Available Answers

1. 1.

   Write T for and F for False.

   1. A change in which the chemical composition of a substance changes is called a physical change.
   2. In a physical change, a considerable change of energy is involved.
   3. Cooking of rice is a reversible change.
   4. Melting of butter is a chemical change.
   5. Changing of iron and sulphur into iron sulphide on heating, is a chemical change.
2. 2.

   Fill in the blanks.

   1. Evaporation of river water is a/an ___________ (desirable/undesirable) endothermic change.
   2. Naphthalene balls changing into napthalene vapours is a/an _____________ (reversible/irreversible) change.
   3. Condensation of water vapour to form clouds is an ______________ (exothermic/endothermic) change.
   4. The process of mixing a substance uniformly with another substance to form a solution is called ____________ (sublimation/dissolving)
   5. During the evaporation process, the _____________ (solute/solvent) vaporises leaving behind the ______________ (solute/solvent)
   6. _____________ (High/Low) temperature, _____________ (large/small) surface area, _____________ (high/low) humidity, and fast-moving air increases the rate of evaporation.
3. 3.

   Categorize the following changes as desirable, undesirable, endothermic or exothermic.

   1. Curdling of milk meant for drinking.	2. Fermentation of fruit juice meant for drinking
   3. Burning of a car.	4. Burning of fuel
   5. Rusting of an iron gate.	6. Digestion of food

    

4. 4.

   Name the following.

   1. A change in which energy is released in the form of heat.
   2. A change in which the chemical composition of a substance undergoing the change remains the same
   3. A change that can be reversed
   4. A change which is not beneficial to us
   5. A change which takes place over a long period of time
5. 5.

   Give technical terms for the following.

   1. The process in which a liquid changes into a soft semi-solid mass.
   2. The process of breaking down of food to release carbon dioxide, water and energy.
   3. The process inn which a substance is decomposed by the action of microorganisms with the release of heat and carbon dioxide.
   4. The slow process in which iron changes to iron oxide.
   5. The process in which a substance changes from solid to gaseous state directly without forming the liquid state.
6. 6.

   Choose the correct option.

   1. Factor that decreases the rate of evaporation
      1. Low temperature
      2. High temperature
      3. Low humidity
      4. Fast wind
   2. Evaporation of water from an ocean is
      1. Exothermic
      2. Irreversible
      3. Undesirable
      4. Reversible and desirable
   3. Ammonium chloride crystals change into vapour form on
      1. Cooling
      2. Heating
      3. Rusting
      4. Dissolving
   4. Which one of these is not a sublime solid?
      1. Ammonium chloride
      2. Iodine
      3. Carbon
      4. Naphthalene
   5. Bursting of crackers is an exothermic change. It is also a
      1. Chemical change
      2. Irreversible
      3. May or may not be desirable
      4. All of these.