Chapter-2 Physical and Chemical Changes
NOTE: Accept (Q5.) and (Q8.) all other questions are to be done in class work copy.
Short-Answer Questions:
Q1.What are reversible changes? Which of the two ─the vaporisation of water and the
burning of paper ─is a reversible change?
A1. Changes are said to be reversible when the opposite change can be brought about
by reversing the conditions.
Out of the two changes the vaporisation of water is a reversible change.
Q2. What are irreversible changes? Which of the two ─the melting of ice and the
growth of a plant –is an irreversible change?
A2. Changes are said to be irreversible when the opposite change cannot be brought
about by reversing the conditions.
Out of the two changes the growth of a plant is an irreversible change.
Q3. Define a periodic change. Is rusting a periodic change?
A3. Periodic changes are those which take place at fixed intervals of time.
No, rusting is not a periodic change.
Q4. Define a nonperiodic change. Is the swinging of a pendulum a nonperiodic
change?
A4.Nonperiodic changes are those which do not take place at fixed intervals of time.
No, the swinging of a pendulum is not a nonperiodic change.
Q5. Classify the following into desirable and undesirable changes.(to be done in book)
a) The spoiling of food─ Undesirable change
b) The digestion of food─ Desirable change
c) The rotting of an egg─ Undesirable change
d) The decay of a dead animal in open air─ Undesirable change
Q6. Define a physical change. Is rusting a physical change?
A6. A change in which no new substances are formed and which can be reversed by
reversing the conditions is called a physical change.
No, rusting is not a physical change.
