Question

Give Reason For the following:

Q1) Mixing of sand with water is a reversible change.

Q2) Mixing of cement with water is an irreversible change.

Q3) Burning of sugar is a chemical change.

Answer 1

Reversible changes are the change where the substances in the mixture don’t change.
while when one or more of the substances actually change then these are called Non-reversible and can’t return to what they were.
A chemical change is a change in which something new is formed (irreversible). The starting materials change into an entirely different substance or substances. This new substance has a different chemical composition than the starting materials.
Therefore we can account for the following changes:

a) Sand in water is reversible since it could be seived to separate.
b) cement in water is a chemically irreversible change, they react with each other to form concrete.
c) similarly when sugar is burnt, it is changed to some other substances (CO₂ and H₂O.)
hence it is a chemical change.