Is a Physical or Chemical Change Making Milk Sour?

Because lactic acid, which has a sour taste, is produced as a result of milk souring, the process is categorised as a chemical change. Physical and chemical qualities have a close relationship with both physical and chemical changes.

At the molecular level, a chemical change takes place. A new material must be created and energy must be either absorbed or released in order for a change to be considered chemical. States of matter and energy are indicators of a physical shift. The arrangement of the molecules is changed, but the internal structure is unaffected.

Iron rusting (iron oxide is produced), burning gasoline (carbon dioxide and water are produced), and bread rising are examples of common chemical reactions (carbohydrates are converted into carbon dioxide).

Examples of physical changes include breaking glass, melting ice, crushing a can, and dissolving sugar in water, as well as any change in phase or state (sublimation, condensation, vaporisation, freezing, and melting). Generally speaking, a physical change can be defined as an alteration in texture, colour, or shape.

After a chemical change occurs, there is often some kind of proof that a new material was produced, such as sound, odour, gas production, heat absorption or production, colour change, or light. The materials at the beginning and finish of a physical transformation may look different, but their fundamental molecular makeup is the same.

Misha Khatri
Misha Khatri is an emeritus professor in the University of Notre Dame's Department of Chemistry and Biochemistry. He graduated from Northern Illinois University with a BSc in Chemistry and Mathematics and a PhD in Physical Analytical Chemistry from the University of Utah.


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