YEAR 11 PHYSICS Heat Revision
Specific heat capacity of air = 1.01 x 10 ³ J kg
-1
Specific heat capacity of aluminium = 900 J kg
K
-1
-1
Specific heat capacity of water = 4180 J kg
-1
K
-1
K
-1
Specific heat capacity of copper = 385 J kg
-1
K
-1
Specific heat capacity of solid lead = 128 J kg
-1
K
-1
Latent heat of fusion of lead = 2.3 x 10
4
J kg
-1
1.
Draw a labelled heating curve for an unknown mass of ethanol that is heated from a solid to a gas.
Ehanlol’s melting point is -115 o
C and its boiling point is 78 o
C .
78
-114
4 marks
2.
Circle the regions of the heating curve where the kinetic energy of the ethanol molecules is increasing.
Explain why we know the kinetic energy of the ethanol molecules is changing during the periods you circled.
These regions are increasing in temperature which is caused by particles moving more rapidly, which is an increase in kinetic energy.
2 marks
3.
When the ethanol boils the potential energy of its molecules changes. Does it increase or decrease during boiling? Explain why the potential energy of the ethanol molecules changes when it boils. a.
Increase or decrease: _increase__ b.
Explanation:
When particles separate and increase the distance between them (such as in boiling), there is an increase in potential energy
2 marks
4.
How much heat is lost from a 5.0 kg block of copper when it cools from 305 o
C to 170 o
C?
2 marks
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5.
A 200 g glass beaker containing 300 g of water requires 6.94 x 10
4
J of energy in order to change the temperature from 30.0
o
C to 80.0
o
C. Calculate the specific heat of the glass.
3 marks
6. A large 3.50 x 10
3
W kettle uses 1.946 x 10
6
J to completely boil away the contents of a kettle. Calculate the time (in minutes) that it would take for this to occur.
3 marks
7. 2. A 500 g block of aluminium metal is initially heated to 80 C and then placed into 650 g of cold water at 15.0 C. Assuming that no heat is lost to the surroundings, determine the final temperature of the aluminium and water.
2 marks
8. What mass of water can be raised in temperature from 15.0
0
C to its boiling point when 4.95 x 10
4
J of heat is supplied? the alloy from 15.0
0
C to 92.5
2 marks
9. What is the specific heat of an alloy if it requires 3.20 x 10
4
J of energy to heat 1.20 kg of
0
C?
2 marks
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10. A hot water bottle contains 4.5 kg of water at 50.0
0
C. At what rate is water losing heat if it cools to 38.0
0
C over 6 hours?
3 marks
11. 1.5 kg of molten lead, at its melting point is poured into a large tub of water. The lead is initially at a temperature of 327
0
C while the 10 L of water was at 27
0
C. The melting point of lead is 327
0
C. What is the final temperature of the mixture?
4 marks
Comprehension:
The study of heat processes is called thermodynamics. The processes studied include the effects of heat on various states of matter, and the ways in which heat is related to other forms of energy. All heat processes conform to the fundamental laws of thermodynamics.
The First Law of Thermodynamics states that energy is neither created nor destroyed in the conversion of heat to or from other forms of energy. The Second Law of Thermodynamics states that a transfer of heat from one body to another proceeds naturally and continuously from the warmer to the cooler body.
Heat energy is most intense in substances whose molecules are moving rapidly in a very disorderly way.
Such a substance will give up some of its heat to another substance whose molecules are less agitated.
When this happens, the heat is said to “flow” from one substance to another (or from one body to another). The energy transfer is indicated by a change in temperature.
Temperature, therefore, is not the same thing as heat—although the two words are often used interchangeably. Temperature can be defined as the degree of intensity of hotness or coldness. “Hotness” and “coldness,” however, are comparative terms. A flame, for example, is hot when compared with ice but cold when compared with the sun. This definition of temperature, therefore, is vague and unscientific, although it does convey the correct impression that temperature is a measure of relative intensity rather than of quantity.
A more specific definition is: temperature is the ability of one body to give up heat energy to another body. A hot body becomes cooler, and a cold body becomes warmer, as long as heat is flowing from one to the other. The hot body has a greater ability to give up heat and therefore has a higher temperature.
After a time the two bodies may reach a condition of heat equilibrium, or balance of heat intensity. Then, heat flow ceases. At the point of equilibrium both bodies can be said to be at the same temperature.
Experiments have shown that every 1° C. increase or decrease in temperature causes the pressure exerted by a gas to increase or decrease at the constant rate of 1/273.15 of its pressure at 0° C. This means that at
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-273.15° C. an ideal (theoretical) gas would exert no pressure at all. Since experiments with real gases have shown a clear relation between pressure and temperature, zero pressure would indicate that the ideal gas had lost all its ability to give up heat. Its molecules would be absolutely motionless. This is impossible—molecules are always agitated, to some extent—and therefore the absolute zero of temperature remains a theoretical concept. The concept is, however, a useful one, for it gives a base point to which all temperature measurements may be referred, in positive numbers.
The idea that absolute zero can never be reached is sometimes considered important enough to be called the third law of thermodynamics. Scientists have succeeded in cooling substances to within a small fraction of a degree above absolute zero. The study of the behavior of substances at very low temperatures is called cryogenics. Absolute zero is the lower limit for temperature, but there is no upper limit. The hottest substances known are ionized gases in certain stars, with temperatures of a billion degrees or more.
12.
Describe the difference between heat and temperature?
Heat is an energy which is determined by the movement of particles in a substance while temperature is a measure of the intensity of hotness.
2 marks
13.
Determine the pressure of a gas at -80
0
C be if its pressure was 180 kpa at 0
0
C?
2 marks
14.
Describe why reaching absolute zero a theoretical impossibility?
Absolute zero requires zero pressure and no movement of particles. In reality all particles are moving, if only a little bit which makes it impossible to reach absolute zero.
2 marks
15.
Explain why there is there no such thing as an upper limit of temperature.
Increasing temperature means increasing the kinetic energy of the particles. Since particles can always be made to move faster, there is no limit the how high temperature can go.
2 marks
Heating and Cooling Revision Developed by Mr D. Patterson