WORKSHEET (CHEMISTRY) CH – 2 (PHYSICAL AND CHEMICAL CHANGE) 1) Change - is the law of nature which occurs in everyday life. State when a substance (i.e. matter) undergoes a kind of change. 2) Is change of state of matter – a physical or a chemical change? Give reasons. 3) Give a reason why – a. Freezing of water is a reversible change while burning of candle is an irreversible change. b. Change of seasons is a periodic change while change of weather is a non- periodic change. 4) State which of the following pertain to – chemical changes: a) Substance retains its identity. b) The change is permanent c) No new substance is formed. d) Is easily reversible e) Produces one or more new substances by change in its composition. f) The change is temporary. g) The composition and properties of the original substance are not altered. 5) Compare the energy changes involved during a physical or a chemical change. 6) State which of the following terms connected with change of state of matter i.e. – a) Meltingb) vaporizationc) condensationd) freezing pertains to – i. conversion of a liquid into a vapour or gas ii. conversion of a liquid into a solid iii. conversion of a solid into a liquid on heating 7) Potassium chloride is added to water and stirred. A salt solution is obtained which is then boiled leaving behind a residue. a) Is the above change physical or chemical? b) Is the change reversible or irreversible? c) Are the composition and properties of the original substance altered? d) Name the residue which remains behind after the salt solution is boiled. 8) Burning of a magnesium ribbon in air is considered a chemical change. Give a suitable reason behind the same. 9) Give a reason why- a) Heating of a platinum wire is a reversible change but heating a magnesium wire is an irreversible change. b) Addition of zinc nitrate to water is a physical change but addition of zinc to dilute nitric acid is a chemical change. c) Rusting of iron is a chemical change but magnetization of iron is a physical change. 10) Select the chemical change from the following list of changes:- I. Vaporization of water into water vapour II. Boiling of milk III. Respiration in mammals IV. Rotting of eggs V. Drying of a fruit VI. The carbon cycle VII. Occurrence of lightening VIII. Breaking of glass IX. Butter turning rancid X. Glowing of an electric bulb XI. Crystallization of a salt from its solution XII. Change of seasons XIII. Preparation of carbon dioxide from calcium carbonate and dilute hydrochloric acid. 11) Name the following: a) A form of energy required for a chemical change. b) The salt obtained when a chemical change takes place on addition of iron to dilute sulphuric acid c) The product obtained during a physical change when water converts from a liquid into a solid. d) The product of the chemical change on keeping a polished iron nail exposed to the atmosphere. e) The gaseous product of the chemical change which takes place during respiration of living organisms. 12) State which of the following 1 to 5 pertain to – a) Physical change b) Chemical change 1. Sublimation 2. Fermentation 3. Condensation 4. Magnetization 5. Respiration 13) Give reasons why the following are considered as chemical changes:- a. Copper carbonate on heat gives copper oxide and carbon dioxide b. A bright light is seen evolved when a strip of magnesium is heated c. Sulphur when burnt in air evolves a gaseous acidic product. d. An iron nail kept open in the atmosphere rusts. e. A piece of magnesium strip is dropped into a beaker containing dilute hydrochloric acid. 14) Select the correct answer from the choice in bracket to complete each sentence:- 1. A change in which a substance retains its identity is a __________________ (physical/chemical) change. 2. Matter is added or removed during a __________________ (physical/chemical) change. 3. Dissolution of lead nitrate in water is deemed as a __________________ (physical/chemical) change. 4. A change in which matter undergoes a change but the total mass of substance is unaltered is a __________________ (physical /chemical) change. 5. Energy required for completion of a physical change is ________________ (released/ absorbed) when the change is reversed. 15) Match the examples of changes in List I with the correct type of change in List II. S.No List I List II 1. Burning of paper A. Physical change 2. Ringing of an electric bell B. Chemical change 3. Curdling of milk 4. An electric light is switched on 5. Melting of Butter
Answers
Answers:
- Changes are of two types: physical changes and chemical changes. Changes in size or shape is physical change and in chemical changes a substance changes to a new substance with different properties.
Example of physical change are: tearing of paper, melting of ice, breaking of glass etc.
Example of chemical change: burning of paper, turning milk into curd.
2. It is physical change as no new substance is formed only the state changes. The properties are same.
3. a. When water freezes it changes to liquid to solid. The change is a physical change and is irreversible. This means it can be again converted to water by melting it. When we freeze it only the state changes but when we burn a candle chemical change takes place as the properties changes.
4. The correct answer is (e)Produces one or more new substances by change in its composition. In chemical two or more substances combine to form a new substance.
5. In physical changes no energy is required to initiate the change. While in chemical change energy like heat or light is required to initiate change.
6.Conversion of liquid into vapor or gas. - (b) Vaporization
Conversion of liquid into solid. - (d) Freezing
Conversion of solid into a liquid on heating. - (a) Melting
7. a) It is a physical change.
b) The change is reversible.
c) No, they are not altered.
d) The residue left between is potassium chloride.
8. It is a chemical change as it is irreversible change as the Magnesium changes to Magnesium oxide.
9. a) When platinum wire is heated only the color changes and when it cools the earlier colors comes but when magnesium wire is heated it changes to magnesium oxide and therefore it is a chemical change so irreversible.
b) Zinc nitrate dissolves in water so it is a physical change. The reaction between zinc and nitric acid produces H2 gas which gets oxidized causing a chemical change.
c) Iron rust has different properties from iron and has new properties, which cannot be reversed. Magnetization of iron is a temporary change, which does not change the composition of iron but only physical properties.
10. III Respiration in mammals
IV Rotting of eggs
VII Occurrence of lightning
IX Butter turning rancid
XIII Preparation of carbon dioxide from calcium carbonate & dilute hydrochloric acid
11. a) heat energy is required for a chemical change.
b) will be be formed as a result of the chemical change.
c) Ice is formed
d) Iron III oxide is formed.
e) Carbon dioxide is released.
12. 1. Sublimation -Physical Change
2. Fermentation -Chemical Change
3. Condensation- Physical Change
4. Magnetization- Physical Change
5. Respiration -Chemical change
13. a) New substances are formed with new properties. The change is irreversible.
b) When magnesium strip is burnt in air it changes to magnesium oxide. It burns with a bright white light and is an irreversible change.
c) Sulphur when burnt in air produces sulphur gas which is acidic and harmful. The properties differ and therefore the change is irreversible.
d) Iron when exposed to air reacts with air and changes to iron oxide. It destroys the iron and it can't be reversed.
e)Magnesium chloride is formed which has different properties from magnesium. Thus this is a chemical change.
14. 1. A change in which a substance retains its identity is a physical change.
2.Matter is added or removed during a chemical change.
3.Dissolution of lead nitrate in water is deemed as a physical change.
4. A change in which matter undergoes a change but the total mass of substance is unaltered is a chemical change.
5. Energy required for completion of a physical change is released.
15. Burning of paper - Chemical Change
2.Ringing of an electric bell Physical Change
3. Curdling of milk Chemical Change
4. An electric light is switched on -Physical Change
5. Melting of Butter- Physical Change
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Answers:
Physical and chemical changes are the two sorts of changes. Physical changes involve the transformation of a substance into a new substance with different qualities, whereas chemical changes involve the transformation of a substance into a new substance with distinct properties.
Paper tearing, ice melting, glass breaking, and other physical changes are examples of physical change.
Example of chemical change: burning of paper, turning milk into curd.
2. It is a physical change since no new substance is created; only the condition of the substance changes. The attributes are identical.
3. a.Water transforms from a liquid to a solid when it freezes. The transformation is a physical one that cannot be reversed. This means that by melting it, it can be transformed back to water. When we freeze something, only the state changes; but, when we burn a candle, the chemical properties change as well.
4. The correct answer is (e)Produces one or more new substances by change in its composition. In chemical two or more substances combine to form a new substance.
5. In physical changes no energy is required to initiate the change. While in chemical change energy like heat or light is required to initiate change.
6.Conversion of liquid into vapor or gas. - (b) Vaporization
Conversion of liquid into solid. - (d) Freezing
Conversion of solid into a liquid on heating. - (a) Melting
7. a) It is a physical change.
b) The change is reversible.
c) No, they are not altered.
d) The residue left between is potassium chloride.
8. It is a chemical change as it is irreversible change as the Magnesium changes to Magnesium oxide.
9. a) As platinum wire is heated, only the colour changes, and when it cools, the previous hues return, but when magnesium wire is heated, it transforms into magnesium oxide, which is an irreversible chemical change.
b) Because zinc nitrate dissolves in water, it undergoes a physical transformation. Zinc and nitric acid react to form H2 gas, which is then oxidised, resulting in a chemical change.
c) Iron rust has different properties from iron and has new properties, which cannot be reversed. Magnetization of iron is a temporary change, which does not change the composition of iron but only physical properties.
10. III Respiration in mammals
IV Rotting of eggs
VII Occurrence of lightning
IX Butter turning rancid
XIII Preparation of carbon dioxide from calcium carbonate & dilute hydrochloric acid
11. a) heat energy is required for a chemical change.
b) will be be formed as a result of the chemical change.
c) Ice is formed
d) Iron III oxide is formed.
e) Carbon dioxide is released.
12. 1. Sublimation -Physical Change
2. Fermentation -Chemical Change
3. Condensation- Physical Change
4. Magnetization- Physical Change
5. Respiration -Chemical change
13.a) New chemicals with new properties are created. The transformation is unstoppable
b) Magnesium strip burns to magnesium oxide when exposed to air. It emits a bright white light and is a permanent modification.
c) Sulphur creates sulphur gas, which is caustic and hazardous when burned in the air. Because the characteristics differ, the change is irreversible.
d) When iron is exposed to air, it reacts with it and forms iron oxide. It corrodes the iron and is irreversible.
e)Magnesium chloride is produced, which has characteristics that are not the same as magnesium. As a result, there has been a chemical shift.
14. 1. A change in which a substance retains its identity is a physical change.
2.Matter is added or removed during a chemical change.
3.Dissolution of lead nitrate in water is deemed as a physical change.
4. A change in which matter undergoes a change but the total mass of substance is unaltered is a chemical change.
5. Energy required for completion of a physical change is released.
15. Burning of paper - Chemical Change
2.An electric bell is ringing. Changes in Physical Form
3. Chemical Changes in Milk Curdling
4. A light bulb is turned on -Physical Change
5. Physical Changes in Butter Melting
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