Week 1 Lecture 1 Basic Concepts

Question 1

Name & define three type of systems

Answer 1

1. Open - everything can leave
2. Isolated - nothing can leave
3. Closed - matter can’t leave but energy can (inc. thermal energy)

Question 2

Name & define three types of properties of a system

Answer 2

1. Extensive - depend on the size of the system
2. Intensive - independent of the size of the system
3. Specific - extensive properties divided by mass (lowercase)

Question 3

What is an independent property?

Answer 3

One that can be varies while the other property is held constant

Question 4

Define phase (in thermodynamics)

Answer 4

A region of space where matter is static in it’s properties - e.g done mixing ect.

Question 5

Define thermodynamic equilibrium

Answer 5

All three types of equilibrium present:

1. Thermal equilibrium - no temperature difference between system & it’s surroundings
2. Mechanical equilibrium - forces are balanced
3. Material equilibrium - means phase & reaction eq (i.e materials are done mixing & reacting or ‘transport’ & ‘ converting species’)

Question 6

Define process

Answer 6

A change that a system undergoes from one equilibriums state to another (via process paths)

Question 7

Define quasi-equilibrium

Answer 7

Literally an ‘almost’ equilibrium: when a process is slow enough the conditions of the system can be assumed to be (approx.) constant

Question 8

What is the Celsius scale based off of?

Answer 8

The boiling point and freezing point of water

Question 9

How is absolute zero found?

Answer 9

1. By saying some quantity is proportional to temperature
2. Finding the constant in terms of a known point in Kelvin (triple point of water)
3. Plotting values on a graph & extrapolating back

Question 10

Can anything be equal to absolute zero?

Answer 10

No; it can only tend towards it (because nothing is ever ideal)

Question 11

What is the oth law of thermodynamics?

Answer 11

It’s about implied thermodynamic equilibrium; “Went two objects are separately in thermodynamic equilibrium and with a third object, they are in equilibrium with each other”

Question 12

Name three pressure equations

Answer 12

1. P=f/a
2. P=\roh gh and integral form from modelling layers of fluid
3. The aeroplane pressure equation (pressure at an altitude exponential equation) - p=p_0e^{-GPE/KbT}

Question 13

Name & define two types of pressure

Answer 13

1. Absolute pressure - measured relative to vacuum (as is anything ‘absolute’)
2. Gauge pressure - measured relative to atmosphere (what you would see on a pressure gauge)

Question 14

Define energy

Answer 14

Ability to do work (where total energy is sum of micro and macroscopic energy)

Question 15

What is the difference between microscopic and macroscopic energy?

Answer 15

Microscopic energy is w.r.t the outside reference frame, macroscopic energy is w.r.t the molecules inside the system

Question 16

Define internal energy (of an ideal gas)

Answer 16

The sum of the KE and PE of gas molecules (where PE=U=U_trans+U_vib+U_rot+U_p)

Question 17

Why is potential energy for a molecule positive at (relatively) short distances?

Answer 17

Because repulsive forces do work to move the molecules apart

Question 18

Name ideal gas laws

Answer 18

Boyle - P, V
Charles - V, T
Avogadro - V, n
Gay Lussac - P, T

Question 19

When is the ideal gas law not valid?

Answer 19

At low temperatures and huge pressures

Question 20

What is a PVT plot?

Answer 20

A 3D plot of P vs V vs T (with an exponentially decreasing shape)

Question 21

Define partial pressure

Answer 21

It’s the pressure exerted by one gas in a mix of gasses if you took all of the other gases out (so in the same volume)

Question 22

Define Dalton’s Law of additive pressures & Amagat’s Law of additive volumes

Answer 22

For gas mixes you add the properties:

Dalton: the pressure of the gas mix is equal to the sum of the pressures of the individual gases

Amagat: the volume of the gas mix is equal to the sum of the volumes of the individual gases

Question 23

What is a mole fraction?

Answer 23

• For gas mixes the no. of moles of one gas / no. of moles of the total gas mix
• It’s the same as the number pressure fraction and volume fraction (as is unitless)

Question 24

State archimedes principle

Answer 24

The buoyant force is equal to the weight of the fluid displaced

Question 25

What is ‘apparent weight’ in the case of archimedes principle?

Answer 25

It’s the net downwards force a submersed object experiences when upthrust is taken into account