Using the information from the text, write a short summary.
Text 5
Changes in state.
Ordinarily, the temperature of an object. rises when heat flows into it. But under certain circumstances, the addition of heat causes no increase inan object's temperature. Instead, the disorder of the atoms or molecules in the object increases and causes thematerial to change state.
If heat is added to a block of ice that is colder than 0* C, the temperature of the ice will increase until it reaches 0° C, its melting point.Then the temperature will stop increasing for a time, even though more heat flows into the ice. The additional heat will increase the disorder of the molecules in the ice and cause the ice to smelt. But until all the ice has melted, the water will remain at 0° C The heat needed to change ice to water is called the heat of fusion. Each gram of ice at 0° C requires 80 calories of heat to melt it to water at 0° C
As more heat flows into the water at 0° C, the temperature of the water will again rise until it reaches 100° C, its boiling point. Under normal atmospheric pressure, additional heat will not raise the temperature any further. Instead, some of the water will change into steam. Not until all the water has become steam will additional heat cause the temperature to increase again. The heat required to change water at 100° C into steam at the same temperature is called the heat of vaporization. Each gram of water at 100° C requires 540 calories of heat to become steam. More heat added to the steam will raise its temperature above 100° C
A liquid can also become a gas at a temperature below its boiling point through evaporation. Evaporation occurs at the surface of a liquid. The molecules at the surface break free from those below and enter the air as a gas. The speed at which evaporation occurs depends on the kind of liquid, the temperature of the liquid, and the amount of liquid vapor above the liquid.
The heat needed to change a material from a solid to a liquid or from a liquid to a gas is called latent heat. It must be removed to change a gas back to a liquid or a liquid back to a solid. That is, 540 calories of heat must be removed from each gram of steam at 100° C to produce water, and 80 calories must be removed from each gram of water at 0° C to produce ice. The boiling and condensation points of a substance are at the same temperature, as are the melting and freezing points. The amount of heat that has entered or left a substance determines the substance's state.
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Latent heat may also be associated with changes in the structure of the crystals that make up a solid substance. In general, much less latent heat is needed for such changes than for melting or vaporization.
1.Study the following words:
Ordinarily, circumstances, melting point,heat of fusion, the heat of vaporization,.
latent heat, steam, evaporation, be removed, freezing points, solid substance.
2. Complete the sentences with appropriate words from the text:
a) The additional heat will increase the disorder of the ….. in the ice and cause the ice to smelt.
b) ….. occurs at the surface of a liquid.
c) The boiling and condensation …. of a substance are at the same temperature, as are the melting and freezing points.
d) The heat required to change water at 100° C into steam at the same temperature is called the …. …..
e) The heat needed to change ice to water is called the….. …..
3.Insert necessary prepositions:
a) The molecules … the surface break free from those below and enter the air as a gas.
b) The amount … heat that has entered or left a substance determines the substance's state
c) The additional heat will increase the disorder … the molecules … the ice and cause the ice to smelt.
d) In general, much less latent heat is needed … such changes than for melting or vaporization.
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