Difference Between Physical and Chemical Properties

Main Difference – Physical vs Chemical Properties

Properties of matter can be divided into two broad categories as chemical properties and physical properties. If the chemical composition of a substance is changed when a particular property is changed, then that property is a chemical property. But if the changes of a property do not change the chemical composition of the substance, then that property is a physical property. The main difference between physical and chemical properties is that physical properties can be observed without changing the chemical composition of a substance whereas chemical properties can be observed by changing the chemical composition of a substance.

Key Areas Covered

1. What are Physical Properties
      – Definition, Examples
2. What are Chemical Properties
      – Definition, Examples
3. What is the Difference Between Physical and Chemical Properties
      – Comparison of Key Differences

Key Terms: Appearance, Boiling Point, Chemical Properties, Extensive Properties, Intensive Properties, Melting Point, Physical Properties, Properties

What are Physical Properties

Physical properties are properties that can be measured without changing the chemical composition of matter. These properties can be used to describe the appearance and dimensions of matter. These physical properties can also be used to observe and compare different forms of matter.

Physical properties can be found mainly in two types as intensive properties and extensive properties. Intensive properties are physical properties that do not depend on the amount of substance. Extensive properties depend on the amount of substance. This means extensive properties change when the amount of the substance is changed.

Properties regarding the appearance of substance are intensive properties. For example, color is an intensive property. Melting point and boiling point of a substance are fixed (measured as standard values) values that depend only on the type of substance, not on the amount of substance. Density is also an intensive property that does not depend on the amount of substance because it is determined as the mass of a unit volume.

Figure 1:  Blue Color of Copper Sulfate is one of its Physical Properties

Extensive properties depend on the amount of substance that is being considered. These properties change when the amount of matter is changed. For example, mass is a physical property because it is measured without altering the chemical composition of a substance. Mass is an extensive property since it is a measure of the amount of substance. Likewise, volume, length or other dimensions that are changed when the amount of matter is changed are considered as extensive properties.

What are Chemical Properties

Chemical properties are properties that can be measured by changing the chemical composition of a substance. The chemical composition of a substance is like the identity of that substance; if the chemical composition is changed, the substance becomes a different substance. Chemical properties measure the chemical changes that a substance may undergo when it is subjected to a chemical reaction. Therefore, the structure of the sample must be altered for the chemical properties to become apparent.

Chemical properties of matter can be determined by observing the reactions of substances towards acids, bases, water or other chemicals. For example, if a particular substance can react with an oxidizing agent or a reducing agent, then the oxidation state of the elements in that substance is changed. Hence oxidation state is a chemical property. Likewise, there are many other chemical properties such as reactivity of elements, electronegativity, coordination number, enthalpy of combustion, etc.

Figure 2: Reactivity of Some Metals

Chemical properties of a substance have a strong relationship with the chemical bonds present in that substance. In order to alter the identity of a substance, we have to either form new chemical bonds or break down existing chemical bonds. Therefore, observing chemical properties will always include energy exchanges between the substance and the surrounding.

Difference Between Physical and Chemical Properties

Definition

Physical Properties: Physical properties are properties that can be measured without changing the chemical composition of matter.

Chemical Properties: Chemical properties are properties that can be measured by changing the chemical composition of a substance.

Chemical Composition 

Physical Properties: Physical properties can be measured without changing the identity of a substance.

Chemical Properties: Chemical properties are measured by changing the identity of a substance.

Chemical Bonds

Physical Properties: Physical properties do not have a direct relationship to the chemical bonds of a substance.

Chemical Properties: Chemical properties have a direct relationship to chemical bonds.

Amount of Substance

Physical Properties: The physical properties may or may not depend on the amount of the substance.

Chemical Properties: The chemical properties do not depend on the amount of the substance.

Examples

Physical Properties: Examples for physical properties include mass, density, color, volume, etc.

Chemical Properties: Examples for chemical properties include reactivity of chemicals, oxidation state, coordination number, etc.

Conclusion

Physical and chemical properties of substances are very important in identifying and studying chemical compounds. Physical properties are different from chemical properties of a substance. The main difference between physical and chemical properties is that physical properties can be observed without changing the chemical composition of a substance whereas chemical properties can be observed by changing the chemical composition of a substance.

References:

1. “Physical and Chemical Properties of Matter.” Chemistry LibreTexts, Libretexts, 21 July 2016, Available here.
2. Helmenstine, Ph.D. Anne Marie. “Learn What Chemical Properties Are and Get Examples.” ThoughtCo, Available here.
3. “Physical property.” Wikipedia, Wikimedia Foundation, 9 Oct. 2017, Available here.

Image Courtesy:

1. “Copper Sulfate Crystals” By Crystal Titan – Own work (CC BY-SA 4.0) via Commons Wikimedia