States of Matter and Phase Changes

Matter can be found as solids, liquids, gasses, plasmas, and even Bose-Einstein condensates. What makes each of the phases of matter different is how the molecules react to their kinetic energy and the strength of the molecular bonds. As kinetic energy (measured as temperature) goes up, the ability of the bonds to hold the molecules together is less and less, and eventually, the matter will change state—solids melt into liquids, liquids vaporize into gases, and gases ionize into plasmas. If kinetic energy goes down, the reverse happens.

phase of matter

A distinct form of any type of matter related to its molecular properties commonly including: solids, liquid, gas, or plasma. At any given temperature, any specific matter will be found in a particular phase.

A phase change is when… matter changes from one phase to another. This occurs at specific temperature for each substance. 

When a substance reaches a phase change point (such as freezing/melting point or boiling point), instead of raising the temperature, the added energy causes the molecules to rearrange. Solids will lose their definite shape and liquids will lose their definite volume because the energy does not raise the temperature, but rather overcomes the attractive forces that hold the substance together.

Each phase change has a specific name.

Eight Phase Changes + 1 More

As kinetic energy increases, matter will change from one phase to another. Likewise, as energy decreases, matter will also change phase. Each phase change has a particular name.

Melting: the process of changing from solid to liquid.

Freezing: the process of changing from liquid to solid.

Vaporization: the process of changing from liquid to gas at its boiling point.

Condensation: the process of changing from gas to liquid.

Sublimation: the process of changing from solid to gas.

Deposition: the process of changing from gas to solid.

Ionization: the process of changing from a gas to a plasma.

Recombination/deionization: the process of changing from plasma to gas.

For most substances, the changes in phase will happen at specific temperatures. These temperatures are known as the freezing/melting point and boiling point.

It is possible, however, for liquids to become gases, even though the liquid never reaches the boiling point. Water spilled on a table will eventually dry up, even though the air never reaches 100C around it. This is due to a process called evaporation.

Evaporation is the process that changes a substance from a liquid to a gas at temperatures below the substance's boiling point.

https://youtu.be/ZOjdzYEgbSQ

During a phase change, the temperature of a substance will not change. Rather the energy being transferred breaks or forms the molecular bonds. Only after (for example in the case of melting) all of the molecules of the solid have broken free and become liquid will the temperature begin to go up. For any substance, there is a specific amount of energy needed to break the bonds that hold the molecules in a particular shape or volume.

The amount of energy given off when a liquid becomes a solid (or taken in when a solid becomes a liquid) is called the heat of fusion.

The amount of energy given off when a gas becomes a liquid (or taken in when a liquid becomes a gas) is called the heat of vaporization.

Two Types of Phase Changes

Energy is either absorbed or released in a phase change. For example, for a solid to become a liquid, the energy that is absorbed results in the bonds holding the solid together to break. To reverse it, the liquid molecules must give up energy in order for the molecular bonds to "grab" them and force them into the rigid shape of a solid.

There are two different names for the type of phase change depending on if energy is absorbed or given off.:

Endothermic changes (or reactions) take energy IN. The process absorbs energy from it surroundings. Another way to think of this is that energy ENters the system.

Exothermic changes (or reactions) give off energy—energy EXits from the system. The process releases energy into its surroundings.

The following phase changes are Endothermic (require energy to be added to the molecules to cause them to change state):

• Melting
• Vaporization
• Sublimation
• Ionization

The following phase changes are Exothermic (the molecules give up energy in order to "settle" into the new state):

• Freezing
• Condensation
• Deposition
• Recombination/deionization

Amorphous Substances

Not all matter has a fixed melting point. Think about butter. It softens gradually from being hard in the refrigerator as it reaches room temperature.

Matter that does not have a fixed, set melting point is amorphous. 

Kinetic theory still applies, however. As the kinetic energy of the molecules increase, the bonds that hold the substance in shape and to a fixed volume are "stretched" and become lax. This allows the orientation between the molecules to become variable and easily adjusted. Hence, the substance becomes softer and will somewhat change shape, though not actually a liquid.

There are many examples of amorphous matter including glass and asphalt. 

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Another look at this material: https://youtu.be/Mfuud7WRfNA

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Definitions and content from:

New Oxford American Dictionary

Physical Science Concepts in Action, Pearson

http://en.wikipedia.org

Physical Properties of Matter

Intro to Physics and Chemistry Index

General Chemistry Index

Physical Properties of Matter

A physical property is any attribute, quality, or characteristic of a material that can be observed or measured without changing the composition of the substances in the material. There are many different properties that can be observed. The following are some examples.

Viscosity

Viscosity is the tendency of a liquid to keep from flowing—its resistance to flowing.

viscosity

the degree to which something is thick, sticky, and semifluid in consistency, due to internal friction.

a quantity expressing the magnitude of internal friction, as measured by the force per unit area resisting a flow in which parallel layers unit distance apart have unit speed relative to one another.

One way to think about viscosity is to consider how "thick" a liquid is. Syrup is MORE viscous than water is.

The viscosity of a liquid usually decreases as its temperature goes up.

Conductivity

Conductivity is used to express how well a material allows heat or electricity to flow.

conductivity

the degree to which a specified material conducts electricity, calculated as the ratio of the current density in the material to the electric field that causes the flow of current. It is the reciprocal of the resistivity.

(also thermal conductivity)the rate at which heat passes through a specified material, expressed as the amount of heat that flows per unit time through a unit area with a temperature gradient of one degree per unit distance.

Materials that have high conductivity, such as metals, are called conductors.

Malleability

Malleability is the ability of a solid to be hammered without shattering.

malleable

(of a metal or other material) able to be hammered or pressed permanently out of shape without breaking or cracking.

Most metals malleable to a greater degree than are other things, like ice or glass.

Hardness

Hardness of a material relates to the degree to which its surface can be penetrated. For an object to scratch another object, it must be made of a material that has more hardness then the other.

hardness

a measure of how resistant solid matter is to various kinds of permanent shape change when a compressive force is applied.

Melting and Boiling Points

The melting point is the temperature at which a substance changes from solid to liquid. This same temperature is also the point at which the substance changes from a liquid to solid (freezing point).

The boiling point is the temperature at which a substance changes from a liquid to a gas. At this same temperature, gases condense into a liquid (condensation point).

Density

Density is the ratio of a substance's mass to its volume and can be expressed mathematically as D=M/V. Density results from the number of protons, neutrons, and electrons in the atoms that make up the substances and how closely they are arranged to each other either in the substance.

The physical properties of a material can be used to help identify it. A sample can be compared to known quantities to determine if the sample is made from them. For example, if an unknown metal has a density of 10.5 g/cm, it might be silver. If the other properties of the unknown match other known properties of silver, then the conclusion that the sample is sliver might be well-founded.

Separating Mixtures

Some physical properties can be used to separate mixtures. For example, a strong magnet could extract iron shavings from sand.

Other processes can be used with fluids.

Filtration

Filtration is a process that uses a porous material to separate substances based on the size of their molecules.

A sample of the substance is poured through a filter and the filtrate comes out. Large particles of a suspension will be deposited on the filter paper as a residue.

filtrate

a liquid that has passed through a filter

Evaporation

Evaporation is a process that will remove a liquid from a solution leaving behind the solid.

If a solutions is exposed to a temperature that is above the boiling point of the solvent, the solvent will turn to gas and leave the solute behind.

Evaporation is (one example) useful for separating a mixture of a solid and a liquid. 

Distillation

Distillation is a process that separates the substances in a solution based on their boiling points.

If a solutions is exposed to a temperature that is above the boiling point of the solvent, the solvent will turn to gas and leave the solute behind. 

 Distillation can separate a mixture of two liquids that have different boiling points such as alcohol and water.

Centrifugal Separation

A centrifuge can be used to separate a suspension into layers based on the density of the particles. Samples are exposed to strong centrifugal forces which causes the most dense particles to separate from the less dense particles.

Some physical properties can be changed. For example, hardness and viscosity will change when a substance goes from a solid to a liquid. Some changes are reversible. Others are not. Freezing and melting both can be reversed. Scratching or changing the shape (flattening) are not directly reversible.

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Definitions and content from:

New Oxford American Dictionary

Physical Science Concepts in Action, Pearson

http://en.wikipedia.org