Thermal Physics

Question 1

What are the three laws of thermodynamics?

Answer 1

Zeroth law, Frist law, Second law

Question 2

What is Zeroth law?

Answer 2

If A and B are in thermal equilibrium with C then A and B are in thermal equilibrium with each other

Question 3

What is First law?

Answer 3

ΔE=Q-W (ΔE is net change in total energy, Q is heat added to the system, W is work doen by the system)

Question 4

What is Second law?

Answer 4

In all spontaneous processes, the entropy of the universe increases i.e. entropy always increases with time

Question 5

What is entropy?

Answer 5

The degree of disorder or randomness in a system

Question 6

What is a system?

Answer 6

A portion of the Universe with certain measurable
quantities (such as pressure or volume) which determine the equilibrium state of
the system

Question 7

What is an isolated system?

Answer 7

A system that does not interact with its surroundings by exchanging heat
energy, mechanical energy or material

Question 8

What is a closed system?

Answer 8

A system in which energy but not material can be exchanged

Question 9

What is am adiabatic wall?

Answer 9

The system is thermally isolated and

only mechanical energy (not heat) can be exchanged with the surroundings (e.g. a vacuum flask)

Question 10

What is a diathermal wall?

Answer 10

Heat exchange is permitted; systems

connected by a diathermal wall are in thermal contact (e.g. a metal wall)

Question 11

What does equilibrium mean?

Answer 11

All bulk physical properties are uniform throughout the system, they are time-independent

Question 12

What does macroscopic mean?

Answer 12

Large-scale or bulk properties of a gas (e.g.: P, V, T)

Question 13

What does microscopic mean?

Answer 13

Properties on the atomic-level (e.g.: vrms, vmp.)

Question 14

What are state variables?

Answer 14

These define the state of a system

Question 15

What does intensive mean?

Answer 15

Independent of the size of the system

Question 16

Give 2 examples of intensive properties

Answer 16

pressure, tension

Question 17

What does extensive mean?

Answer 17

Proportional to the size of the system

Question 18

Give 2 examples of extensive properties

Answer 18

volume or length

Question 19

What are equilibrium states of thermodynamic systems determined by?

Answer 19

Suitable pairs of conjugate variables

Question 20

What is a pair of conjugate variables?

Answer 20

One variable will be intensive and the other extensive

Question 21

Give an example of pairs of conjugate variables for a gas and for a stretched wire

Answer 21

(P, V) for a gas. Or

(tension, length) for a stretched wire

Question 22

What dimensions does the product of all conjugate pairs have?

Answer 22

The dimentions of energy

Question 23

What is a function of state?

Answer 23

Any quantity which takes a unique value for each equilibrium state of a system

Question 24

Give an example of a state funtion

Answer 24

Internal energy U or entropy S

Question 25

What do functions of state depend on?

Answer 25

Only on the state itself and not on how that state was | produced

Question 26

Why is heat not a function of state?

Answer 26

Because it is associated with a transfer of energy between states

Question 27

What is heat (Q)?

Answer 27

The form of energy transferred between substances due to temperature differences between them

Question 28

What happens in terms of heat when two objects are NOT in thermal equilibrium?

Answer 28

Heat flows from the hotter object to the colder object until thermal equilibrium is reached

Question 29

What is temperature?

Answer 29

The property which determines whether or not a system is in thermal equilibrium with other systems

Question 30

What are is the condition for Thermal equilibrium?

Answer 30

same temperature

Question 31

What is the condition for Mechanical equilibrium?

Answer 31

no unbalanced forces acting

Question 32

What is the condition for Chemical equilibrium?

Answer 32

no chemical reactions occurring

Question 33

What do Non-uniformities in a system result in?

Answer 33

a gradient and, hence, momentum, heat | and / or matter flows until thermodynamic equilibrium is reached

Question 34

What are Consequences of Thermodynamic Equilibrium On a macroscopic level?

Answer 34

variables have constant values in time and space (i.e.: | throughout the system)

Question 35

What are Consequences of Thermodynamic Equilibrium On a microscopic level?

Answer 35

``` any process (e.g.: diffusion, collisions) must have an equal probability of going in the opposite direction ```

Question 36

What is the equation of state?

Answer 36

f(P, V, T) = 0

Question 37

What is an ideal gas?

Answer 37

A gas for which hydrostatic equilibrium holds. i.e.: the inward force of gravity balances the outward gas pressure

Question 38

What do we assume in an ideal gas?

Answer 38

that atoms or molecules are non-interacting and | point-like

Question 39

What is the equation of state with R = 8.31 J K^–1 mol^–1?

Answer 39

f(P, V, T) = PV – nRT = 0

Question 40

How would we write the equation of state with the boltzmann constant?

Answer 40

PV – nkBT = 0

Question 41

What is a non-ideal gas?

Answer 41

A gas which has molecules with a finite volume and as a consequence, intermolecular forces (which are attractive) must be considered

Question 42

What is The equation of state for a van der Waals gas?

Answer 42

f(P, V, T) = (P+(n^2a/V^2))(V-nB)-nRT=0

Question 43

What is An indicator diagram?

Answer 43

a graph of an intensive variable (e.g.: P) against its conjugate extensive variable (e.g.: V)

Question 44

What is an isotherm?

Answer 44

The continuous line between any two states (P, V) and (P',V') in thermal equilibrium with each other (they will beat the same temperature)

Question 45

Describe Isotherms for a van der Waals gas (3)

Answer 45

``` 1. The isotherms look the same for both gas types at high temperatures 2. The behaviour begins to change as temperatures drop 3. Below a critical temperature Tc a phase change occurs ```