Specific Heat
SPH3U
Ms. Kueh
Thermal Conductor - a material that is a good conductor of thermal energy
Example -
Thermal Insulator - a material that is a poor conductor of thermal energy
Examples - plastics, fur, fibreglass, foam insulation
-some insulators trap air and help to prevent the transfer of thermal energy from an
object to its surroundings.
-Gases (like air), have a lot of space between particles, so kinetic energy is not
passed very quickly between particles in a gas.
How does a thermos work? See the image to the right.
Heat Capacity
If you heated up a pot of water and a pot of oil on a stove, which would heat
up faster?
If you left the two on the stove and waited for them to cool down, which would cool down faster?
It actually takes more energy to increase the temperature of 1.0 𝑘𝑔 of
_______________________________ by 1°𝐶 than it takes to increase the temperature of 1.0 𝑘𝑔 of
_______________________________ by 1°𝐶.
_____________________________________ - the amount of energy needed to raise the temperature
of a 1 𝑘𝑔 substance by 1°𝐶
To raise 1.0 𝑘𝑔 of water by 1°𝐶, would take about 4.18 × 103 𝐽 of energy. We say that the specific heat
capacity of water is 4.18 × 103 𝐽/(𝑘𝑔°𝐶)
or
4.18 × 103 𝐽/(𝑘𝑔𝐾).
The specific heat capacity of oil is 2.0 × 103 𝐽/(𝑘𝑔°𝐶) which means it takes
about half as much energy to heat oil as it does water. This means that a
1 𝑘𝑔 pot of water at 10°𝐶 takes twice as much energy to reach 100°𝐶 as a
1 𝑘𝑔 pot of oil at 10°𝐶.
Quantity of Heat (Q) - The total amount of thermal energy transferred from
a warmer substance to a colder substance
-
Depends on the mass (𝑚) of the substance, the specific heat
capacity (𝑐)and the change in the temperature (∆𝑇)
-
If an object is heated (temperature _______________ ), it
absorbs energy, therefore change in energy is _______________
-
If an object cools (temperature ___________________), it loses
energy, therefore change in energy is _________________
𝑄 = 𝑚𝑐∆𝑇
Example 1
A block of wood, mass 2.5 𝑘𝑔, is heated from −10°𝐶 to 35°𝐶. If the specific heat
capacity of wood is 1.8 × 103 𝐽/(𝑘𝑔𝐾) how much thermal energy did it gain?
Example 2
When 200.0 𝑚𝐿 of water is heated from 15.0°𝐶 to 40.0°𝐶, how much thermal energy is
absorbed by the water? Remember:
1 𝑚𝐿 = 1 𝑐𝑚3
and
1 𝑐𝑚3 = 1 𝑔
Example 3
An empty copper pot is sitting on a burner. The pot has a mass of 1.2 𝑘𝑔 and is at a
temperature of 130.0°𝐶. If the pot cools to a room temperature of 21.0°𝐶, how much
thermal energy does it release to the surroundings?
Example 4
A 0.454 𝑘𝑔 block of lead starts at 65°𝐶. It then releases 4560 𝐽 of thermal energy to
the surrounding air. What is the new temperature of the lead?
Example 5
A 50.0 𝑘𝑔 sample of some metal takes 9.0 × 105 𝐽 of thermal energy to raise its
temperature from 300 𝐾 to 375 𝐾. What type of metal is it?
The Principle of Thermal Energy Exchange - 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.
𝑄𝑟𝑒𝑙𝑒𝑎𝑠𝑒𝑑 + 𝑄𝑎𝑏𝑠𝑜𝑟𝑏𝑒𝑑 = 0
Example 6
A 60.0 𝑔 sample of metal is heated to 100.0°𝐶 before being placed in 200.0 𝑚𝐿 of
water with an initial temperature of 10.0°𝐶. The metal-water combination reaches a
final temperature of 15.6°𝐶. Determine the identity of the metal.
Example 7
200.0 𝑔 of silver is heated to 90.0°𝐶. The hot silver is then placed into 300.0 𝑔 of ethyl
alcohol that has an initial temperature of 5.0°𝐶. Determine the final temperature of the
silver-alcohol mixture.
Example 8
An electric kettle is used to heat up 1.5 𝑘𝑔 of water for tea from 8.0°𝐶 to 100°𝐶.
(a) How much energy did it take?
(b) The kettle has a power of 2000 𝑊. Assuming 100% efficiency, how long did it
take?
Homework: pg. 262 #1 – 3
pg. 275 #5, 8, 24 – 27, 6, 30-33
Answers: