Available Answers

1. 1.

   Match the statements in List I with the possible type of change from List II.
   [more than one change from List II is possible]

   List I	List II
   The change
   a. Is temporary & reversible & the state of the substance changes without its fundamental nature undergoing any change.	A. Slow Change
   b. Takes place - over days or years.	B. Periodic change
   c. Takes place at - definite intervals of time.	C. Fast change
   d. Summer changes into winter.	D. Undesirable change
   e. Cannot be changed back into original reactants - by changing the conditions.	E. Irreversible change
   f. Hot afternoons - change to cool nights.	F. Non-periodic change
   g. An iron nail rusts.	G. Desirable change
   h. Milk turns sour on keeping.	H. Physical change
   i. Produces useless results & are brought about by man or nature.	I. Chemical change

    

2. 2.

   For each of the statements given below pertaining to physical or chemical changes, state whether the statement or diagrammatic representations given, pertains to - a physical change or a chemical change.

   1. The change is temporary in nature.
   2. The change is an irreversible change.
   3. No new substances are formed during the change.
   4. Energy is the form of light, pressure or heat is required for the change.
   5. The change is permanent in nature.
   6. One or more new products are formed during the change.
   7. Energy required for completion of the change - is release - when the change is reversed.
   8. The product formed during the change - gives back the reactant on the change of conditions.
   9. 
   10. No change in mass of each substance undergoing the change.
   11. 
   12. the total mass is unaltered during the change.
   13. Properties of the original substance are unaltered.
3. 3.

   Give reasons why the changes given below - diagrammatically are considered physical or chemical changes.

   1.  Expansion of a metal on heating
   2.  Heating a platinum wire
   3. Burning of a candle
   4.  Separation of a mixture by sublimation
4. 4.

   Give reasons why the changes given below - diagrammatically are considered physical or chemical changes.

   5.  Heating a mixture of iron & sulphur
   6.  Magnetising an iron nail
   7.  Addition of an acid to zinc
   8.  Rusting of an iron nail
5. 5.

   For each of the changes given below - state whether they are physical or chemical changes.

   1. Ripening of a fruit.
   2. Curdling of milk.
   3. Dissolution of potassium nitrate in water followed by evaporation of the salt solution.
   4. Addition of dilute sulphuric acid to sodium carbonate resulting in the evolution of carbon dioxide gas.
   5. Butter turning sour or rancid on keeping.
   6. Boiling of water in a pan,
   7. Burning of cooking gas [i.e. L.P.G.] in the kitchen.
   8. Respiration in human beings & animals.
   9. Adding a piece of sodium to cold water resulting in evolution of a gas & formation of sodium hydroxide.
   10. Drying of a wet paint, applied on a wall.
   11. Clotting of blood, after bleeding occurs from a cut on a finger.
   12. Smashing of a piece of glass, into small glass pieces.
   13. Fermentaion of substances.
   14. Rotting of eggs.
   15. Boiling of milk.
   16. Rain cycle.
   17. Sublimatio of iodine.
   18. Carbon cycle.
   19. Ringing of an electric bell.