Scales of Measurement Celsius scale based on where water freezes 0 C and where water boils 100 C Kelvin scale based on the movement of particles Absolute Zero At 0 K all particle movement has ceased ID: 304798
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Slide1
Heat and Heat TransferSlide2
Scales of Measurement
Celsius scale – based on where water freezes (0
C) and where water boils (100
C)
Kelvin scale – based on the movement of particles
Slide3
Absolute Zero
At 0 K, all particle movement has ceased
It is impossible to have a temperature lower than 0 K
0 K = -273
C
Slide4
T
C
=5/9 (T
F
-32º)
T
F
= TC9/5+32ºTK= TC+273.15
0
ºC
273 K
10
ºC
283 K
20
ºC
293 K
30
ºC
40
ºC
50
ºC
303 K
313 K
323 KSlide5
Kinetic-Molecular Theory
The faster particles move, the greater the kinetic energy or thermal energy. Slide6
Definitions
Temperature
–average kinetic energy of the particles in a substance
Thermometers measure temperature
Heat
– amount of energy transferred
Slide7
Thermal equilibrium
Energy will always travel from an area of higher energy to an area of lower energy.
Slide8
Thermal Equilibrium, cont.
Two substances with different energies transfer energy (higher
lower)
until their energies are equal.
This point is “thermal equilibrium”.Slide9
Heat transfer
Conduction: molecular agitation; no motion as a whole
Convection: mass motion of a fluid
Radiation: emission of EM waves, no medium neededSlide10
Conduction
As materials are heated, electrons gain thermal energy which means they move faster.
As the electrons in a substance collide, the energy is transferred to surrounding electrons.
The actual molecules do not change places.Slide11
Convection
Heating occurs due to the motion of a fluid.
When a fluid is heated, it becomes less dense and rises. The cooler air is more dense and circulates to the bottom where it is heated and begins the process again.
Slide12
Radiation
Radiation does not require a medium to transmit energy. This type of energy is called radiant energy and it travels in electromagnetic waves.
High temperatures emit short wavelengths whereas low temperatures emit long wavelengths.
Slide13
Specific Heat
Amount of energy that must be added to the material to raise the temperature of a unit mass one temperature unit.
The units of specific heat are J/kg
·
K or J/kg·°CSlide14
Specific Heat Formula
Q = mC
T
Q = mC (
T
final
– Tinitial)Q = Heat (J)m = mass (kg)C = Specific heat (J/kg·K or J/kg·°C)T = change in temperature (K or °C)Slide15
Example #1:
A 0.400 kg block of iron is heated from 295 K to 325 K. How much heat had to be transferred to the iron if the specific heat of iron is
450 J/ kg·K?
Slide16
Example #1:
Q = mC
T
Q = (0.400 kg)(450 J/ kg
·
K)(325-295 K)
Q = (0.400 kg)(450 J/ kg·K)(30 K)Q = 5400 JSlide17
Law of Conservation of Energy
Energy lost by one object must be equal to the amount gained by another object.
Energy lost = - Energy gained
m
A
C
A
TA = -mBCBTBSlide18
Example #2:
A container has 0.50 kg of water at 15
C. A 0.040 kg block of zinc at 115
C is placed in the water. What is the final temperature of the system? (C
zinc
= 388 J/kg·C and Cwater = 4180 J/kg·C)Slide19
Example #2:
m
A
C
A
T
A = -mBCBTB(0.5)(4180)(Tf -15)= - (.04)(388)(Tf -115)2090(Tf -15) = - 15.52(Tf -115)2090 Tf - 31350 = -15.52 T
f + 1784.82105.52 Tf = 33134.8
Tf = 15.74 ºC