Physical state changes

Physical state changes

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The passages between the three physical states (solid, liquid and gaseous) are called physical state changes.

Look at the following diagram and then read the explanations of each of these changes.

Have you ever seen how on a hot day a piece of ice melts right out of the freezer?

In this case, the solid state water quickly changes to the liquid state. This change of state is known as Fusion.


Heat-induced passage from solid to liquid state.

Heating causes the temperature of the substance to rise to its fusion point. The temperature does not rise while fusion is taking place, that is, only after all the substance has gone into liquid state does the temperature rise again.

O fusion point A substance is the temperature at which the substance changes from solid to liquid.

In the case of water the melting point is 0 ° C. Thus, the ice block will remain at 0 ° C until all of it melts, and then its temperature begins to rise to 1 ° C, 2 ° C, etc.

But the opposite also happens. If we want to pass water from liquid to solid, just put the water in the freezer. This state change is called solidification.


Passage from liquid to solid state through cooling (cooling).
When the liquid substance begins to solidify, the temperature is unchanged until the whole is in solid state, and only then the temperature continues to fall.

In the case of water the solidification point is 0ºC. Thus, the water will remain at 0ºC until all of it freezes for only after its temperature begins to decrease to -1ºC, - 2ºC etc.

Have you ever noticed that when a person is cooking they have to be careful that water does not run out of the pan and food burns and sticks to the bottom? But where does the water go?

Water goes into the gaseous state: it becomes steam, which cannot be seen. The passage from liquid to gaseous state is called vaporization.


Passage from liquid to gaseous state by heating.
If performed slowly it is called evaporation, if it is performed with rapid heating it is called boiling.
During boiling the temperature of the substance from the liquid to the gaseous state remains unchanged, only rising again when the whole substance is in the gaseous state.

O boiling point A substance is the temperature at which that substance changes from liquid to gaseous state.

In the case of water the boiling point is 100 ° C. Thus all water will remain at 100 ° C until all of it has evaporated until only after its temperature begins to rise to 101 ° C, 102 ° C etc.

Water can change from vapor to liquid state. It is easy to observe this passage. How many times have you not put ice water in a glass cup out of the fridge? After a while, the surface outside gets wet, doesn't it?

The small drops of water form because the water vapor in the air comes into contact with the cold surface of the glass and condenses, that is, it goes into a liquid state. This state change is called condensation, or liquefaction.

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Passage from gaseous to liquid state due to cooling (cooling).
When the gaseous substance begins to condense, the temperature remains unchanged until all of it is in a liquid state, and only then does the temperature continue to fall.

An example of condensation is dew and frost!

Sometimes when it is cold, early in the morning we see that many leaves, flowers, cars, windowpanes and other objects that are in the open air are covered with water droplets without raining: It is the dew.

Dew forms when water vapor in the air condenses on contact with surfaces that are colder than air. If the temperature is too low, water may freeze on cold surfaces, forming a layer of ice: it's the frost, which can cause damage to crops as the cold can destroy leaves and fruits.

Have you ever noticed that certain bathroom scent products, for example, shrink in size over time? This is because they move directly from the solid state to the gaseous state. This passage from solid to gas and vice versa is called sublimation.


Direct passage of a substance from the solid state to the gaseous state by heating or from the gaseous state to the solid state by cooling. Eg dry ice, mothballs.