Lectures 4-7

Question 1

Internal Energy is…

Answer 1

Sum of all of the microscopic forms of energy

Question 2

Boundary work is…

Answer 2

Work associated with the system boundary changing shape

Question 3

Equation for boundary work

Answer 3

W b = P * change in V

Boundary W = pressure * change in volume

Question 4

The general equation for boundary work

Answer 4

W b = integral ( P dV )

Boundary W = integral (pressure * change in volume)

Question 5

Enthalpy combines…

Denoted by letter…

Answer 5

Internal energy and Boundary work

H

Question 6

Enthalpy should be used for systems with a …

Answer 6

CHANGING volume

Question 7

On the other hand, internal energy should be used for systems with a…

Answer 7

FIXED volume

Question 8

Base equation of enthalpy

Answer 8

H = U + W b

Enthalpy = internal energy + Boundary work

Question 9

Equation for enthalpy subbing in for the Boundary work equation

Answer 9

H = U + PV

Enthalpy = Internal energy + (pressure * volume)

Question 10

First Law of Thermodynamics

Answer 10

Energy can neither be created or destroyed; it can only change forms

Question 11

An energy balance is when you …

Answer 11

find the difference in the sums of all the energy going into the system as well as those leaving the system.

Question 12

When carrying out an energy balance equation, we must remember to account for the energy associated with

Answer 12

mass

Question 13

When considering a stationary system energy balance equation, what can we assume as 0… This leaves only —, — and — to consider.

Answer 13

Kinetic and all potential energies

Mass, work and heat

Question 14

What interactions affect the energy content of a control volume/system?

Answer 14

As well as mass flow, heat and work

Question 15

When analysing a closed system what term can we remove from the energy balance equation

Answer 15

mass term as it is a closed system where no mass crosses the system boundary

Question 16

Closed system energy balance equation is

Answer 16

E system = Q net + W net

E system = change in U (change in internal energy)

as change in U = Q net + W net (net thermal energy and net work done)

Question 17

When a system runs in a cycle, what must return to its original state

Answer 17

The working fluid

Question 18

Efficiency in terms of a system measures what

Answer 18

how well an energy transfer or conversion has been carried out

Question 19

Specific heat capacity is defined as

Answer 19

the amount of energy required to raise the temperature of a unit mass of substance by one degree

Question 20

In thermo module, the two types of specific heat are

Answer 20

c v (constant volume) and c p (constant pressure)

Question 21

For solids and vapours are there two different values for specific heat?

Answer 21

No

Question 22

State specific heat capacity at constant volume

Answer 22

The amount of energy required to raise the temperature of a unit mass by 1K (or 1 degree C) with the volume being held constant.

Question 23

Equation for specific heat capacity at constant volume, to derivation of final equation using the 1st Law of Thermodynamics

Answer 23

1. c v = ( change in q / change in T ) v
2. 1st law of thermo Q 1-2 = U2 - U1 + W 1-2
3. Work term would be zero as the volume stays constant with NO boundary work so Q 1-2 = U2 - U1 (+ 0)
4. So change in q = change in u (q is thermal energy and u is internal energy)
5. c v = ( change in u / change in T ) v

Question 24

What are the units for specific heat cap at constant vol

Answer 24

kJ/kg・K