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Quantifying Heat Energy

• Audio 0:03:56.456416
• The heat capacity of an object is proportional to the following:
  • Directly proportional to mass
  • The specific heat of the material
• The quantity of heat absorbed by an object can be determined if the following are known:
  • Mass
  • Specific heat capacity
  • Temperature change

Specific Heat Capacity

• Audio 0:05:10.723769
• Measure of a substance’s intrinsic ability to absorb heat.
• The specific heat capacity is the amount of heat energy required to raise the temperature of one gram of a substance 1 °C.
  • Cs
  • Units J/(g · °C)
• The molar heat capacity is the amount of heat energy required to raise the temperature of one mole of a substance 1 °C.
• 

Practice Problem:

Temperature Changes and Heat Capacity

• Audio 0:09:58.630420
• You find a pre-1982 penny in the snow. How much heat is absorbed as it warms from -8.0 °C to body temperature, 37.0 °C? Assume the penny is pure copper and has a mass of 3.10 g

Clicker 1

• Audio 0:12:20.872114
• A sample of copper absorbs 43.6 kJ of heat, resulting in a temperature rise of 75.0°C, determine the mass (in kg) of the copper sample if the specific heat capacity of copper is 0.385 J/g°C
  • A) 1.51
  • B) 6.62
  • C) 1.26
  • D) 7.94
  • E) 3.64

A

Heat Transfer and Final Temperature

• Audio 0:17:13.460079
• When two objects at different temperatures are placed in contact, heat flows from the material at the higher temperature to the material at the lower temperature.
• Heat flows until both materials reach the same final temperature.
• The amount of heat energy lost by the hot material equals the amount of heat gained by the cold material.
• If one is defined as our system, the other as surroundings then:
  • qsystem=-qsurroundings
  • qsys = -qsurr
• 

Thermal Energy Transfer

• Audio 0:19:06.599992
• A block of metal at 55 °C is added to water at 25 °C.
• Thermal energy transfers heat from the metal to the water.
• The exact final temperature depends on the following:
  • The mass of the metal
  • The mass of water
  • Specific heat capacities of the metal and of water
  • 
  • 

Practice Problem: Thermal Energy Transfer

• Audio 0:19:36.161583
• A 32.5 g cube of aluminum initially at 45.8 oC is submerged into 105.3 g of water at 15.4 oC. What is the final temperature? (Assume there is no heat lost)

Clicker 2

• Audio 0:26:13.227245
• A 43.9-g piece of copper (CCu= 0.385 J/g°C) at 135.0°C is plunged into 254 g of water at 39.0°C. Assuming that no heat is lost to the surroundings, what will the final temperature of the system be?
  • A) 100.0°C
  • B) 40.5°C
  • C) 62.5°C
  • D) 87.0°C
  • E) 53.1°C

B

Pressure–Volume Work

• Audio 0:33:15.662283
• PV work is work caused by a volume change against an external pressure.
• When gases expand, ΔV is positive, but the system is doing work on the surroundings, so wgas is negative.
• As long as the external pressure is kept constant, w = –PΔV.
  • Workgas = External Pressure × Change in Volumegas
• To convert the units to joules, use 101.3 J = 1 atm · L.
  • 

Practice Problem: Pressure–Volume Work

• Audio 0:36:20.018920

• To inflate a balloon you must do pressure-volume work on the surroundings. If you inflate a balloon from a volume of 0.100 L to 1.85L, against atmospheric pressure (1.00 atm), how much work is done (in Joules)

Clicker 3

• Audio 0:38:59.416030
• Calculate the change in internal energy (delta E) for a system that is giving off 25.0kJ of heat and is changing from 12.00 L to 6.00 L in volume at 1.50 atm pressure (remember that 101.3 J = 1 L*atm) 25.9 kJ

D

Vocab

Term	Definition
heat capacity	directly proportional to mass
specific heat capacity	the amount of heat energy required to raise the temperature of one gram of a substance 1 °C
molar heat capacity	the amount of heat energy required to raise the temperature of one mole of a substance 1 °C
Pressure volume work	work caused by a volume change against an external pressure (w = –PΔV)