Temperature and thermal equilibrium Hot Cold
Jan 12, 2016
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