Q27 E - Chemistry (OpenStax)

Question

Classify each of the following changes as physical or chemical: 

(a) condensation of steam

(b) burning of gasoline

(c) souring of milk

(d) dissolving of sugar in water 

(e) melting of gold

Step-by-Step Solution

Answer

1. Physical
2. Chemical
3. Chemical
4. Physical
5. Physical

Understanding what is physical and chemical change

Physical change is a type of change in which physical structure changes but chemical composition does not change.

Chemical change is a change in which chemical composition of a substance changes.

Analyzing the phenomenon (a), (b), (c), (d) and (e)

1. It can be reversed by evaporating, so it is a physical change.
2. It cannot be reversed, so it is chemical change.
3. Souring of milk cannot be reversed, so it is a chemical change.
4. Dissolving of sugar can be reversed using condensation and crystallization, so it is a physical change.
5. It can be reversed back on freezing, so it is a physical change.