Thermal Physics

Question 1

States/Phases of Matter (Solid, Liquid, Gas)

Answer 1

Solid: molecules are closely packed, held together by strong bond, and vibrate about their fixed positions

Liquids: molecules are loosely packed, held together by weak bonds, and glide around each other

Gases: molecules are free tom ove about, they have no bonds between them, and they move randomly

No matter the state, some movt involved b/c molecules moving around and KE dependent on speed (not moving at same rate, so KE differs, and thermometer can;t measure for each of them, so takes avg.)

Question 2

Temperature

Answer 2

Measure of the avg KE of the particles in a substance
Unit: K (SI) or degrees C (we’re not dealing w/ degrees F b/c conversions would become complex)

Directly proportional to the KE of the molecules

If an object is heated, the KE of the molecules increases, resulting in increased temp

Measured using thermometer (and the two scales we’re going to use are K and degrees C)

K = degrees C + 273

Each scale (liquid or gas volume) varies linearly (at a constant pace) w/ the temp of the substance being measured, based on some physical properties such as expansions, contractions, etc.

Steam point is boiling point; ice point is freezing point

Question 3

Absolute Temp

Answer 3

Temp of an object when it is in a state of lowest energy possible (0 KE)

Equals -273 degrees C or 0 K

Hypothetical (cannot be reached)

Question 4

Heat (Thermal Energy [Q])

Answer 4

Energy transferred from oneo abject to another due to temp difference

Is a form of energy, but temp is not

= mcAT

Unit: Joules

Always from hot to cold

Temp determines the direction of heat flow

Question 5

KE (Molecular Level)

Answer 5

Energy due to random motion of molecules

Question 6

Potential Energy

Answer 6

Energy due to the intermolecular forces between the molecules of a substance

Question 7

Internal Energy

Answer 7

The total molecular PE + the total random KE of the molecules (don’t just say total energy: you could be incolcing other forms of energy)

Note:

Heating a substance increases its internal energy b/c the KE increases

A large material has more IE at the same temp (m increases, and Q is directly proportional, so…)

PE is affected when changing phases

Question 8

Heat Capacity (C)

Answer 8

Amt of thermal energy (heat) needed to raise the temp of an object by 1 K or 1 degree C

= Q/AT

Unit: J/K or J/degrees C

Question 9

Specific Heat Capacity (c)

Answer 9

Thermal energy (heat) needed to raise the temp of 1 kg of an object by 1 K or 1 degree C (difference will be the same)

= q/mAT

Unit: J/kg/K or J/kgdeg

NOTE:

Each substance has its unique c
The c of an object depends on masses and the type of material (if Q is constant)

Specific means per 1 kg

Water has a high SHC (4200): reason for being a universal cooling agent (takes a lot of heat/energy for the temp to rise)

Cha

SHC of ex. ice same as SHC of water

Question 10

Relating c to Power

Answer 10

*See notebook for formula

A graph of P vs mc has a slope of AT/t ot vice versa

Question 11

Measurement of SHC

Answer 11

Two methods: calorimetry/mixture and electrical

Question 12

Calorimetry/Mixture (b/c same for liquids)

Answer 12

Involves using the known SHC of a substance (water) to find the SHC of an unknown substance

If no energy is lost to the surroundings (ideal), energy gained by cold substance = energy lost by hot (mcAT = mcAT)—Law of Conservation of Energy

NOTE: in Physics, we go w/ AT = higher T - lower T

This loss of heat means that the initial temp of the object being transferred would be less, resulting in larger heat capacity

So, w/ calorimetry, source of error is loss of heat to surroundings b/c of transfer process

Question 13

Electrical

Answer 13

IVt = mcAT

Sources of error: loss of thermal energy from the apparatus; the container for the substance and the heater will also be warmed up; and it will take some time for the energy to be shared uniformly through the substance

*See note for formula

Question 14

Phase Change

Answer 14

This is a change of matter from one state to another

Energy is added/removed for a phase change to occur: this energy is only used for breaking/making bonds between the molecules (PE is affected)

Therefore, no temp is involved, as KE stays constant

Question 15

Specific Latent Heat (L)

Answer 15

Specific (per 1 kg), latent (temp not changing, but something happening).

Energy added/removed per unit mass during a phase change at constant temp.

= Q/m
Q = mL

Unit: J/kg

Since Qgain = Qloss
mcAT (ice cubes before they started melting) = mL (when water is freezing and has frozen/mixture of ice and water/whichever one is undergoing phase change [one going w/ mL as soon as it begins])

(ex. w/ ice cubes)

mcAT (water [when you have water, always assumed that temp has increased: AT would be 15 between original and present]) = mL (beginning to melt at 0 degrees C) + mcAT (before they start [ice cubes at -10])

Pt
IVt = mL

Two types of latent heat: latent heat of vaporization and latent heat of fusion

NOTE:
When solving problems that involve the melting of ice using heat, all the stages must be considered.

Question 16

Latent Heat of Vaporization

Answer 16

Heat added/removed when a unit mass of substance changes from liquid to gas/gas to liquid at constant temp

Question 17

Latent Heat of Fusion

Answer 17

Heat added/removed when a unit mass of substance melts/freezes respectively at constant temp

*NOTE: Specific latent heat of vaporization (by the time you’re here, you’ll have added a lot) > that of fusion b/c increase in separation of molecules is greater during vaporization than during melting (more energy required [breaking those bonds requires energy])

Question 18

Phase Change Curves of Ice

Answer 18

For heating, staircase w/ temp on y (-4, 0, 11) and Q or t on x: starts w/ ice only then passes through stages (mixtures in between [where it’s both]).

NOTE:

At any point, either KE or PE is increasing (never both), and graph can also be T vs. time (power/electricity [Pt = Q])

For cooling, staircase going downward (start over 100), same labels (end on x-axis).

Question 19

Pressure (P)

Answer 19

For gases, a measure of applied force of the molecules per unit area.

= Force/Area

Per unit area, area of walls, force w/ which they hit the walls.

Force is from collision of molecules w/ the wall (point molecules, so really small: wall has area). Only defined w/ respect to walls of container (point, so we don’t consider area around molecule [don’t consider collisions between b/c too small]).

Question 20

Equation of State of an Ideal Gas

Answer 20

PV = nRT

*w/ ideal gases, temp must be in Kelvin

Question 21

Ideal Gas Laws

Answer 21

Explain the behaviour of ideal gases. They include: Boyle’s Law, Charles’ Law, and the Pressure Law.

Concern temp, pressure, vol: one held constant in each law.

Question 22

Boyle’s Law

Answer 22

At constant temp, pressure inversely proportional to vol.

P directly proportional to 1/V
V = constant
P1V1 = P2V2

Graph of P vs. V is a downward slopping curve; curve of P vs. 1/V is a straight line going upward (passes through origin).

Question 23

Charles’ Law

Answer 23

At constant pressure, vol directly proportional to temp.

V directly proportional to T
V/T = constant
V1/T1 = V2/T2

V vs. T (K) linear and goign upward. V vs. T (degrees C) also straight line and going upward, but intercept origin behind y-axis at -273 (line dashed after pass y-axis).

Question 24

Pressure Law

Answer 24

At constant vol, temp directly proportional to pressure.

P directly proportional to T
P/T = constant
P1/T1 = P2/T2

*Graphs same as for Charles’ Law

Question 25

Kinetic Model of an Ideal Gas

Answer 25

Includes the following assumptions:

1. Molecules are point molecules
2. No forces of interaction between molecules (except during contact [when they collide w/ each other])
3. Motion of molecules is random
4. Collision between molecules is elastic (no energy lost)
5. Molecules obey all Newton’s Laws of Motion
6. Gravity if ignored (molecules assumed not to have masses)

NOTE:

For ideal gases, IE only equal to KE (no forces between molecules).

The pressure produced by the molecules is only due to their collisions w/ walls of container.

Question 26

Mole

Answer 26

Defined as # of particles in 12g of a carbon-12 (mass # [only applies to this isotope of C]).

One mole of any substance = Avogadro’s constant particles of that substance.

n = N (# of particles in substance)/NA (Avogadro’s constant)

Question 27

Molar Mass

Answer 27

Defined as the mass (g) of one mole of a substance.

If an element has mass # A, molar mass will be A grams.

ex. He has one of 4 g
H20 = 18 g

Question 28

Difference Between Real and Ideal Gases

Answer 28

Real gases can be liquified (ex. N2 at low temp), but ideal can’t ever (would require strengthening of bonds, which they don’t have).

Forces exist between molecules of real, but none do for ideal.

Real don’t obey PV = nRT for all values of P, V, and T (can at times, but there are some factors you have to put in place, but ideal do at all P, V, T values.

Real don’t obey gas laws at all P, V, T values (not all [ykwim]), but ideal do.

Question 29

Conditions Under Which a Real Gas Approximates an Ideal Gas

Answer 29

1. Low pressure (bigger container)
2. High temp (further away)
3. Low density

Question 30

Boltzmann Equation

Answer 30

*See in note…

NOTE:

Bar means avg.

See Boltzmann equation in note (KB = R/NA)

An ideal gas has only KE (no PE), so IE (U) = thing for avg. KE

N is the # of particles in a substance (there b/c now considering all particles of substance).

Use Boltzmann constant and PV = nRT to get U = 3/2PV