Thermo

Question 1

Isolated systems?

Answer 1

Don’t allow transfer of mass or energy in or out

e.g. thermos flask

Question 2

Closed systems?

Answer 2

Allow transfer of energy in or out but mass remains constant
e.g. gas in a cylinder

Question 3

Open systems?

Answer 3

Mass and energy can be transferred in or out
e.g. centrifugal compressor

Question 4

Intensive properties?

Answer 4

Properties which are independent of mass/system size

Question 5

Examples of intensive properties

Answer 5

Temp, density, pressure, specific enthalpy

Question 6

Extensive properties?

Answer 6

Properties which are dependent/proportional to mass or system size

Can be converted to intensive by dividing one property by another e.g mass/vol = density
total energy/mass = specific energy

Question 7

Examples of extensive properties

Answer 7

Volume, internal energy, enthalpy

Question 8

State variables?

Answer 8

Describe state of the matter @ equilibrium

Independent of the path to reach them

Question 9

Examples of state variables

Answer 9

Temp, pressure, vol, entropy, mass

Question 10

Isothermal process?

Answer 10

System changes without temp changing

Remains in thermal equilibrium

e.g. refrigerator

Question 11

Isobaric process?

Answer 11

System changes without pressure changing

e.g. boiling water to steam

Question 12

Isocharic process?

Answer 12

System changes without volume changing

e.g. ideal Otto cycle / a pressure cooker

Question 13

Adiabatic process?

Answer 13

System changes without any heat or energy transfer occuring

e.g. piston in car engine

Question 14

Process functions?

Answer 14

Describe the route to move away from equilibrium, depend on path

Give finite amounts, rather than a change, when integrated

e.g. work, heat

Question 15

Zeroth law of thermo?

Answer 15

When two objects are separately in thermal equilibrium with a third, they are all in thermal equilibrium

Question 16

Examples of sources of potential energy within a system

Answer 16

-Attractive and repulsive forces
-Sub-molecular energy associated with nuclei and electrons e.g. bonds

Question 17

First law of thermo?

Answer 17

Energy can’t be created or destroyed

Question 18

How are irreversible and reversible processes shown on a PV plot?

Answer 18

-Irreversible are shown as a dashed line, as the intermediate steps between the initial and final states are not in equilibrium
-Reversible are a solid line as the system passes through a set of equilibrated states, but is generally a slow process

Question 19

What are irreversible processes?

Answer 19

Those which can’t return to a previously equilibrated state by simply reverting back to the original conditions

Question 20

What are reversible processes?

Answer 20

Those where you can move from one equilibrated stater to another (quasi-statically) by simply altering the conditions of the system

Question 21

What is the entropy change of any system and its surroundings, when considered together?

Answer 21

-Gives a positive value
-Approaches zero when the process approaches reversibility

Question 22

What is the 2nd law of thermo?

Answer 22

For an irreversible process the combined entropy of the system and environment will increase

Question 23

What are the 4 steps of a carnot cycle/engine

Answer 23

1) Isothermal process
2) Adiabatic process
3) Reverse isothermal process
4) Reverse adiabatic process

Question 24

What is a carnot engine

Answer 24

-A reversible engine, dS = 0`
-Able to create work
-If run backwards, it requires work (refrigeration)