Lecture 1

Question 1

only gases have different

Answer 1

cp and cv values as solids and liquids are incompressible so cp and cv are the same

Question 2

extensive vs intensive

Answer 2

intensive means independent of mass

Question 3

open system

Answer 3

can exchange mass and energy

Question 4

closed system

Answer 4

can exchange energy with surroundings but not mass

Question 5

isolated system

Answer 5

cannot exchange mass or energy

Question 6

Cp

Answer 6

heat capacity at constant pressure (doesnt actually vary much with pressure)

Question 7

Cv

Answer 7

heat capacity at constant volume doesnt vary much with volume

Question 8

change in enthalpy =

Answer 8

Cp*changein temperature

Question 9

change in internal energy

Answer 9

Cv * change in temperature

Question 10

closed system important variable

Answer 10

internal energy
to calculate use Cv for U
dont worry about change in volume

Question 11

open system important variable

Answer 11

enthalpy
calculate use Cp for H
dont worry about change in pressure

Question 12

zeroth law of thermodynamics

Answer 12

If A is in thermal equilibrium with B and B is in thermal equilibrium with C then A and C are in thermal equilibrium.
all same temp no temp flows between them

Question 13

adiabatic process

Answer 13

Adiabatic means no heat flows into or out of the system.

Question 14

adiabatic practical examples

Answer 14

situation occurs so fast that heat cannot escape fast enough to make a difference ie piston cylinder

Question 15

adiabatic options

Answer 15

perfectly insulated system (never happens)

boundary at same temp as the system

Question 16

internal energy

Answer 16

total energy of an ideal gas molecule

Question 17

equation of state

Answer 17

pV = nRuT

Question 18

portion of internal energy associated with kinetic energy of the molecules called

Answer 18

sensible energy

Question 19

heat is

Answer 19

form of energy that is transferred between two systems (or a system and its surroundings) by virtue of a temperature difference.

Question 20

work is

Answer 20

Work is the energy transfer associated with a force acting through a distance

Question 21

work is path dependent

Answer 21

see powerpoint

Question 22

heat flowing from the surroundings into the system is taken as

Answer 22

positive

Question 23

work done by the system on the surroundings is taken as

Answer 23

positive

Question 24

change in energy

Answer 24

heat in - work out

Question 25

enthalpy =

Answer 25

internal energy + work

Question 26

viscosity

Answer 26

shear stress/shear strain Pa s or kg m^-1 s^-1

Question 27

internal energy

Answer 27

sums of molecular energy, rotational, translational, vibrational energy of molecules; extensive energy, J or kJ

Question 28

enthalpy

Answer 28

H=U+PV (internal energy+ pressure x volume ); kJ, extensive property

Question 29

What is meant by the phase of a system

Answer 29

A phase is where the properties of a system vary smoothly (with temperature for example), or they are essentially uniform. Water as a liquid is one phase, ice another phase. At the transition from liquid to ice the properties change.

Question 30

What is meant by “the state” of a system?

Answer 30

“At a given state, all the properties of a system have fixed values.”

The state is essentially a measure of the specific energy of a system. A system can change state, without changing phase. Heating water (at 1 bar) from 10 to 30°C changes its state as the thermodynamic variables describing it change but it remains a liquid. Heating to 120°C changes both phase (liquid to gas) and state.

Question 31

c. What is the minimum number of independent properties required to completely describe the state of a system? Are they intensive or extensive or either type of properties

Answer 31

Two intensive properties is the minimum required. For example for an idea gas, the equation of state is pV=nRuT :p is intensive V/n is intensive or p and T etc.

Question 32

difference between heat and work

Answer 32

Heat is the form of energy that is transferred between two systems or a system and its surroundings by virtue of a temperature difference.
Work is the energy transfer associated with a force acting at a distance.
Both have the same units J but more commonly due to the sizes of the changes we will discussing we will use kJ

Question 33

energy to vaporise =

Answer 33

hf - hg (must be in the same state)

Question 34

thermodynamic equilibrium

Answer 34

a system that maintains thermal, mechanical, phase, and chemical equilibrium.

Question 35

Isothermal process

Answer 35

constant temp

Question 36

Incompressible flow

Answer 36

flow with insignificant density changes