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exothermic change, the system releases energy to its surroundings. Freezing is an example of an exothermic change. Charactaristics of Phase Changes ...
Typology: Exercises
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A large iceberg contains enough fresh water to supply millions of people with water for a year. As it moves into warmer areas, the ice changes to liquid water and eventually disappears. What happens when a substance changes from one phase to another?
Melting, freezing, vaporization, condensation, sublimation, and deposition are six common phase changes.
When at least two states of the same substance are present, scientists describe each different state as a phase. A phase change is the reversible physical change that occurs when a substance changes from one state of matter to another.
Charactaristics of Phase Changes
The temperature of a substance does not change during a phase change.
One way to recognize a phase change is by measuring the temperature of a substance as it is heated or cooled.
Charactaristics of Phase Changes
Temperature and Phase Changes
This is a graph of the data collected when a solid piece of naphthalene is slowly heated. The temperature of the naphthalene rises until it reaches 80°C. The temperature remains at 80°C, the melting point of naphthalene, until melting is complete.
Charactaristics of Phase Changes
Energy is either absorbed or released during a phase change.
During a phase change, energy is transferred between a substance and its surroundings. The direction of the transfer depends on the type of phase change.
Charactaristics of Phase Changes
Energy and Phase Changes
This ice sculpture of a dog sled was carved at a winter fair in Fairbanks, Alaska. The ice sculpture will start to melt if the temperature rises above 0°C or sunlight shines directly on the ice.
Charactaristics of Phase Changes
Energy released as ice forms on these strawberry plants keeps the plants from freezing at temperatures slightly below 0°C
Charactaristics of Phase Changes
One gram of water releases 334 joules of energy to its surroundings as it freezes, the same amount of energy that is absorbed when one gram of ice melts. As water freezes, it releases heat. The flow of heat slows the drop in temperature and helps protect the crops from damage. During an exothermic change, the system releases energy to its surroundings. Freezing is an example of an exothermic change.
Charactaristics of Phase Changes
Melting Each water molecule contains two hydrogen atoms and one oxygen atom. In ice, attractions between water molecules keep the molecules in fixed positions. Any energy gained by the water after a phase change increases the average kinetic energy of the molecules, and the temperature rises.
Melting and Freezing
When ice cubes are removed from a freezer, heat flows from the air to the ice.
Melting and Freezing
When liquid water is placed in a freezer, energy flows from the water to the air in the freezer, and the water cools.
Melting and Freezing
The phase change in which a substance changes from a liquid into a gas is vaporization.
Vaporization and Condensation
In a refrigerator, a pair of phase changes keeps the food cold.
Vaporization and Condensation
Evaporator
Compressor
Condenser
Energy released to surroundings
Energy removed from food compartment
Evaporation After a rain shower on a sunny, warm day, you may notice puddles of water. After a few hours, the puddles may be gone due to evaporation. Evaporation changes a substance from a liquid to a gas at temperatures below the substance’s boiling point.
Vaporization and Condensation
