CHANGES IN STATE OF MATTER 37 



Since the temperature of the ice when it begins 

 melting is C C., and since the temperature of water 

 immediately after melting is 0C., it is evident that 

 the heat has not caused an increase in the temperature 

 of the water. It is thus clear that all the heat must 

 have been used in effecting the change of state from 

 solid ice to water. 



Since the temperature of the water just before it 

 changes into steam is the same as it is after it has all 

 become steam, the heat must be consumed in the change 

 from water to steam. 



Quantity of heat necessary to change ice to water. 

 Heat is necessary to change ice to water. In order to 

 determine the amount of heat necessary for this pur- 

 pose, the experiment must be conducted so that all the 

 heat used will be consumed solely for melting the ice. 



From a number of experiments it has been learned 

 that it requires about 80 calories of heat to change 1 

 gram of ice to water. (See Laboratory Manual, Exercise 

 15.) Heat must then be applied to ice to melt it. 



We have learned that it takes heat to melt ice, or to 

 change it to water. In the laboratory the source of this 

 heat is the Bunsen burner, or some other artificial 

 means. However, when ice melts on exposure to the 

 air, or without any special attempt being made to 

 apply heat to the ice, the fact that a considerable quan- 

 tity of heat is required to melt it is often overlooked. 

 The source of heat in this case is from the air itself 

 and from the surrounding objects. 



