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Subject:

science-physics

Class:

class VII

Key Concepts

Chemical changes, Physical change, chemical and physical reaction, rusting, galvanization , crystallization

essential questions

1.What are the characteristics of physical and chemical changes?
2. What evidence do each of these changes show to indicate that they have occurred?
3. How does water and air bring in physical and chemical changes in various substances?

Remembering:

  1. A change in which original substance can be obtained back by change of conditions is called: a) reversible change  b) physical change  c) Chemical change  d) Both a and b
  2.  When magnesium is burnt, heat and light are produced. The burning of magnesium is a: a) reversible change  b) Physical change c) chemical and exothermic change  d) Chemical and endothermic
  3. Change of milk to curd is: a) Physical  b) chemical  c) Both physical and chemical  d) neither physical nor chemical
  4. Which of the following statement is correct: a) Evaporation is a chemical change  b) Digestion of food is chemical change  c) Burning of paper is a physical change  d) all of the above
  5. An oxide of iron from the following is : a) mud  b) dust  c) rust  d) none
  6.  Which of the following is not a mixture: a) air   b) Pure water  c) sea water  d) lemonade
  7. What is the formula of rust: a) Fe3O4  b) Fe2O3  c) Fe O  d) None

understanding:

  1. The process used to prevent rusting of iron, in which a thin coat of zinc is provided over iron surface. The process is: a) Galvanization  b) electroplating  c) painting in zinc  d) None
  2. Chemical Change that is accompanied by evolution of heat energy is: a) Physical chemical change  b) Exeothermic  c) endothermic  d) none
  3. Expansion of heating and contraction on cooling of metals is a: a) Chemical change b) physical  c) irreversible  d) None
  4. Hydrochloric acid is added to a beaker containing a piece of zinc. Zinc Chloride is formed and hydrogen gas is released: a) Chemical reaction  b) Physical change  c) Crystallization d) None
  5. The reason for a physical change to be named as such is that the: a) change occurs only in physical properties  b) transfer of energy takes place is a reversible one  c) transfer of energy takes place is a reversible one  d) all of the above
  6. When ice is heated, it changes to water and water on further heating gets converted to steam what happens when steam in condensed: a) a new substance is formed b) No new substance is formed  c) Gaseous phase changes to liquid phase  d) Both b and c are correct

Application:

  1. Hina took a candle in a vessel and heated the vessel. Even though the candle did not burn, it changed its shape and state. What kind of change is this? a) irreversible  b) physical change  c) chemical change  d) none
  2. Complete the following equation of rusting iron: a) Iron ( Fe) + A + Moisture → B  a) A= oxygen  B= carbon dioxide   b) A = water   B= oxygen   c) A= oxygen  B= rust   d) A= carbon dioxide   B= Oxygen
  3. Which of the following will happen when apple is left and exposed to air: a) It undergoes oxidation and becomes brown in color  b) Appearance of brown color on the surface of apple slice is caused by a chemical reaction  c) Both are correct   d) None

Analysis:

Look at the diagram:

Rusting of iron nail will be faster in which of the following test tubes:

a) A     b) B  c) Both A and B   d) Equal in A, B, C

Evaluation:

  1. The questions in this segment consists of two statements, one labelled as Assertion A and Reason R are individually true and if so whether the reason is a correct explanation of the assertion: Assertion A: Tearing of paper sheet into small pieces is a chemical change. Reason R: It is not possible to rejoin small pieces of paper to get back original paper sheet. a) Both A and R are true and R is the correct explanation of A. b) Both A and R are true but R is not the correct explanation of A. c) A is true but R is false. d) A is false but R is true
  2. Assertion A: Formation of rust is a chemical change. Reason R: For formation of rust, iron must be exposed to air and water. a) Both A and R are true and R is the correct explanation of A. b) Both A and R are true but R is not the correct explanation of A. c) A is true but R is false. d) A is false but R is true
  3. Assertion A: Burning of a candle is a physical change. Reason R: The product formed by burning a candle cannot easily be converted back to original candle. a) Both A and R are true and R is the correct explanation of A. b) Both A and R are true but R is not the correct explanation of A. c) A is true but R is false. d) A is false but R is true
  4. Assertion A: Burning of paper is a physical change. Reason R: The products formed on burning of paper cannot be converted back to paper. a) Both A and R are true and R is the correct explanation of A. b) Both A and R are true but R is not the correct explanation of A. c) A is true but R is false. d) A is false but R is true
  5. Assertion A: Coating an iron sheet with a layer of zinc is called galvanization. Reason R: the process which converts iron to iron ore oxide in the presence of moisture and air is called rusting. a) Both A and R are true and R is the correct explanation of A. b) Both A and R are true but R is not the correct explanation of A. c) A is true but R is false. d) A is false but R is true
  6. Assertion A: Explosion of a fire is a physical change  Reason R: A physical change is a reversible change. a) Both A and R are true and R is the correct explanation of A. b) Both A and R are true but R is not the correct explanation of A. c) A is true but R is false. d) A is false but R is true
  7. Complete the blanks with the right terms:

a)  Electrolyzing:____:: Crystallization: ____

b) Rusting:_____:: condensation of water:_____

c) depositing of zinc on iron:____:: crystal formation:_____

Create: