Thermal Properties of Matter

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Thermal Properties of Matter

• Specific Heat Capacity

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• Level
• Secondary 3 Express (Pure Physics)
• Duration
• 2 periods (70 minutes)
• Venue
• Physics Laboratory

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Lesson Objectives

• Define the terms heat capacity and specific heat
  capacity.
• Deduce the formula for heat capacity and specific
  heat capacity
• Apply the above formulas to solve related
  problems.
• Apply the knowledge of the high heat capacity of
  water to everyday applications.

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Introduction
Balloon filled with Air and Water
Balloon filled with Air
Candle
A
B
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Question

• If balloons A and B are heated by the candle,
  which one will burst?
• Both balloon A and B will burst
• Balloon A only
• Balloon B only
• None of them will burst
• Support your answer with a reason.
• Result Only Balloon A will burst. Why?

Stay tuned to find out!
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Recall

• Touch a metal spoon and a plastic spoon. Do you
  feel a difference?
• Are they at the same temperature?
• Good heat conductors conduct heat away from our
  skin more easily, making us feel cold.
• Application Frying pan

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Expt 1A Heating 20 ml water

• Refer to calorimetry.html
• Heat 20 ml of water, power 100W for 10 sec.
• Note the initial and final temperature.

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Expt 1B Heating 40 ml water

• Heat 40 ml of water, power 100W for 10 sec.
• Note the initial and final temperature.

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Heat capacity

• For the same amount of heat energy supplied,
  different amounts of water have a different rise
  in temperature.
• More water ? rise in temperature is lower ? need
  to supply more heat to achieve the same rise in
  temperature ? higher heat capacity

Heat Capacity
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Experiment 2

• For the same amount of different substances, will
  they have different heat capacities?
• Refer to Experiment 2 in worksheet

VS
Water
Cooking Oil
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Formal Definition

• The same amount of heat supplied to different
  amounts of the same substance (water in this
  case) cause different rise in temperature.
  Likewise for same amounts of different
  substances.
• How do we measure how much heat will raise the
  temperature by how much?

Heat Capacity The amount of heat energy needed
to raise the temperature of a substance by 1
degree Celsius or 1 Kelvin
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Formula of Heat Capacity

• From definition
• Unit J/K or J/oC
• More useful form
• We write as

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Exercises

• When a piece of iron is heated from 30?C to 60
  ?C, the heat absorbed is 6000J. Calculate its
  heat capacity
• A piece of copper has a heat capacity of 30 J/K.
  What is the amount of heat given out when it is
  cooled from 290 K to 200 K.
• For experiments 1A and 1B, given that the heat
  capacity of the calorimeter is 53.64 J/K,
  calculate the respective heat capacity of water
  in both experiments.

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Specific Heat Capacity

• As observed from Expt 1A and 1B, since the heat
  capacity of water is dependent on the amount of
  water, it is more meaningful to look at heat
  capacity per unit mass of a substance.
• The heat capacity of 1 g of the same substance
  (in this case water) is always the
• same. This is called its specific heat capacity.

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Specific Heat Capacity

• Specific Heat Capacity The amount of heat
  energy needed to raise the temperature of 1 kg of
  substance by 1 degree Celsius or 1 Kelvin

• From definition
• Unit J/K or J/oC

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Specific Heat Capacity

• More useful form
• Heat Supplied Mass Specific Heat Capacity
• Change in Temperature
• We write as

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Exercises

• Based on your observations in Experiment 2, what
  can we say about the specific heat capacities of
  water and oil? Explain why we use oil in cooking
  with regards to its specific heat capacity.
• A piece of iron of mass 5 kg has a heat capacity
  of 2220 J K-1. Find its specific heat capacity.
• Find the amount of heat energy needed to raise
  the temperature of 500g of water from 0oC to
  100oC. Take the specific heat capacity of water
  to be 4186 J/kgoC.

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Exercises

• What are the applications that make use of the
  high specific heat capacity of water?
• What are the differences between heat capacity
  and specific heat capacity of a substance?

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Applications

• Hot water bottle to keep warm on cold nights.
• Water used as cooling liquid in car engines
• Land and Sea breezes.
• Others?

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So

• The balloon is stretched very thin by air and
  water.
• Due to the high heat capacity of water, heat from
  the candle is quickly absorbed by the water and
  the temperature does not rise high enough to melt
  the balloon.

Balloon filled with Air and Water
B
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Japanese Paper Steamboat
Paper Container
Boiling Soup
Fire
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Insulators vs Conductors

• Heat insulators have a high heat capacity so that
  they do not get hot easily.
• Conversely, heat conductors generally have low
  heat capacity (eg copper has specific heat
  capacity of 385 J/kgK.

Heat insulator
Heat conductor
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Summary

• Definitions of Heat capacity and Specific Heat
  Capacity

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• Reminder Practice the questions at the end of
  the worksheet as homework before the next lesson.
• The End