gas specific heat * system temperature

C_v : Specific heat @ const volume [ J / (Kg * K)]
Heat Joules neccesary to raise 1 kg of gas 1 Kelvin

Question 14

What is Enthalpy?

Answer 14

The sum of the systems internal energy and the product of the systems volume and pressure.

H = U + p * Volume

Question 15

What is specific enthalpy?

Answer 15

h = H / m
System enthalpy (heat energy) normalized by mass

Question 16

For ideal gas, what is specific enthalpy equal to?

Answer 16

h = C_p * T
C_p: specific heat at constant pressure
T: Change in temperature

Question 17

How are C_v and C_p related?

Answer 17

C_p = C_v + R

Question 18

What is the specific heat ratio?

Answer 18

k = C_p / C_v

Question 19

What is the differential form of the first law?

Answer 19

𝛿Q – pdV = dU

𝛿Q + Vdp = dH

Question 20

What equation relates initial/final temperature, Volume, and pressures for a polytropic process in an ideal gas?

Answer 20

(T2/T1) = (V1/V2)^(n-1) = (P2/P1)^ ( [n - 1] / n )

Question 21

What is an Equilibrium process?

Answer 21

At every moment of the process the pressure and temperature of the system must be uniform.

Only equilibrium processes can be plotted on the P-V diagram

Easy test:
If process is reversable, process is equilibrius
Else, process is not equilibrius

Question 22

How do we evaluate work done by an irreversable processes?

Answer 22

Work_sys = ∫ 𝑝_surroundings *𝑑𝑉_surroundings
Work_sys = - ∫ 𝑝_boundary * 𝑑𝑉_system