class 7 worksheet on physical and chemical changes

PHYSICAL AND CHANGES.

 1. Classify the following changes as physical or chemical change:

        i. Rusting of iron

        ii. Burning of crackers

        iii Digestion of food

        iv. Melting of ice

        v. Chopping of vegetables

        vi. Respiration

        vii Growing of a seed into a plant

        viii Dissolving sugar in water

Q2) Define rusting. What are the conditions necessary for rusting?

Q3) What is rust? What is its chemical formula?

Q4) Define galvanisation. Why are the iron pipes in our homes galvanized?

Q5) Why does rusting take place faster near the coastal areas?

Q6) Explain two methods by which rusting of iron can be prevented.

 Q7. State True or False –

1. Melting of wax is a chemical change.
2. A physical change involves formation of new products.
3. A chemical change is irreversible.
4. Burning of paper is a chemical change.
5. Chemical change cannot be reversed by simple physical methods

8.   Name the metals involved in making stainless steel.

2    9.Write down the equation representing the process of rusting.

3   10.Identify the following as physical (P) or chemical (C) changes

4.    a. NaCl (Table Salt) dissolves in water. ______

5.   b Milk sours. _____

6.   c. Ag (Silver) tarnishes. ______

7.   d. Salt dissolves in water. _____

8.   e. An apple is cut. ______

9.   f. Wood rots. _____

1    g. Heat changes H2O to steam. ______

1    h. Pancakes cook. _____

1    i. Baking soda reacts to vinger. ______

      j. Grass grows. ____

1    k Fe (Iron) rusts. ______

1    l. A tire is inflated. _____

     m. Alcohol evaporates . ______

1    n. Food spoilage. _____

1    o. Ice melts. ______

       p. Paper towel absorbs water.