Physical And Chemical Properties

Physical and Chemical Properties

Physical Properties • A physical property of a substance can be observed directly or measured with a tool without changing the composition of the substance.

Chemical Properties • A chemical property involves the substance to undergo a change that will alter the composition of the substance.

What are some examples of physical properties? • • • • •

Boiling point, freezing/melting point Density Solubility Viscosity Electrical Conductivity

Boiling Point and Freezing/Melting Point • The terms boiling point and freezing/melting point DO NOT refer to the phase change itself but to a measurement: the temperature at which these changes occur. • The composition of a substance does not change during a phase change.

Density • Density is a measure of the mass per unit volume. • density=mass/volume • The density of a particular substance is always the same under constant conditions. • The density of a substance is different at different phases (solid, liquid, gas) • This is because the different phases have different volumes.

Density

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Solubility • A substance is soluble in a solvent if it will dissolve in that solvent. • Solute - the substance being dissolved • Solvent - what the substance is being dissolved in • Solubility is the maximum amount of solute that can dissolve in a given volume of solvent at a particular temperature and pressure.

Solubility (cont.) • A saturated solution is one in which the maximum amount of solute is dissolved in the solvent at a particular temperature. • Solutions (and therefore mixtures) do not chemically combine to form a new substance and therefore, solutions are composed of two substances which each retain their own properties. • Solubility is a physical property.

Solubility

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Viscosity • Viscosity is a property of fluids • Viscosity is a measure of the material’s resistance to flow. High-viscosity fluids take longer to pour than low-viscosity fluids. • Viscosity may change with temperature. • The composition of a fluid does not change when it is poured so viscosity is a physical property.

Electrical Conductivity • Solids are electrical conductors or insulators based on the solids ability to complete an electric circuit. • Materials (such as metals) with high conductivity are called electrical conductors because they allow current to flow easily. • Materials with low conductivity block current from flowing and are called electrical insulators. Most nonmetals are insulators.

Electrical Conductivity • Some solutions can conduct electric current, depending on the nature of the solute. • Solutes that allow electric current to flow are called electrolytes. • Electrolyte solutions contain ions.

What are some examples of chemical properties? • The ability to oxidize • The ability to corrode • Combustibility

The Ability to Oxidize • When oxidation occurs, a substance combines with oxygen to form a new substance with new properties. • The new substance formed is a combination of the atoms of the original substance and oxygen • The properties of a substance change during the process of oxidation

The Ability to Corrode • Corrosion is the process by which metals naturally combine with oxygen, sulfur, or other nonmetals. • Understand that when corrosion occurs, the new substance that is formed is a combination of a metal and a nonmetal. • Understand that the properties of a substance change during the process of corrosion

Combustibility • Combustion is a special type of oxidation. • When combustion occurs, a substance combines with oxygen to form a new substance with new properties in a process which releases heat and light. As in all cases of oxidation, the new substance which is formed is a combination of the original substance and oxygen • The properties of a substance change during the process of combustion.