Heat as energy
Heat is energy transferred from one object to
another because of a difference in
temperature
Heat naturally flows from high temperature to
low temperature.
Heat
• Joule determined that a certain amount of
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mechanical work resulted from a specific amount
of heat input. Joule is credited with defining
Heat as energy (or transfer of energy)
Heat is measure in calories or Joules.
1cal = 4.186J
1 cal is the amount of heat necessary to raise
the temperature of 1 gram of water by 1 degree
C.
Heat
• 14-3 Specific Heat
– When you heat an object, the temperature rise
depends on mass of the object and a property of the
material called “specific heat”.
– Q = mc(T2-T1)
– Q = amount of heat, m = mass, c = specific heat, T
= temp.
– The higher the heat capacitance, the smaller the
temp change for a given amount of heat input.
Heat
• Calorimetry – solving problems
• In a closed system, the heat is transferred
from the hot object to the cold object or
heat lost by one object = heat gained by
another.
Heat
• Latent Heat
– When a material changes phases from a solid to liquid or from
liquid to gas, a certain amount of energy is involved in the phase
change. This is called the latent heat.
– Heat of Fusion: heat required to change from a solid to a liquid.
– Heat of Vaporization: heat required when changing from liquid to
gas.
– Q = mL where m = mass and L = latent heat (look this up in a
table)
– During a phase change, the material’s temperature stays
constant.
Heat
• Solving Calorimetry problems
• Apply conservation of energy
– Heat gained = heat lost
• If no phase changes occur, each term will have the form
Q(gain) = mc(Tf-Ti) or Q(lost) = mc(Ti-Tf)
• If phase changes occur, must account for these Q = mL
• When the system reaches equilibrium, the final
temperature of each substance will have the same value.