6.3 Heat Capacity
If you were to heat up a pot of water
on your stove top it would take a
considerable amount of time. However,
if you were to heat up the same
amount of vegetable oil, under the
same conditions, the oil would heat up
more quickly.
Conversely, if both pots were left to
cool down, the vegetable oil would cool
much faster than the water.
Why do different substances warm up
and cool down at different rates?
6.3 Specific Heat Capacity
specific heat capacity (c) is the amount of
energy required to increase the temperature of
1 kg of a substance by 1 °C.
SI units ⤍ J/(kg⋅°C); joules per kilogram-Celsius
It takes 4.18 x 103 J of energy to raise the
temperature of 1 kg of water by 1°C.
Vegetable oil, on the other hand, only requires
2.0 x 103 J of energy; less than half as much.
Oil and water are composed of different types
of molecules that require different amounts of
energy to increase their own kinetic energies.
6.3 Quantity of Heat
The total amount of thermal energy transferred from a warmer substance to a
colder substance is called the quantity of heat (Q).
Mathematically, the quantity of heat (Q) is directly proportional to the mass (m) of
the substance, its specific heat capacity (c), and the change in temperature (∆T)
the substance undergoes.
SI units: Q ⤍ J; m ⤍ kg; c ⤍ J/(kg⋅°C); ∆T ⤍ °C , where ∆T = T2 – T1
If a substance absorbs thermal energy ⤍ ∆T is positive.
If a substance releases thermal energy ⤍ ∆T is negative.
SP #1-3 p.282-283
6.3 Principle of Thermal Energy Exchange
The principle of thermal energy exchange states that when thermal energy is
transferred from a warmer object to a colder object, the amount of thermal energy
released by the warmer object is equal to the amount of thermal energy absorbed
by the colder object.
In other words, when a warmer object comes into contact with a colder object,
thermal energy is transferred until it is evenly distributed in both objects; both
objects will have the same final temperature.
SP #1,2 p.284-285
6.3 Thermal Expansion & Contraction
As a substance absorbs thermal energy, its
particles increase in kinetic energy and
spread out; increase in volume. The increase
in volume due to an increase in temperature
is called thermal expansion.
Likewise, when a substance cools down, its
particles release kinetic energy and decrease
in volume, resulting in thermal contraction.
Civil engineers make use of expansion joints in
bridges and spaces between slabs of concrete
on sidewalks to help to prevent against damage
on hot summer days.
6.3 Homework
Practice # 2,3 p.283
Practice # 1 p.286
Questions # 1, 3, 5, 7, 9 p.287