PHYS1006 Lecture Notes - Lecture 15: Iceberg, Calorimetry, Latent Heat

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25 Jun 2018

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Specific Heat

Heat and Energy

Heat is the energy that flows from a hot object to a colder object.

Specific Heat

The amount of heat required to change the temperature of a material is proportional to the

mass and to the temperature change.

Where m is mass, c is the specific heat, T is time and Q is the amount of heat required to

change the temperature of a material.

It is defined as the heat needed to increase the temperature of 1kg of a

substance by 1oC or 1 Kelvin degree.

Example 1

Pour 3.0kg of water at 20.0 oC into a steel pan of mass 0.90kg and put it on a stove to boil.

After some time, the steel pan and water will reach a temperature of 100.0oC.

Which of the following is true?

a) The pot requires more heat energy.

b) The water requires more heat energy.

c) They both require the same amount of heat energy.

ANSWER: B

Example 2

How much heat energy is required by the water and steel pan to reach 100.0oC?

Heat required by water:

The mass of the water is 3.0kg

The specific heat of the water is 4186

The change in temperature is 20oC to 100oC.

Heat required by pan:

The mass of the pan is 0.90kg

The specific heat of iron/steel is 450

The change in temperature is 20oC to 100oC.

Therefore, water requires about 31 times more heat energy to reach 100oC.

Example 3

How long will a 2400W electric kettle take to boil 2.0kg of water at a temperature of 20.0oC?

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Document Summary

Heat is the energy that flows from a hot object to a colder object. The amount of heat required to change the temperature of a material is proportional to the mass and to the temperature change. Where m is mass, c is the specific heat, t is time and q is the amount of heat required to change the temperature of a material. It is defined as the heat needed to increase the temperature of 1kg of a substance by 1oc or 1 kelvin degree. Pour 3. 0kg of water at 20. 0 oc into a steel pan of mass 0. 90kg and put it on a stove to boil. After some time, the steel pan and water will reach a temperature of 100. 0oc. Which of the following is true: the pot requires more heat energy, the water requires more heat energy, they both require the same amount of heat energy. Therefore, water requires about 31 times more heat energy to reach 100oc.

Related Questions

120 grams of boiling water (temperature 100Â° C, heat capacity 4.2J/gram/K) are poured into an aluminum pan whose mass is 1100 gramsand initial temperature 22Â° C (the heat capacity of aluminum is 0.9J/gram/K).

(a) After a short time, what is the temperature of the water?
Tfinal = C

(b) What simplifying assumptions did you have to make?

-Energy transfer between the system (water plus pan) and thesurroundings was negligible during this time.
-The heat capacities for both water and aluminum hardly change withtemperature in this temperature range.
-The thermal energy of the aluminum doesn't change.
-The thermal energy of the water doesn't change.

(c) Next you place the pan on a hot electric stove. While the stoveis heating the pan, you use a beater to stir the water, doing 26432J of work, and the temperature of the water and pan increases to77.8Â° C. How much energy transfer due to a temperature differencewas there from the stove into the system consisting of the waterplus the pan?
Q = J

120 grams of boiling water (temperature 100Â° C, heat capacity 4.2J/gram/K) are poured into an aluminum pan whose mass is 1100 gramsand initial temperature 22Â° C (the heat capacity of aluminum is 0.9J/gram/K).

(a) After a short time, what is the temperature of the water?
Tfinal = C

(b) What simplifying assumptions did you have to make?
-Energy transfer between the system (water plus pan) and thesurroundings was negligible during this time.
-The heat capacities for both water and aluminum hardly change withtemperature in this temperature range.
-The thermal energy of the aluminum doesn't change.
-The thermal energy of the water doesn't change.

(c) Next you place the pan on a hot electric stove. While the stoveis heating the pan, you use a beater to stir the water, doing 26432J of work, and the temperature of the water and pan increases to77.8Â° C. How much energy transfer due to a temperature differencewas there from the stove into the system consisting of the waterplus the pan?
Q = J

The heat capacity, C, of an object is defined as the amount ofheat needed to raise its temperature by 1 CÂ°. Thus, to raise thetemperature by ÎT requires heat Q given by the followingequation.

Q = CÎT

(a) Write an expression for the heat capacity C of the material.(Use c for the specific heat and m for the mass.)

(b) What is the heat capacity of 1 kg of water?

J/CÂ°

(c) What is the heat capacity of 54 kg of water?

J/CÂ°

PHYS1006 Lecture Notes - Lecture 15: Iceberg, Calorimetry, Latent Heat

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