Difference Between Physical and Chemical Change

Main Difference – Physical vs Chemical Change

Physical changes occur without changing the chemical arrangement of a substance. Chemical changes occur by changing the chemical composition of substances. This is the main difference between physical and chemical change. Most of the physical changes include phase transitions where the phase or the state of matter is changed. Chemical changes occur during chemical reactions. Chemical reactions cause the changes of chemical composition of substances by either forming new chemical bonds or by breaking down existing chemical bonds.

Key Areas Covered

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

Key Terms: Chemical Change, Decomposition, Density, Irreversible, Phase Transitions, Physical Change, Reversible, Synthesis

What is a Physical Change

A physical change is the change of matter that occurs without changing the chemical composition of matter. In other words, physical changes affect the form of chemical substance without changing the chemical composition of it. Therefore, after a physical change, new substances are not formed.

A physical change of a substance may change its color, size, shape, etc. Sometimes the phase or the state of matter is changed. This is called phase transition. The major states of matter are solid state, liquid state, and gaseous state. The phase transition occurs when substances are cooled or heated. A physical change of matter changes the physical properties of a substance. For example, the phase transition of matter changes the density of matter.

Physical changes occur when heating or cooling is done. This can result in melting of a solid, vaporization of a solid or a liquid, condensation of vapor, crystallization, etc. Moreover, when two compounds are mixed, it can cause physical changes if there are no chemical reactions between the mixed substances.

Figure 1: Melting of Ice

Some examples of physical changes include melting an ice cube, formation of ice on water, dissolving of sugar in water, boiling water, mixing salt and sand, mixing water and oil, etc. Most physical changes are considered as reversible processes. Therefore, the initial compound can be obtained again.

What is a Chemical Change

A chemical change is the change of chemical composition of matter. Therefore, chemical changes are chemical reactions. Chemical reactions can cause changes in the chemical composition of matter. It results in the formation of new products. Chemical changes are often irreversible.

A chemical change can mainly be either a synthesis or a decomposition. Synthesis reactions include the formation of new products from initial reactants. Decomposition reactions also form new products from substances by breaking down into smaller compounds. Both these methods involve the breakdown of existing chemical bonds or the formation of new chemical bonds. Therefore, these chemical reactions require energy exchanges. This is because energy has to be provided from outside in order to break down existing bonds and formation of chemical bonds releases energy.

Figure 2: Releasing Air Bubbles is an Indication of a Chemical Reaction

Some examples of chemical changes include rusting of iron, burning wood, polymerization, vulcanization, combustion of fuel, digestion of substrates by enzymes, etc. Some chemical changes are visible to the eye whereas others are not visible. For example, some chemical changes show color changes, release of air bubbles, releasing odors, formation of precipitates, etc.

Difference Between Physical and Chemical Change

Definition

Physical Change: A physical change is the change of matter that occurs without changing the chemical composition of matter.

Chemical Change: A chemical change is the change of chemical composition of matter.

Nature

Physical Change: Physical changes are usually reversible.

Chemical Change: Chemical changes are usually irreversible.

Product Formation

Physical Change: New products are not formed during physical changes.

Chemical Change: New products are formed during chemical changes.

Energy

Physical Change: Some physical changes occur when heating/cooling is done.

Chemical Change: Chemical changes always involve absorption or release of energy.

Chemical Bonds

Physical Change: Physical changes have no effect on the chemical bonds of molecules of a substance.

Chemical Change: Chemical changes have a direct effect on the chemical bonds of molecules in a substance.

Conclusion

A substance can undergo physical and chemical changes. These changes can cause a substance to change its form or to change into a completely different substance. The main difference between physical and chemical change is that a physical change does not change the chemical composition of a substance whereas a chemical change changes the chemical composition of substances. 

References:

1. Helmenstine, Anne Marie. “Can You Name Examples of Physical Changes?” ThoughtCo, Available here.
2. Helmenstine, Anne Marie. “Examples of Chemical Changes We Experience Every Day.” ThoughtCo, Available here.
3. “Chemical change.” Wikipedia, Wikimedia Foundation, 18 Oct. 2017, Available here.

Image Courtesy:

1. “263823” (Public Domain) via Pixabay
2. “Chemical Reaction” by Kate Ter Haar (CC BY 2.0) via Flickr