18 Heat and the First Law of Thermodynamics • Heat Capacity and Specific Heat • Change of Phase and Latent Heat • Joule’s Experiment and the First Law of Thermodynamics • The Internal Energy of an Ideal Gas • Work and the PV Diagram for a Gas • Hk: 31, 37, 47, 51.
18 Heat and the First Law of Thermodynamics. Heat Capacity and Specific Heat Change of Phase and Latent Heat Joule’s Experiment and the First Law of Thermodynamics The Internal Energy of an Ideal Gas Work and the PV Diagram for a Gas Hk: 31, 37, 47, 51. Heat & Internal Energy. - PowerPoint PPT Presentation
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18 Heat and the First Law of Thermodynamics
• Heat Capacity and Specific Heat• Change of Phase and Latent Heat• Joule’s Experiment and the First Law of
Thermodynamics• The Internal Energy of an Ideal Gas• Work and the PV Diagram for a Gas• Hk: 31, 37, 47, 51.
Heat & Internal Energy
• heat is energy that flows due to temperature differences. SI Unit: joule
• internal energy is the total energy of an object in its center of mass reference frame
Specific Heat Capacity
• The amount of heat needed to raise 1kg by 1°C
• c = Q/mT SI Unit: J/kg·°C• m = mass receiving (or emitting) heat• T = temperature change• Q = mcT• /
Example: 300J of heat are added to 100grams of a substance. The temperature rises by 2.20 degrees C.
CkgJCkg
JTmQc
/1364
)20.2)(1.0(300
The specific heat of the substance is:
Example: Calorimetry
Other Heat & Energy Units:
JcallbftBtu 10542527781
Jcal 184.41
CalJkcal 141841
calJatmL 22.243.1011
Example Conversion
WBtuJ
sh
hBtu 35001054
3500000,12
A Gas Range is quoted (incorrectly) as “12,000 Btu”. The equivalent power for an Electric Range in watts is:
Solid/Liquid Transformation
• Melting• Heat in• KE breaks bonds• Molecules move• Liquid forms
• Freezing• Heat out• Molecules lose KE• Settle in one place• Solid forms
8
Energy in Phase Change
• Energy added: • solid liquid gas
• energy released: • gas liquid solid
Liquid/Gas Transformations
• Evaporation• Highest KE molecules
escape liquid from surface
• Evaporative cooling, e.g. sweat evaporates cooling your body
• Boiling• Highest KE molecules
form gas bubbles throughout
• Hot gas bubbles rise and escape at surface
• Liquid has passed heat out, e.g. simmering at constant temperature
Latent Heat• Energy needed to melt or vaporize 1kg
of a substance.• Latent Heat, L = Q/m. • Q = mL.• Example: 2.5kg of ice at 0.0°C melts
into 2.5kg of water at 0.0°C.
)/5.333)(5.2( kgkJkgmLQ f
kJ830
Joule’s Experiment confirmed the mechanical equivalent of heat.
1st Law Thermodynamics
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18-4 Internal Energy of Ideal Gas
• E-internal is proportional to the absolute temperature
• internal energy is in the kinetic energy of the molecules of the gas
• /
Work and the PV Diagram
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Viongas PdVW
it.on done be work topositivefor order in dV) (negative compressed bemust Gas