Physical properties are properties that can be measured about a substance without changing the substance. For example, mass, volume, density, boiling point, and freezing point are all physical properties of matter. One other very important physical property of matter is state of matter. The three states of matter are solid, liquid, and gas. (For all you scientists out there thinking…”What about plasma?”, we’ll save that for another time.)
In elementary school, you probably remember reading about the states of matter. The states of matter (solid, liquid, and gas) are also called the phases of matter. Therefore, when matter changes from a solid to a liquid or from a liquid to a gas, there has been a change in the phase. Hence, a phase change has taken place. Examples of phase changes include melting, freezing, condensation, evaporation, sublimation, and deposition.
One very important aspect of phase changes is the shift in energy that occurs during a reaction. In some reactions, energy may be needed in order for it to take place. In other cases, energy may be released when the change has occurred. If heat is given out or released in a phase change it is an exothermic
reaction. After these reactions take place, you are able to feel the surroundings get hot. Freezing and condensing are exothermic. The majority of reactions are exothermic reactions. If heat is taken in or absorbed from its surroundings, it is an endothermic reaction. In these reactions, you are able to feel the surroundings feel cold. Melting, evaporating, and sublimation are endothermic reactions.
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Draw the molecules of a
Draw the molecules of a liquid before evaporation. gas after evaporation.
On the lines below the boxes, describe the molecular motion AND arrangement in a few words.
Molecules of water are always trying to escape from the liquid state into the vapor state.
That is why a glass of water will evaporate if left uncovered.
If the molecules are moving faster after evaporation (when they are in a gaseous state), that means that they needed to ____________ energy before the change took place. If energy is taken in, this makes evaporation an ___________________ reaction.
Doesn’t it make sense? When we sweat, water is evaporated from our skin and turned into water vapor. In order to do this, the reaction takes energy from our skin to give it the energy to escape. Because our skin loses this energy, it feels cool! This is why we sweat!
Evaporation is an endothermic reaction that causes its surroundings to cool!

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Draw the molecules of a solid before melting.
Draw the molecules of a liquid after melting.
On the lines below the boxes, describe the molecular motion AND arrangement in a few words.
If the molecules are moving faster after melting (when they are in a liquid state), that means that they needed to _________________ energy before the change took place.
If energy is taken in, this makes melting an ___________________ reaction.
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Draw the molecules of a
Draw the molecules of a liquid before boiling. gas after boiling.
On the lines below the boxes, describe the molecular motion AND arrangement in a few words.
Molecules of water are always trying to escape from the liquid state into the vapor state.
This is why a glass of water will evaporate if left uncovered. When water boils, many water molecules are escaping quickly. The pressure of the air above prevents water molecules from escaping more quickly. As water is heated, the water molecules gain enough energy to break free from the liquid and escape as a vapor.
If the molecules are moving faster after boiling (when they are in a gaseous state), that means that they needed to _________________ energy before the change took place.
If energy is taken in, this makes boiling an ___________________ reaction.

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Draw the molecules of a solid before sublimation.
Draw the molecules of a gas after sublimation.
On the lines below the boxes, describe the molecular motion AND arrangement in a few words.
If the molecules are moving faster after sublimation (when they are in a gaseous state), that means that they needed to _________________ energy before the change took place. If energy is taken in, this makes sublimation an ___________________ reaction.
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Draw the molecules of a
Draw the molecules of a gas before condensation. liquid after condensation.
On the lines below the boxes, describe the molecular motion AND arrangement in a few words.
If the molecules are moving slower after condensation (when they are in a liquid state), that means that they needed to _________________ energy before the change took place. If energy is released, this makes condensation an ___________________ reaction.

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Draw the molecules of a liquid before freezing.
Draw the molecules of a solid after freezing.
On the lines below the boxes, describe the molecular motion AND arrangement in a few words.
If the molecules are moving slower after freezing (when they are in a solid state), that means that they needed to _________________ energy before the change took place.
If energy is released, this makes freezing an ___________________ reaction.
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Draw the Draw the molecules of a gas before molecules of a solid after deposition. deposition.
On the lines below the boxes, describe the molecular motion AND arrangement in a few words.
If the molecules are moving slower after deposition (when they are in a solid state), that means that they needed to _________________ energy before the change took place.
If energy is released, this makes deposition an ___________________ reaction.