1

A Macroscopic Description of Matter

Readings: Chapter 16

2

Solid, Liquid, Gas

-Solid has well-defined shape and well-defined surface.

Solid is (nearly) incompressible.

-Liquid has well-defined surface (not shape), It is

(nearly) incompressible.

- Gases are compressible. They occupy all volume.

3

Solid, Liquid, Gas: Density

-Density is defined as a ratio of the mass of the object and occupied volume

The mass of unit volume (1m x 1m x 1m)

Units:

m

V

3/kg m~gas liquid solid

ice water

The density of the ice is slightly less than water,

causing them to float. Roughly 9/10 of the iceberg is

below water.

4

Solid, Liquid, Gas: Density

5

At 4°C water expands on heating or cooling. This density maximum

together with the low ice density results in (i) the necessity that all of a

body of fresh water (not just its surface) is close to 4°C before any

freezing can occur, (ii) the freezing of rivers, lakes and oceans is from

the top down, so permitting survival of the bottom ecology.

water

0( )T C40

atmospheric pressure

6

1 mole (1 mol) of substance is an amount which contains basic

particles (atoms or molecules)

Avogadro’s number is the number of basic particles in 1 mole:

Solid, Liquid, Gas: Mole

236.02 10

23 16.02 10AN mol

If we know the number n of protons and neutrons in basic particles then we can find the mass of 1 mole:

27 231.661 10 6.02 10 0.001mole proton A

kg kg gm nm N n n n

mol mol mol

So, n is the molar mass (the mass of 1 mole in grams)

7

The number of protons and neutrons in atom

8

Temperature

Temperature is the measure of internal thermal energy

Different scale:

- Fahrenheit, F

- Celsius, C

- Kelvin, K - SI scale of temperature

0932

5F CT T

273K CT T 00 273C KExample:

Absolute zero:

00 273K C

The temperature (in K) can be only positive

9

Solid, Liquid, Gas: Phase Changes

10

Specific heat of a substance is related to its thermal energy.

Specific heat is defined as:

The amount of energy that raises the temperature of 1 kg of a substance by

1 K is called specific heat, c.

Heat: Specific Heat

Q Mc T

11

Phase Change: Solid, Liquid, and Gas

Phase change: change of thermal energy without a change in temperature

12

Phase Change: Solid, Liquid, and Gas

Phase change: change of thermal energy without a change in temperature

Specific Heat

13

Phase Change: Solid, Liquid, and Gas

Phase change: change of thermal energy without a change in temperature

Heat of transformation (L) : the amount of heat energy that causes 1 kg of

a substance to undergo a phase change.

Q ML

fQ ML

Heat of

Fusion

vQ MLHeat of

Vaporization

Heat of Fusion – the heat of

transformation between a solid

and a liquid

Heat of Vaporization – the heat

of transformation between a

liquid and a gas

14

Specific Heat

Substance

Latent Heat

FusionkJ/kg

MeltingPoint

°C

Latent Heat

Vaporization

kJ/kg

BoilingPoint

°C

Alcohol, ethyl

108 -114 855 78.3

Ammonia 339 -75 1369 -33.34

Carbon dioxide

184 -78 574 -57

Helium     21 -268.93

Hydrogen 58 -259 455 -253

Lead 24.5 372.3 871 1750

Nitrogen 25.7 -210 200 -196

Oxygen 13.9 -219 213 -183

Water 334 02260

(at 100oC)100

SubstanceSpecific Heat

J/kg/K

Water (0 oC to 100 oC) 4186

Methyl Alcohol 2549

Ice (-10 oC to 0 oC) 2093

Steam (100 oC) 2009

Benzene 1750

Wood (typical) 1674

Soil (typical) 1046

Air (50 oC) 1046

Aluminum 900

Marble 858

Glass (typical) 837

Iron/Steel 452

Heat of Transformation

15

Ideal Gas

16

Ideal Gas:

Ideal gas:

-no interactions between the atoms, (without interactions no phase transition to liquid phase)

-atom as a hard-sphere

-temperature will determine the average speed of atoms.

21 3

2 2atom Bm v k T

231.38 10B

Jk

K Boltzmann’s constant

17

Ideal-Gas Law

pV nRTp – gas pressure

V – gas volume (container volume)

T – gas temperature (in Kelvin!!)

n – the number of moles – this can be found as where M is

the mass of the gas and is the mole mass

R=8.31 J/mol K - universal gas constant

gas

B AR k N

molM mol

Mn

M

18

Ideal-Gas Processes

The state of the gas is determined by two parameters:

P and V or

P and T or

V and T

pV nRT

If we know P and V then we can find T :

pV diagram

19

Ideal-Gas Processes: Constant Volume Process

V = constant

pV nRT

nRp T

V

Isochoric process

20

Ideal-Gas Processes: Constant Pressure Process

p = constant

pV nRT

nRV T

p

Isobaric process

21

Ideal-Gas Processes: Constant Temperature Process

T = constant pV nRT1

p nRTV

Isothermal process

22

Example: Find , and if n = 3 mol2p 1V 3V

1 1 1pV nRT

1 2 200000p atm Pa

1 273 37 310T K

311

1

3 8.3 3100.04

200000

nRTV m

p

2 2 2p V nRT

1 273 657 930T K 3

2 1 0.04V V m

522

2

3 8.3 9305.8 10 5.8

0.04

nRTp Pa atm

V

23

Example: Find , and if n = 3 mol2p 1V 3V

3 3 3p V nRT

3 1 2 200000p p atm Pa

3 2 930T T K

333

3

3 8.3 9300.12

200000

nRTV m

p