Temperature and thermal equilibrium

Hot Cold

Temperature is proportional to the kinetic energy of atoms and molecules: T~KE

Thermometer

Celsius, Fahrenheit, Kelvin

• Andres Celsius (1701-1744). Celsius’ scale relates to the freezing temperature of

water

• 0°C• and the boiling temperature of water

• 100°C

Daniel Fahrenheit

Daniel Gabriel Fahrenheit (1686-1736) 1709 - invented the alcohol thermometer 1714 - mercury thermometer

1724 - he introduced the temperature scale that bears his name - Fahrenheit Scale. Fahrenheit’s scale places the freezing point of water at 32ºF and the boiling at 212ºF. Exactly 180ºF apart.

• TF=9/5

In Russia schools are closed when temperatures reaches -35ºCWhat is the temperature in Fahrenheit's?

Lord Kelvin

• Kelvin’s scale related to the absolute zero – the point

where nothing else can be colder.

T (°C)

P(Pa)

-273.15

Conversion of T scales:

15.273 CTT

Thermal expansion

Thermal expansion

Thermal expansion• As temperature increases, the volume of the

object increases as well. The extent of thermal expansion is characterized by the coefficient of volume expansion

• CVEgases >>> CVEliquids >> CVEsolids

• ?? Why do train wheels rhythmically clink on the rails?

• ?? Why putting a jar under hot water makes it easier to open it?

• ?? When do you get more gas for your money: on a cold or a hot day?

Thermal equilibrium

T1 T2

T1<T3<T2

the state in which two bodies in contact with each other have identical temperatures

HEAT

The process by which energy is exchanged between objects because of a difference in their temperatures.

SI: [J] – joules

» James Joule

Conduction• the process whereby

energy is transferred directly through a material without any bulk motion of its particles.

• Conduction is mostly common in solids.

• Depending on whether materials conduct heat easily, they are divided into conductors and insulators.

Convection

process in which energy is transferred through a material with any bulk motion of its particles.

Convection is common in fluids

Radiation• the process in which energy is transferred

by means of electromagnetic waves.

Internal energy:

• the energy of a substance due to the random motions of its component particles (atoms and molecules) and equal to the total energy of those particles.

• U – internal energy

1 2

1) T1=T2

Compare U1 and U2

2) U1= U2,

Compare T1 and T2

21

21

Heat / Energy / Work units

Conservation of energy KE + PE + Work = const

Work – way to change U of the system

For an isolated system (no energy is lost )

0

0

UKEPE

WorkKEPE

If a total mass of 11.5 kg falls through 1.3 mand all of the ME is converted into U of water,by how much will U of water change? What will youobserve in the apparatus?

Specific Heat Capacity

Tm

Qc p

]Cº

[kg

Jc p

Cp shows how much heat is needed to change the temperature of 1 kg of substance by 1ºC

Examples:

• How much heat does it take to heat a 580 g aluminum pot (cp=0.92 J/gK) from 20ºC to 180º C?

• A lead bullet (cp=0.13 J/gK) going 460 m/s strikes a tree. If all the heat generated remains in the bullet, how much does its temperature rise?

3 States of 2H O

Phase Change

• The physical change of substance from one state (solid, liquid, or gas) to another at constant temperature and pressure

25T C

32.09 10p

Jc

kg K

pQ c m T

Q

Heat

Q(J)

T(°C)

0ºC

Q

0T C

53.3 10 /fL J kg

fQ L m

Q(J)0ºC

T(°C)

Q

34.19 10p

Jc

kg K

pQ c m T

Q(J)0ºC

T(°C)

At what point will the temperature stop rising?

Q(J)0ºC

T(°C)

100ºC

Q

100T C

62.26 10 /vL J kg vQ L m

Q(J)0ºC

T(°C)

100ºC

Heat of fusion – the energy per unit mass transferred in order to change a substance from solid to liquid or from liquid to solid at constant temperature and pressure

fQ L m

Heat of vaporization – the energy per unit mass transferred in order to change a substance from liquid to vapor or from vapor to liquid at constant temperature and pressure

fQ L m