Class 7 Physical Chemical Change

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Tick The Correct Answer

  1. A chemical reaction in which heat is absorbed

(a) endothermic

(b) exothermic

(c) (a) and (b) both

(d) none of these

  1. An oxidation reaction involves

(a) addition of hydrogen

(b) removal of hydrogen

(c) addition of oxygen

(d) (b) and (c) both

  1. Rusting of iron occurs in presence of

(a) air only

(b) air and moisture both

(c) moisture only

(d) a, b and c

  1. A chemical reaction in which a compound breaks into two or more substances is called

(a) double decomposition

(b) formation reaction

(c) neutralisation reaction

(d) decomposition reaction

  1. Rusting can be prevented by

(a) galvanization

(b) browning of apple

(c) evaporation

(d) all of the above

Ans.

  1. (a) endothermic
  2. (d) (b) and (c) both
  3. (b) air and moisture both
  4. (a) double decomposition
  5. (a) galvanization

Fill in the blanks :

  1. The chemical formula of iron oxide is———-
  2. The substances that are formed as a result of the chemical reaction are called—-
  3. The burning of paper is a————- change.
  4. Common salt is recovered from seawater by———— followed by

5.—————- have a definite volume but not a definite shape.

  1. Rusting takes place in the presence of moisture and—————–.

 Ans. 

  1. Fe2O3H2O
  2. product
  3. chemical
  4. evaporation
  5. Liquid
  6. air

 Short Answer Type Question :

  1. Give two differences between oxidizing and reducing agents along with examples.

Ans. The oxidizing agent is the substance which helps in addition of oxygen or removal of hydrogen from the substance being oxidised.

Example: Magnesium dioxide, oxygen, chlorine, potassium permanganate, bromine, Iodine  Reducing agent is the substance which helps in addition of hydrogen or removal of oxygen from the substance being reduced.

Example: Hydrogen, carbon, sodium, Potassium, hydrogen sulphide, sulphur dioxide

  1. What type of change is photosynthesis?

Ans.  Photosynthesis by plants is a process of  chemical change

  1. What is oxidation? Explain by giving one chemical reaction.

Ans. A chemical reaction that involves the addition of oxygen to a substance or removal of hydrogen from a substance is known as an oxidation reaction. When magnesium reacts with oxygen to form magnesium oxide it is said that magnesium is oxidised by gaining oxygen.

2Mg             +     O2     →         2MgO

Magnesium    Oxygen           Magnesium oxide

  1. What is decomposition reaction?

Ans. A decomposition reaction is one in which a compound breaks up into two or more simple substances.

Decomposition reactions are generally caused by heat, light, electricity and so on.

AB→ A + B

(1) When Calcium carbonate is heated, it decomposes into calcium oxide and carbon dioxide.

CaCO3—————- Heating—-    CaO         +           CO2

Calcium carbonate                   Calcium oxide            Carbon dioxide

(2) Silver Iodide decomposes in the presence of light to form silver.

2AgI       —–Light—-    2Ag  +               I2

Silver iodide                 Silver                iodine

 Physical And Chemical Change

 


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Summative Assessment – II