Heat and Thermo

Question 1

What is the zeroth law of thermodynamics?

Answer 1

This law is related to the existence and definition of temperature.

Question 2

What is the first law of thermodynamics?

Answer 2

This law is nothing more than a statement of the
conservation of energy. Basically it says that energy may be transferred into or out of a substance as either work or heat, but the total amount of energy remains constant.

Question 3

What is the second law of thermodynamics?

Answer 3

At a technical level the second law is a statement about something called entropy. From a microscopic point of view entropy is related to randomness, disorder and probability.

Question 4

What is temperature typically measured in and how do you convert it?

Answer 4

As you know, absolute zero is the coldest possible temperature. At absolute zero we have: Absolute zero: T = 0 K and TC = −273.15 ◦C

Question 5

Thermoscope vs Thermometer

Answer 5

A thermometer – which is an instrument which measures
the actual temperature of a substance

Question 6

Thermal Contact vs Thermally isolated vs Thermal Equalibrium

Answer 6

Then, two bodies are said to be in thermal contact with one another if heating just one of the bodies results in some macroscopic change in the other.
—————————————————————————————————-Two bodies are said to be thermally isolated from one another if
heating just one of the bodies results in no macroscopic change in the other.
—————————————————————————————————-
Two bodies are said to be in thermal equilibrium with one another if they are in thermal contact and no macroscopic changes occur in either body as time passes.

Question 7

Example of bodies A, B and Z

Answer 7

The zeroth law of thermodynamics: If bodies A and B are each in thermal equilibrium with a body Z, then A and B are in thermal equilibrium with each other. Thus we can say that two bodies have the same temperature if they are in thermal equilibrium with each other.

Question 8

Define Thermal Expansion

Answer 8

A well known property of almost all substances is their tendency to expand or grow in size as their temperature increases.

Question 9

What is the equation of linear expansion?

Answer 9

This equation describes how measured lengths change as the temperature changes: ∆L = Liα∆T linear expansion where α is a constant called the coefficient of linear expansion which has the units of K^−1 or ◦C ^−1.

Question 10

Example of Expansion using a ring/washer

Answer 10

If I increase the temperature of a ring or a washer, the hole gets bigger (not smaller as you might have guessed)

Question 11

What is the equation of volume expansion?

Answer 11

Used when computing volume changes of either liquids or solid bodies: ∆V = Viβ∆T, where β is a constant called the coefficient of volume expansion -> for a solid β = 3a

Question 12

What is the macroscopic state of a gas and what are the 3 state variables for gases?

Answer 12

The macroscopic state of a gas in thermal equilibrium is fully specified by its temperature, pressure and volume.

Temperature is denoted by the symbol T and has SI units of kelvin (K)

Pressure is denoted by the symbol p and has SI units of pascals or newtons per square metre (Pa or N m^−2)

Volume is is denoted by the symbol V and has SI units of cubic metres (m^3 )

Note: state variables are also known as s state parameters or thermodynamic variables.

Question 13

What are the 2 equation for ideal gas law/ideal gas equation?

Answer 13

pV = nRT, where R = 8.314 J K^−1 mol^−1 is called the universal gas constant and pV = N kT, where N is the number of gas particles (molecules or atoms) and k = 1.381 × 10−23 J K^−1 is called Boltzmann’s constant

Question 14

What is the equation of ideal gas law for a number of fixed particles?

Answer 14

pV/T = constant, typically written as p1V1 / T1 = p2V2 / T2

Question 15

What are the the three special cases of ideal gas law and their equations?

Answer 15

Boyles Law: The temperature and the number of particles of the gas doesn’t change throughout a process -> p1V1 = p2V2

Charles Law : The pressure and the number of particles of the gas doesn’t change throughout a process -> V1 / T1 = V2 / T2

Gay-Lussac’s law: The volume and the number of particles of the gas doesn’t change throughout a process ->p1 / T1 = p2 / T

Question 16

Why is it important that a gas must be in thermal equalibrium?

Answer 16

It is extremely important to understand that a gas must be in thermal equilibrium with its immediate surroundings for us to be able to talk about its pressure and temperature (and often volume too). This point was not stressed in the last section, but you need to be aware that p and T (and often V ) are not defined and cannot be measured if the gas is not in thermal equilibrium.

Question 17

What is a quasi-static process?

Answer 17

A process which is carried out so slowly that equilibrium is established at all in-between points. A quasi-static process carried out at constant temperature is called isothermal - If you connect together all points on a pV diagram which have the same temperature you will form a smooth curve called an isotherm,

Question 18

What is the kinetic theory of gases?

Answer 18

1. Newton’s laws apply to the gas particles.
2. The gas particles take up no volume (or are very tiny compared to the average distance between them) and are all identical.
3. The gas particles are constantly moving in random directions with a distribution of speeds that are independent of the direction of motion.
4. There are no attractive or repulsive forces acting between the gas particles or the surroundings. Except for collisions between other particles and the container walls the particles are free. They have no potential energy, just kinetic energy.
5. The gas particles undergo elastic collisions with each other and the container walls. No kinetic energy is lost in collisions.

Question 19

What is the formula for average transational kinetic energy?

Answer 19

K ave,trans = 1/2 mv^2 = 3/2 kT

Question 20

What is the formula for the thermal speed of the particle in terms of the gas temperature and particle mass?

Answer 20

vth = sqrt(3kT / m)

Question 21

Define ideal monatomic gas

Answer 21

An ideal gas consisting of point-like particles is said to be an ideal monatomic gas since the gas particles are just free atoms -> need to go over monatomic, diatomic and polyatomic…

Question 22

System, Evironment and Boundary

Answer 22

The part of the universe that we are interested in is called the system. Everything else around the system which may interact with it in some way is called the environment. The two dimensional surface which separates the system and the environment – whether it be real or imagined – is called the boundary.

Question 23

Define Thermodynamic Process

Answer 23

The procedure by which you change a system from one state to another state, where

Open system: A system without any restrictions. It can exchange energy and matter with its environment.

Closed system: A system which can exchange energy with its environment, but not matter.

Isolated system: A system which cannot interact in any way with its environment. No energy or matter can be exchanged with its environment.

Question 24

If temperature is Ts and enviroment is Te what a the 3 cases?

Answer 24

Case I: If Ts = Te then nothing happens. The system and environment are in thermal equilibrium.

Case II: If Ts > Te then the system is hotter than the environment and energy will be transferred from the system to the environment.

Case III: If Ts < Te then the system is colder than the environment and energy will be transferred from the environment to the system.

Question 25

Define heat

Answer 25

The energy transferred across the boundary between a system and its environment due to a temperature difference between them

Question 26

Define work

Answer 26

The energy transferred between a system and its environment due to a force acting over some displacement. The work done on a system is denoted by W and is measured in joules

Question 27

What is the formula for heat capacity and define it?

Answer 27

Q = C∆T = C(Tf − Ti), where Tf and Ti can be measured in either ◦C or K.
Heat capacity: The constant C of proportionality between the heat added and the temperature change
.

Question 28

What is the formula for specific heat and define it?

Answer 28

Q = mc∆T -> the temperature change of the sample; m is the mass of the sample; and c and is measured in J kg^−1 K ^ −1or J kg^−1 ◦C ^−1

Question 29

What is the formula for molar specfic heat?

Answer 29

Q = nC∆T -> Molar specific heat has SI units of J mol−1 K^−1 or J mol^−1 ◦C ^−1
.

Question 30

Define Phase change/transition

Answer 30

When the state of the substance (i.e. solid, liquid or gas) is altered

Whenever we heat something, the energy transferred can either go into: (i) increased kinetic energy of the consistent atoms or molecules, which registers as an increase in temperature; (ii) overcoming attractive forces between the molecules (i.e. increasing the potential energy shared between molecules), which registers as a phase transformation; or simultaneously both (i) and (ii)

For pure substances (i.e. substances made from only one type of molecule or atom), (i) or (ii) can occur but never both at the same time. That is, for pure substances the temperature remains constant as it changes phase. For substances which are mixtures (i.e. not pure) the behaviour can be far more complicated

Question 31

Define heat transformation and give its formula

Answer 31

Where L can be: Lf - heat of fusion or heat of melting. If the phase transformation is from liquid to gas, L is denoted by Lv and is called the heat of vaporization. If the phase transformation is from solid to gas, L is denoted by Ls and is called the heat of sublimation.

Question 32

Define phase diagram and its components (triple points and critical point)

Answer 32

A phase diagram is a simple means of showing under which conditions a substance undergoes phases transitions, and under which conditions the substance is a solid, liquid or gas.

The so-called triple point is a point on the plot under which all three phases are in thermal equilibrium

The so-called critical point is the point at which the boundary between the gas and liquid phases terminates

Question 33

What are all the typical transitions?

Answer 33

constant pressure melting: solid −→ liquid (f −→ g)
constant pressure freezing: liquid −→ solid (g −→ f)
constant pressure sublimation: solid −→ gas (e −→ d)
constant pressure deposition: gas −→ solid (d −→ e)
constant temperature boiling: liquid −→ gas (a −→ c)
constant pressure boiling: liquid −→ gas (a −→ b)
constant temperature condensing: gas −→ liquid (c −→ a)
constant pressure condensing: gas −→ liquid (b −→ a)

Question 34

Name the three heat transfer mechanisms

Answer 34

Energy is transported from a hotter body to a colder
body: conduction, convection and radiation

Question 35

What is thermal conduction and give its formula?

Answer 35

Is heat transfer by direct physical contact. More specifically, at the microscopic level, conduction is an energy transferred from more
energetic particles to less energetic particles via continuous collisions between them -> H = kA * ((Th − Tc) / L)

Question 36

Thermal conduction and thermal resistance

Answer 36

R = L / kA, which changes thermal conduction to H = (Th − Tc) / R

Question 37

What is convection and explain its steps/process?

Answer 37

1. The temperature of the part of the fluid in thermal contact with the hot substance
   will increase.
2. In getting hotter, the part of the fluid which is in thermal contact with the hot substance will thermally expand and decrease in density.
3. Having a lower density than the surrounding fluid, the hotter part of the fluid will rise due to buoyant forces.
4. Some of the surrounding cooler and more dense fluid will move in to replace the upward moving hotter fluid.
5. ## Some cooler fluid is now in thermal contact with the heat source and the process repeats.A macroscopic fluid flow will be established by convection which is called a convection current

Question 38

What is thermal radiation and give its formula

Answer 38

The final mechanism by which a system and its environment can exchange energy as heat is through electromagnetic radiation or light. Often the radiation exchanged between two bodies – or a system and its environment – due to a temperature difference is called thermal radiation -> Stefan-Boltzmann law: Pem = eσAT4

Here Pem is the total power emitted by the object in watts, σ = 5.67 × 10^−8 W m^−2 K&^−4 is the Stefan-Boltzmann constant and e is the emissivity of the object’s surface. The emissivity is a dimensionless number which has a value between 0 and 1 depending on the composition of the object. A perfect emitter – a so-called blackbody radiator – has an emissivity of e = 1

Question 39

Understanding work (done on and into)

Answer 39

we denote the work done on the system by the environment as W and the amount of heat transferred into the system from the environment by Q. Carefully note that in being defined this way, either of the two separate quantities Q and W might be positive, negative or zero depending on what exactly is going on.

Question 40

What is internal energy, the change in internal energy and the formlula for it?

Answer 40

if a system starts in an initial state i and has an initial internal energy Ui , and then has its state changed via some thermodynamic process and ends up in a final state f with a final internal energy Uf , then the change in internal energy of the system is:

∆U = Uf − Ui = Q + W

where Q is the heat transferred to the system and W the work done on the system during the process.

This is also the first law of thermodynamics

Question 41

What is the formula for infinitesimally small change in state?

Answer 41

dU = dQ + dW

Question 42

What is the formula for internal energy of a monatomic ideal gas?

Answer 42

U =3/2 * nRT

Question 43

What is the formula for monatomic ideal gas of any process

Answer 43

U =3/2 * nR∆T

Question 44

What is an important thing to remember any ideal gas

Answer 44

The internal energy of any ideal gas is a function only of its temperature and does not depend on any other variable. The internal energy of any ideal gas will not change if its temperature does not change.

Question 45

What is the formula for infinitesimal work done on a gas and total work done on a gas

Answer 45

Infinitesimal work done on a gas: dW = −pdV

Total work done on a gas: W = ∫dW = − Vf∫Vi pdV

Note that: The expressions above are always true for any gas as it undergoes any kind of quasi-static volume change

Question 46

Different paths – same change of internal energy

Answer 46

if we take a gas from a state i to f, the change of internal energy
is just ∆U = Uf − Ui. If we take this gas from i to f via different quasi-static paths, the change of internal energy will always be the same value no matter what the actual process is since internal energy is just the total energy stored in the gas. However, the work W done on the gas and the heat Q added to the gas do depend on the actual process or path taken. For this reason W and Q are said to be path-dependent quantities, whilst ∆U is said to be a path-independent quantity. THUS we say that heat and work are path-dependent quantities, whereas the internal energy is path-independent.

Question 47

What are the 5 process, their characteristics, the first law relationship, work and other relationships

Answer 47

REFER TO IMAGE -> isochoric, isobabaric, isothermal, adiabatic and free expansion

Question 48

Why is a quasi-static process reversable

Answer 48

An important feature of a quasi-static processes is that it is reversible: if a system starts in a state i and is taken through a quasi-static processes to a state f, we can easily reverse the process and take the system back from f to i. The reason that all quasi-static processes can be reversed is due to the fact that they are carried out by making small incremental steps, all of which are reversible.

The direction in which a thermodynamic process will spontaneously occur is determined by a quantity called entropy

Question 49

What happens when an irreversible process occurs within an isolated system?

Answer 49

If an irreversible process occurs within an isolated system, the entropy S of the system increases.

Question 50

What is the formula for entropy change?

Answer 50

∆S = Sf − Si = f∫i (dQ / T)

Question 51

What is the formula for infinitesimal entropy change?

Answer 51

dS = dQ/T

Question 52

Second Law of Thermodynamics and Entropy

Answer 52

The second law of thermodynamics: In an isolated system, the entropy cannot decrease. More specifically, if a process occurs in an isolated system, the entropy change of the system will be zero if the process is reversible, and will be greater than zero if irreversible.

In equation form the second law of thermodynamics states: for an isolated system undergoing some process the entropy change ∆S of the system is ∆S ≥ 0. Here the greater-than sign applies if the process is irreversible and the equal sign applies if the process is reversible.

Entropy may decrease for a system provided it is not isolated.

Question 53

Define Entropy

Answer 53

Entropy can be understood in a number of different ways which are closely related to one another: it can be thought of as a measure of the disorder of a system; or as a measure of how likely it is that a system will be in its current state; or as how much useful work a
system has to offer. The greater the entropy a system has, the more disordered the system is and the more probable its current state is.