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Subject:

science-chemistry

Class:

class VI

Key Concepts

changes, evaporation, contraction, expansion, melting

essential questions

1. What happens to the particles when liquid water changes to a solid?
2. What is a physical change?
3. How are physical and chemical changes alike and different?
4. How is a chemical change different from a physical change?

Remembering:

  1. Give two examples of irreversible changes.
  2. Give two examples of slow changes.
  3. Give an example of reversible change.
  4. Name the process in which solid directly changes into vapor.
  5. Give an example of chemical change
  6. List the different forms of changes noticed.
  7. Define reversible change.
  8. State the list of changes caused due to heating.
  9. Define evaporation.
  10. List the characteristics of physical change.
  11. Define contraction.
  12. The melting of wax is an example of: a) physical change  b) chemical change   c) reversible change  d) both a and c
  13. Burning of candle is a : a) physical change   b) chemical change  c) periodic change   d)  both a and b
  14. When a woolen yarn is knitted to get a sweater, the change can be classified as:  a) physical change  b) chemical change   c) exothermic change  d) endothermic change
  15. The change of milk to curd, when we add a small quantity of curd to milk, can be classified as: a) fast change  b) slow change  c) periodic change  d) none of these
  16. Which of the following are endothermic change: a) condensation and melting  b) condensation and freezing  c) evaporation and melting  d) evaporation and freezing
  17. Which of the following is a periodic change: a) change of season   b) phases of moon  c) beating of human heart   d)  all of these

understanding:

  1. Can you change the shape of a eraser after erasing?
  2. What kind of change is breaking of wood?
  3. Write the difference between reversible and irreversible changes.
  4. Paheli is writing some sentences and choose the sentences which cannot be reversed: a)  heating of an iron   b) baking of chapatti   c) formation of ice from water  d) none of the above
  5. In which of the following sentences is or are cannot be reversed?   a) mixing of cement and water    b)mixing of plaster of paris and water   c) baking of clay brick   d) all the above
  6. Boojho is doing some activities with his family and friends. Choose which cannot be reversed?  a) mother heated oil in pan  b) making some flowers by paper folding c) candles are lit and put out  d) making dough balls by his mother
  7. Which of the following changes cannot be reversed?  a) blowing of a balloon b) folding a paper to make a toy aero plane  c) rolling a ball of dough to make roti  d) baking cake in an oven
  8. Iron rim is made slightly smaller than the wooden wheel. The rim is usually heated before fixing into the wooden wheel because on heating the iron: a) expands and fits onto the wooden wheel  b) contracts and fits onto the wooden wheel  c) no change in the size takes place  d) expands first, then on cooling contracts and fits onto the wooden wheel
  9. A chemical change is one which occurs with a) the formation of new substances  b) the evolution or absorption of energy  d) none of these
  10. A change is called physical change because in it: a) only change in physical properties takes place  b) transfer of energy takes place   c) can be easily reversed  d) all of the above
  11. Select the one that is a chemical change: a) rusting of iron  b) tearing of paper  c) both of these  d) none of these
  12. Select a reversible change: a) milk to paneer  b) growth of a tree  c) cow dung to biogas  d) ice cream to molten ice cream
  13. Which one is a periodic change:  a) earthquake  b)  formation of rainbow in sky  c) occurrence of tides in seas  d) none of these
  14. The change of a ball of dough to a rolled out roti is a : a) physical change   b) chemical change   c)  periodic change  d) none of these
  15. The change of kneading wheat flour into a dough is a: a) physical change   b) chemical change   c)  periodic change  d) none of these
  16. An airplane was cut out from a rectangular sheet of paper. The change involved is a: a) physical change  b) temporary change  c) irreversible change  d)  none of these
  17. Which of the following is a reversible change: a) ripening of fruit  b) melting of ice  c) burning of paper  d) converting wood into saw dust
  18. What kind of change is earthquake: a) periodic   b) non periodic   c) physical   d) none of the above

Application:

  1. Why is stretching of a rubber band a reversible change?
  2. Burning of paper is an irreversible change. Explain
  3. Look at the picture given below. What kind of change is shown in the picture? Choose the correct option. a) irreversible change, melted wax cannot be solidified again   b) reversible change, melted wax can be solidified again  c) periodic change, candle melts after an interval of an hour  d) chemical change, melting of candle wax results in change in composition of candle
  4. Payel is writing some sentences about changes. Choose the statement where you can say that the statements is or are correct about changes: a) the grinding of wheat to form flour is an irreversible change  b) formation of curd from milk is an irreversible change  c) the burning of paper is an irreversible change   d)all the above
  5. Boojho appeared in class test where he wrote some statements but he confused to know the statements which are related to “reversible changes”. Would you help him to know that? a) cow dung to biogas  b) making cheese paneer from milk  c )weathering of rocks  d) folding of dress to pass through a waterlogged area
  6. Why is spoiling of food considered a chemical change: a) In it the food changes from one chemical substance to another  b) it is not possible to get original food from spoiled food   c) it is permanent change  d) all of the above

Analysis:

  1. When is a change said to have taken place in a material? Give example.
  2. Which of the following is a  reversible change: a) change of raw egg to boiled egg   b) change of stretched rubber  band to its normal size  c) change of bud to flower  d) none of these
  3. Paheli is writing some sentences about changes as “some changes are beneficial to us whereas some are harmful to us”. Consider the sentences and choose the incorrect statement: a) the ripening of fruits is a beneficial change  b) the spoiling of cooked food is a harmful change  c) heat is the cause of the change of state of ice from solid to liquid  d) melting of wax is an irreversible change
  4. Conversion of ice cream to molten ice cream and cold milk to hot milk is an example of change which can be reversed. choose the statement where you can say that the statements is or are correct about changes: a) folding of paper is an irreversible change b) the cutting of paper is an irreversible change c) the rolling of roti out of dough is an irreversible change  d) the baking of clay pot in an oven is reversible change
  5. An iron ring is heated. which of the following statement about it is incorrect? a)  the ring expands  b) the ring almost comes to the same size on cooling c) the change in this case is reversed d) the ring changes its shape and the change cannot be reversed
  6. Condensation is a physical change, why: a) vapor turns into liquid   b) no heat is required  c) it happens automatically  d) no new substance is formed
  7. Choose the correct alternative to complete the given analogy. Physical change: boiling :: chemical change:___  a) melting   b) burning   c) condensing  d) evaporating
  8. Change in period of a school: periodic change:___: non periodic change  a) heart beating   b) formation of day and night  c) forest fire  d) change in phases of moon
  9. Find the odd one out: a) cutting of nails   b) breaking of glass  c) formation of ash from paper   d) tearing of paper
  10. You  are to examine the two statements carefully and decide if the Assertion A and Reason R are individually true and if so whether the reason is a correct explanation of the assertion. Select your answer to these items using codes given below: Assertion A: the explosion of a fire cracker 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
  11. Assertion A: The process of conversion of liquid water to its vapors by heating the liquid is called boiling. Reason R: The process of conversion of water vapor to liquid by cooling the vapors is called condensation. 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
  12. Assertion A: Burning of paper is a physical change. Reason R: The products formed on burning of paper cannot be easily 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
  13. Assertion A: The formation of rust is a chemical change. Reason R: For the 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
  14. Assertion A : Respiration is an exothermic process  Reason R: In an exothermic process heat is  evolved. 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
  15. Assertion A: The change of water from liquid to steam on heating is a physical change. Reason R: conversion of liquid into steam is called evaporation 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
  16. Read the following two statements carefully and choose the correct option. Statement 1: Rusting of iron is a chemical change. Statement 2: The change of liquid water to ice on cooling is a reversible change  a) Statement 1 is correct while statement 2 is also correct  b) Statement 2 is correct while statement 1 is incorrect  c) both statements are correct   d) both statement are incorrect
  17. Statement 1: Change of liquid water to steam, on boiling , is an irreversible change  Statement 2: Beating of human heart is a non periodic change   a) Statement 1 is correct while statement 2 is also correct  b) Statement 2 is correct while statement 1 is incorrect  c) both statements are correct   d) both statement are incorrect
  18. Do you think we break molecules when we turn chalk into chalk powder: a) yes, chalk powder is formed by breaking chalk into small pieces  b) yes, because formation of chalk powder is a chemical change   c) no because no new substance is formed molecules of  chalk and chalk powder are same   d) yes, because chalk is bigger in size than particles of chalk powder
  19. A very hot glass on putting under cold water cracks. This change is due to: a) expansion  b) contraction c) formation of new substance  d) none of these

Evaluation:

  1. Which of the following represent A :  a) solar eclipse  b) formation of rainbow  c) occurrence of season  d) both a and c
  2. Which of the following represent D: a) making tea  b) burning of sulphur  c) dissolving salt in water  d) burning of coal
  3. Seema and her sister had a discussion on whether heating of water in pan is a chemical or physical change. Seema’s sister said that its a chemical change as the water molecules just expand and become vapor. Is she correct? a) Yes, as its a chemical change and reversible   b) No, its a physical change and irreversible   c) Yes, its chemical change and irreversible  d) No, its a physical change and is reversible
  4. Look at the following diagram and answer the following question. Which of the following represents P and Q respectively:   a) Crushing of ice, melting of ice   b) cooking of food, bursting of cracker  c) explosion of a bomb, freezing of water to ice  d) melting of ice, burning of coal
  5. Anaerobic bacteria digest waste and produce biogas (change A). The biogas is then burnt as fuel (change B). The following statements pertain to these changes. Choose the correct one: a) Process A is a chemical change  b) Process B is a chemical change  c) Both processes A and B are chemical change  d) none of these processes is a chemical change
  6. On which of the following cases heat energy is released. A-When ice melts B- When water freezes to ice C-When water vapor condenses into liquid water D- When water evaporates into water vapor  a) A, B and C  b) B, C and D  c) B and C   d) all of these

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