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SPECIFIC HEAT
A THOUGHT EXPERIMENT
Imagine you have two sauce pans, one with 2 liters of water and one with 1 liter of water (at
room temperature). You place them on the stove on identical burners and turn the stove to its highest setting.
Which pan contains the greater mass of water? A
Which pan will require a longer time for the water to reach it’s boiling point? A Which pan will absorb more heat energy for the water to boil? A
When allowed to cool which pan would take longer to reach room temperature? A
Write a statement that describes the relationship between the mass of water and the heat energy transferred to raise its temperature? The greater the mass of water the greater the amount of heat energy needed to raise the temperature of the water.
Now you have two identical sauce pans each with 1 liter of water (at room temperature). You
place them on the stove and turn the burners on high.
Which pan contains water at the greater temperature? B
Which pan will require a longer time for the water to reach its specified temperature? B Which pan will absorb more heat energy for the water to reach its specified temperature? B
When allowed to cool which pan would take longer to reach room temperature? B
Write a statement that describes the relationship between the temperature of water and the heat energy transferred to raise its temperature? The greater the temperature change the greater the amount of heat energy absorbed when heated or released when cooled.
Now you have two identical sauce pans, one with 1 kilogram of water and one with 1 kilogram of
sand (at room temperature). You place them on the stove and turn the burners on high.
Which pan will require a longer time for the contents to reach 100 o^ C? A Which pan will absorb more heat energy for the contents to reach 100 o^ C? A
When allowed to cool which pan would take longer to reach room temperature? A
PART I: HEATING AND COOLING CURVES OF WATER AND SAND
Heating Cooling
Time (min) 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Water Temp ( oC)
Sand Temp. ( oC)
Time (min) 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 Water Temp ( oC)
Sand Temp. ( oC)
What was the temperature change for each substance while heating?
Sand (99 – 23 = 76 degrees) Water (59 – 23 = 36 degrees)
How long did it take each substance to reach its highest temperature?
Sand 7 minutes Water 7 minutes
Which substance increased temperature the fastest? Sand
What was the temperature change for each substance while heating?
Sand (99 – 54 = 45 degrees) Water (59 – 37 = 22 degrees)
Which substance cooled the fastest? Sand
Is the amount of thermal energy absorbed by each substance equal, or did one substance
absorb a greater amount of thermal energy than the other? Explain your reasoning.
Since the sand and the water were on the hot plate the same amount of time, both substances absorbed the same amount of thermal energy.
As you have seen, the addition of heat to a substance results in an increase in its temperature. The
amount of this increase depends on the ability (capacity) of the substance to retain this heat. The tendency of a substance to resist a change in temperature after absorbing or releasing some heat is the specific heat capacity of the substance. This quantity is analogous to inertia (object resists a change in motion).
Which substance has a greater resistance to a change in temperature? Water
Which substance has a greater specific heat capacity? Water
Match the substance with the two specific heat capacities
4180 j / kg o^ C Water 664 j / kg o^ C Sand
PART II: INVESTIGATING SPECIFIC HEAT CAPACITIES OF METALS
Sample: Aluminum Mass: 68.65 g or 0.06865 kg massmetal
- Temperature of metal in boiling water: 100.0 degrees metalinitial
- Mass of water in Styrofoam cup: 200.0 g or 0.200 kg masswater
- Temperature of water in cup: 23.0 degrees waterinitial
- Temperature of water and metal: 27.8 degrees waterfinal 27.8 degrees metalfinal
- Determine the changes in temperature for the water and the metal.
UT metal (100.0 degrees – 27.8 degrees = 72.2 degrees)
UT water (27.8 degrees – 23.0 degrees = 4.8 degrees)
- Here is another variation using specific heats. Suppose a steel bolt, with a mass of 95.00 g (specific heat = 450 j/kg o^ C) is heated to red-hot in a flame. It is added to a container of water with 100.0 mL of water at 25 o^ C to cool off. The water in the cup rises to 80 o^ C. What was the temperature of the bolt before it was added to the cup?
Hint: Fill out the values you know. Put a question mark on the value you’ll be solving for.
Water
Mass: 0.1000 kg Specific heat: 4190.0 j/kg o^ C Final Temp: 80.0 o^ C Inititial Temp: 25.0 o^ C
Steel
Mass: 0.09500 kg Specific heat: 450.0 j/kg o^ C Final Temp: 80.0 o^ C Initial Temp: ??
Show your calculation below to determine the initial temperature of the bolt.
massmetal x specific heatmetal x UTmetal = masswater x specific heatwater x UTwater
(0.09500 kg) x (450 j/kg o^ C) x (T (^) initial – 80 o^ C) = (0.1000 kg) x (4190 j/kg o^ C) x (55 o^ C)
Algebraically rearrange and solve for Tinitial :
619 o^ C
