Question

Classify each of the following as a physical change or a chemical change. For each chemical change, explain how you can tell that a new substance has been formed.

a) Water boils and turns into steam.
Choose the correct option:
a) Physical change
b) Chemical change
c) Both physical and chemical changes
d) None of the above

Answer 1

Water boils and turns into steam is a physical change. When gasoline burns, it changes into different substances indicating a chemical change. Milk becoming sour involves several chemical changes.

Step-by-step explanation:

a) Water boils and turns into steam. Since steam is water in the gas phase, the boiling of water is a physical change.

b) When gasoline burns, it changes into different substances. This is a chemical change because new substances are formed.

c) When milk becomes sour, several chemical changes occur, such as protein denaturation, sugar breakdown, and acid production. The milk is now made up of different substances, so this is a chemical change.

d) Sugar dissolves easily into water, but it still remains sugar. If the water is evaporated, the sugar will recrystallize as a solid again. Dissolving is a physical change because the substance does not change.

e) Melting solid gold into liquid gold is a physical change similar to melting solid water (an ice cube) into liquid water.