Available Answers

1. 1.

   Identify the following as reversible or irreversible changes.

   1. Melting of wax
   2. Dissolving of salt in water
   3. Growth of a baby
   4. Cooking of food
   5. Growth of a plant
2. 2.

   What is an undesirable change? Give examples. 

3. 3.

   Why melting of ice is considered a reversible change?

4. 4.

   What is an endothermic change? Give examples. 

5. 5.

   Write/Choose the correct answer. 

   1. A physical change is temporary and ______.
   2. Chemical changes involve breaking if old chemical bonds which exist between the atom of reaching substances and then making new chemical bonds between the rearranged atoms to form new substances. (True/false)
   3. Germination of a seed is a ______ change. (chemical/physical)
   4. There is a change in the net ______ of the system during a chemical change. 
6. 6.

   Write/Choose the correct answer. 

   1. During a ____ change, a substance undergoes a change in its physical properties without any change in its composition. 
   2. A chemical change is temporary and reversible. (True/false)
   3. Burning is a ______ change. 
   4. When copper objects are left exposed to moist air, a brown flaky layer develops on their surface. ( True/False)
   5. During melting, the temperature keeps changing. (True/False)
   6. The rate of evaporation ______ with increase in temperature. 
   7. The process in which a solid directly changes into vapour on heating without passing through the liquid state is called ______. 
   8. Cooking of food is a change in which energy is absorbed. (True/False).