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New Simplified Chemistry Class 7 ICSE Solutions – Physical and Chemical Changes

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New Simplified Chemistry Class 7 ICSE Solutions – Physical and Chemical Changes

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

Simplified ChemistryChemistryPhysicsBiologyMathsGeographyHistory & Civics

Points to Remember: 

  1. All changes are classified into two types
    • Physical change
    • Chemical change.
  2. Physical Change— A physical change is a temporary change in which no new substance is formed and chemical composition remains same. e.g. Melting of ice.
  3. Chemical Change— A chemical change is a permanent change, in which a new substance is formed whose chemical composition and physical properties are different, e.g. Burning of a candle.
  4. Chemical Reaction— Any chemical change in matter involving its transformation into one or more new substances is called a chemical reaction.
  5. Chemical Equations—A chemical equation is the symbolic representation of a chemical reaction using the symbols and the formulae of the substances involved in the reaction.
  6. The substances that react with one another are called reactants, and the new substances thus formed are called products.
  7. A balanced chemical reaction is one in which the number of the atoms of each element on the reactant side is equal to the number of atoms of that element on the product side.
  8. The law of conservation of mass states that mass can neither be created nor be destroyed.
  9. A chemical equation gives both qualitative and quantitative information about reactants and products.
  10. The type of chemical reaction in which two substances combine to form a new substance is known as combination reaction.
  11. The type of chemical reaction in which a substance breaks up on heating to form two or more simpler substances, which can be either elements or compounds, known as decomposition reaction. 

ACTIVITIES & DEMONSTRATIONS

Demonstrations & Discussions – By the Teacher
Classifying – changes into physical & chemical with the help of charts or match the following or by putting X
New Simplified Chemistry Class 7 ICSE Solutions - Physical and Chemical Changes 1

EXERCISE

Question 1.
Change is the law of nature and occur in our everyday life, at all times and in all places.
Differentiate between the following changes with a suitable example.
(a) Desirable and undesirable change.
(b) Periodic and non-periodic change
(c) Slow and fast change.
(d) Natural and man-made change
(e) Reversible and irreversible change.
Answer:
(a) Desirable and undesirable change
New Simplified Chemistry Class 7 ICSE Solutions - Physical and Chemical Changes 2
(b) Periodic and non-periodic change
New Simplified Chemistry Class 7 ICSE Solutions - Physical and Chemical Changes 3
New Simplified Chemistry Class 7 ICSE Solutions - Physical and Chemical Changes 4
(c) Slow and fast change.
New Simplified Chemistry Class 7 ICSE Solutions - Physical and Chemical Changes 5
(d) Natural and man-made change
New Simplified Chemistry Class 7 ICSE Solutions - Physical and Chemical Changes 6

(e) Reversible and irreversible change.
New Simplified Chemistry Class 7 ICSE Solutions - Physical and Chemical Changes 7
New Simplified Chemistry Class 7 ICSE Solutions - Physical and Chemical Changes 8

 

Question 2.
Differentiate between a physical change and a chemical change with reference to –
(a) Nature of change e. temporary and reversible or permanent and irreversible.
(b) Formation of products.
(c) Energy change taking place during the respective change.
Answer:
New Simplified Chemistry Class 7 ICSE Solutions - Physical and Chemical Changes 9

Question 3.
Give three reasons why melting of wax, is considered a physical change while burning of a candle, a chemical change.
Answer:
Melting of wax is a temporary and reversible change on cooling, wax solidifies and no new product is formed while burning of candle is a permanent change i.e. products are not convertible, new substance is formed having different composition & different properties.

Question 4.
State the observations seen, when milk in a dish is kept aside for a few hours or more. Is the change which occurs – a physical change or a chemical change. Give reasons.
Answer:
On keeping aside – the milk in a dish for a few hours or more. The change observed – will be that the milk has changed into curd. The change is permanent and cannot be reversed. New substance curd is formed. It is a chemical change.

Question 5.
State what is meant by the term – inter conversion of matter. Is inter conversion of matter a physical change or a chemical change.
Answer:
Inter conversion of matter involves, matter changing from one state to another and back to its original state, by change in temperature or pressure. It is a physical change in which one state of matter changes into another state and back again to its original state.

Question 6.
Ice kept in a beaker, slowly melts and turns into water. The water in the beaker on solidification Le. freezing turns back to ice. Give four reasons why the change from ice to water and water back to ice is considered a physical change.
Answer:
Both change are physical changes since

  1. The change is – temporary
  2. It is a reversible change
    [heating and cooling reverse the change]
    heating of ice – turns it into water,
    cooling of ice – turns    it back into  ice
  3. No new products are formed since both ice and water are chemically  – ‘H20’
  4. Properties of the original substance are not altered.

Question 7.
Explain the term – ‘sublimation’. Is sublimation of naphthalene – a physical or a chemical change. Give reasons.
Answer:
It is the conversion of a solid – directly into gaseous [vapour] state and on cooling directly back to solid state – without changing into liquid state.
It involves a change of state-and hence it is a physical change.

Question 8.
Ammonium chloride is also a sublimable solid. Give a reason why sublimation of ammonium chloride involves a physical and a chemical change.
Answer:
Sublimation of ammonium chloride – [NH4C1]
Ammonium chloride sublimes on heating and dissociates into ammonia [NH3] and hydrogen chloride [HC1], which recombine on cooling to give back – NH4C1
New Simplified Chemistry Class 7 ICSE Solutions - Physical and Chemical Changes 10
Dissociation – is a chemical change.
Hence, sublimation of such substances involves both – a physical and a chemical change.

Question 9.
State why addition of sodium chloride to water is considered a physical change, while addition of dilute sulphuric acid to zinc is considered a chemical change.
Answer:
Addition of sodium chloride to water is considered as a physical change because it does not form any new substance . but when addition of dilute sulphuric acid is added to zinc. They forms zinc-sulphate hence it is considered as a chemical change.

Question 10.
Photosynthesis is a natural process by which green plants manufacture food in the presence of sunlight.
(a) Are any new products formed during the above process.
(b) Can the change be reversed or is irreversible.
(c) State the conclusions which can be drawn, to represent photosynthesis as a physical or a chemical change.
Answer:
(a) The change is permanent and new products are formed – i.e. glucose and oxygen.
(b) The change cannot be reversed. It is irreversible.
(c) Carbon dioxide and water cannot be obtained back from glucose and oxygen hence it is chemical change.

Question 11.
Give reasons why – separation of mixtures e.g. iron from a mixture of iron and sulphur is a physical change, but heating a mixture of iron and sulphur is considered a chemical change.
Answer:
Physical change

  1. There is no change in the specific properties of the constituents.
    Example: The particles of iron can be separated from sulphur with the help of a magnet or by dissolving sulphur in carbon disulphide.
  2. No new substance is formed.
    Example: The mixture of iron and sulphur does not form any new substance.
  3. There is not net release or absorption of energy.
    Example: When iron and sulphur particles are mixed, heat energy is neither given out nor absorbed.
  4. It is a temporary change and can be reversed by removing the cause of the change.
    Example: The particles of iron can be separated from the mixture with the help of a magnet. removing the cause of change.

Chemical change

  1. There is a specific change in the prorperties of the – constituents.
    Example: The particles of iron or sulphur cannot be separated by a magnet or carbon disulphide.
  2. A new substance is formed.
    Example: Iron sulphide is the new substance formed when iron and sulphur are heated.
  3. There is a net release or absorption of energy when a chemical change takes place.
    Example: When iron sulphide is formed, the test tube gets red hot on account of the release of a large amount of heat energy.
  4. It is a permanent change and cannot be reversed by removing the cause of the change.
    Example: The particles of iron can be separated from the mixture with the help of a magnet.removing the cause of change.

Question 12.
Explain in brief the involvement of energy in – physical and chemical changes.
Answer:
Involvement of energy in physical and chemical changes

  1. Physical changes use energy to change the state of matter,
  2. Chemical changes release or absorb energy when changing a substance into a new substance.
    Energy is released during a decomposition of a substance while energy is absorbed during formation of a new substance.

Objective Type Questions
Physical & Chemical Changes

1. Fill in the blanks with the appropriate words for each of the statements given below:

  1. Germination of seeds is considered a chemical change
  2. If a change is permanent & irreversible it is considered a chemical change
  3. Heating a piece of iron, is considered a physical change, while heating a piece of coal [carbon] is considered a chemical change
  4. Chemical changes may involve exchange of energy in the form of light and heat.
  5. Change of milk of curd is a desirable change

2. State whether the following statements are true or false. If false write – the correct statement.

  1. Desirable changes are meaningful, while undesirable changes are unfavourable.
    True.
  2. During physical changes, the composition of the original substance is not altered, but the properties of the original substance are altered.
    True.
  3. During a chemical change the composition of the original substance is not altered and the change is irreversible.
    False.During a chemical change the composition of the original substance is altered and the change is irreversible.
  4. Melting of butter and wax are examples of chemical changes.
    False. Melting of butter and wax are examples of physical changes.
  5. Melting of ice is an exothermic, irreversible chemical change.
    False. Melting of ice is an endothermic, reversible physical change.

3. Match the examples of changes in List I with the correct.
New Simplified Chemistry Class 7 ICSE Solutions - Physical and Chemical Changes 11
Answer:
New Simplified Chemistry Class 7 ICSE Solutions - Physical and Chemical Changes 12
4. Fill in the blanks with the correct words for each of the statements given below:

  1. Sublimation is considered a change of state of matter.
  2. Sublimation involves a physical change
  3. During sublimation a solid on heating turns directly into vapour and on cooling back to solid.
  4. Ammonium chloride, a sublimable solid undergoes dissociation on heating.
  5. Sublimation of iodine is an example of physical change

5. Name the following:

  1. The product/s obtained during ‘photosynthesis’ – which is a chemical change.
    Ans. Glucose and Oxygen.
  2. The term involved in the change of state from – ‘water to ice’ – which is a physical change.
    Ans. Freezing Point.
  3. The final product of the physical change involved during ‘melting of a piece of wax’.
    Ans. Wax [CxHy]
  4. The type of change e. physical or chemical involved – ‘during respiration in human beings’.
    Ans. Chemical Change.
  5. The type of change physical or chemical involved – ‘when a substance undergoes a change in state, colour or size’.
    Ans. Physical Change.

New Simplified Chemistry Class 7 ICSE Solutions – Matter and Its Composition

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New Simplified Chemistry Class 7 ICSE Solutions – Matter and Its Composition

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

Simplified ChemistryChemistryPhysicsBiologyMathsGeographyHistory & Civics

Points to Remember:

  1. Matter has mass and occupies space.
  2. Matter is made up of atoms and molecules.
  3. Atoms are the smallest particles of matter which may or may not have independent existence.
  4. 4. Molecules are capable of independent existence. They are
  5. made up of atoms of same kind or different kinds.
  6. The atoms and molecules are in random motion.
  7. There are gaps between the molecules of matter called as intermolecular space.
  8. There exists a force of attraction between the molecules
  9. known as intermolecular force of attraction.
  10. Matter exists in three states : solids, liquid and gas.
  11. Matter can change from one state to another on changing temperature and pressure.
  12. The change of state of a matter from one form into another I is called inter conversion of states of matter.

EXERCISE

Question 1.
Explain the meaning of the term matter with special reference to the term ‘substance’.
Answer:
Matter is the basic substance of which all materials, living or non-living are made of.

Question 2.
Name the three states of matter. On what basis are the three states classified.
Answer:
Three states of matter are:

  1. Solid
  2. Liquid
  3. Gases

Basis of the classification are:
Physical properties like:

  1. Mass
  2. Volume
  3. Shape
  4. Rigidity
  5. Density
  6. Arrangement of particles.

Question 3.
Each of the three states of matter has mass. Explain with the help simple experiments – that each state of matter has mass.
Answer:
Matter i.e. solids, liquids and Gases have mass explained by the following experiments.
(1) Solid
Experiment: A solid placed on one side of the scale, causes the scale to tilt towards one side.
Conclusion: The scale tilts due to the mass of the solid, hence all solids have mass.
New Simplified Chemistry Class 7 ICSE Solutions - Matter and Its Composition 1

(2) Liquid:         
Experiment: A liquid placed on one side of the scale, causes the scale to tilt towards one side.
Conclusion: The scale tilts due to the mass of the liquid, hence all liquids have mass.
New Simplified Chemistry Class 7 ICSE Solutions - Matter and Its Composition 2

(3) Gas:
Experiment: An inflated balloon placed on one side of the scale causes it to tilt towards one side.
Conclusion: The scale tilts due to the mass of the gas, hence all gases have mass.
New Simplified Chemistry Class 7 ICSE Solutions - Matter and Its Composition 3

Question 4.
A measuring cylinder is filled with water to a particular mark. A piece of solid is immersed inside the measuring cylinder. State why the level of water in the measuring cylinder will rise up. If the solid is removed, what will be the new level of the water in the measuring cylinder. Give a reason for your answer.
Answer:
When a piece of solid stone is immersed inside the measuring cylinder. The water level rises up.
New Simplified Chemistry Class 7 ICSE Solutions - Matter and Its Composition 4
On removal of solid stone the water level in the measuring cylinder falls down back to the mark ‘A’.
New Simplified Chemistry Class 7 ICSE Solutions - Matter and Its Composition 5

Hence, It show that the stone occupies the space of the water and thus pushes the water level up. This experiment or procedure also proves that all solids occupy space.

Question 5.
A glass beaker is half filled with water and an empty glass tumbler is inverted & lowered inside the glass beaker. State your observations on tilting the tumbler below the level of the water in the glass beaker. Give a reason for your answer.
Answer:
(1) Take a glass beaker half-filled with water as shown in diagram.
New Simplified Chemistry Class 7 ICSE Solutions - Matter and Its Composition 6
(2) Take an empty glass tumbler which contains air is inverted and lowered inside the glass beaker.
New Simplified Chemistry Class 7 ICSE Solutions - Matter and Its Composition 7
(3) On tilting the tumbler the air inside the tumbler is displaced and bubbles of air are seen coming out. The air is pushed out by the water on tilting the tumbler inside the beaker of water.This experiment or procedure also proves that air or gases occupy space
New Simplified Chemistry Class 7 ICSE Solutions - Matter and Its Composition 8

Question 6.
Differentiate the general properties of solids, liquids and gases in the form of a table — with reference to
(a) mass (b) space  (c) volume (d) shape  (e) compressibility (f) density (g) free surfaces (h) diffusion.
Answer:
(a)
Solids— They have mass
Liquid — They have mass
Gases— They have mass

(b)
Solids— They Occupies space
Liquid— They Occupies space
Gases— They Occupies space

(c)
Solids-They have a definite volume
Liquid-They have a definite volume
Gases-They have no definite volume

(d)
Solids-They have a definite shape
Liquid-They have no shape
Gases-They have no shape

(e)
Solids-They have a no compressibility
Liquid-They have  slight compressibility
Gases-They have high compressibility

(f)
Solids-They have high density
Liquid-They have less density
Gases-They have least density

(g)
Solids-They have any number(of free surfaces)
Liquid-They have one free surfaces
Gases-They have no free surfaces

(f)
Solids-They have no diffusibility
Liquid-They have slight diffusibility
Gases-They have high proper diffusibility

Question 7.
State in which of the three states of matter- 
(a) Are the atoms or particles far apart
(b) The space between the particles is minimum.
(c) The force of attraction between the particles is very weak.
(d) The movement of the particles are neither about their own positions nor in any random direction.
Answer:
(a) Gas  (b)  Solid  (c)  Gas  (d)  Gas

Question 8.
Give a reason why –
(a) Solids have a definite volume & a definite shape.
(b) Liquids have a definite volume but no definite shape.
(c) Gases have no definite volume and no definite shape.
Answer:
(a)
Any matter that is a solid has a definite shape and a definite volume. The molecules in a solid are in fixed positions and are dose together. Although the molecules can still vibrate, they cannot move from one part of the solid to another part. As a result, a solid does not easily change its shape or its volume.
(b)
Any matter that is a liquid has a definite volume but no definite shape. The molecules in a liquid are less closely packed and they have space between them as compared to solids. Although the molecules can easily move. The inter molecular forces of attraction between the particles are less strong as compared to solids. Hence liquid does have fixed shape and takes the shape of the container in which it is placed e. It has definite volume.
(c)
Any matter that is a gas has no definite volume and no definite shape. The molecules in a gas are least closely packed and inter molecular space between them is very large when compared to solids & liquids. The inter molecular force of attraction between the particles are negligible. As a result a liquid does not easily change its shape nor they have fixed volume.

Question 9.
Particles of matter possess energy due to their random motion. Compare the particles in a solid, -liquid & in a gas with reference to the amount of kinetic energy possessed by each.
Answer:
Particles of matter possess energy due to random motion is called kinetic energy.
Comparison of particles in a solid, liquid and gas with reference to kinetic energy are given in the following:
New Simplified Chemistry Class 7 ICSE Solutions - Matter and Its Composition 9

Question 10.
Describe simple experiments to show that –
(a) particles of matter have inter molecular attraction
(b) particles of matter are closely packed in solids and less in liquids.
Answer:
(a) Experiment – To show that particles off matter have inter molecular attraction
New Simplified Chemistry Class 7 ICSE Solutions - Matter and Its Composition 10

Procedure:

  1. Globules of mercury are placed in a petri dish and kept at – a distance.
  2. The petri dish is shaken slowly and the mercury globules come together forming a big globule.
    Conclusion — The above experiment concludes that a force of attraction exist between particles of matter.

(b) Experiment – To show that particles are closely packed in solids and less in liquids

New Simplified Chemistry Class 7 ICSE Solutions - Matter and Its Composition 11

Procedure:

  1. Take a measuring cylinder and add 100 ml. of water to it.
  2. Add crystals of sugar [solid] to the water and stir carefully to obtain a sugar solution.
  3. The volume of water after addition of sugar remains the
    same i.e. at the 100 ml. mark.

Conclusion

  1. Particles of a liquid [e.g. water] are less closely packed.
  2. Particles of a solid [e.g. sugar] are closely packed.
  3. The sugar particles fill the inter molecular spaces, which must be existing between the water molecules and hence the level of water in the measuring cylinder does not rise.

Question 11.
A crystal of iodine is placed in a closed flat bottom flask and heated. State how you would conclude from the observations seen, that inter particle space is minimum in solids and maximum in gases.
Answer:
Procedure:

  1. 40 A crystal of iodine is heated in a closed flask. The crystal containing ‘X’ no. of particles turns into vapours, which also contain ‘X’ no. of particles and fills the complete flask.

Conclusion

  1. Particles of a solid [e.g. crystal of iodine] are more closely packed.
  2. Particles of a gas [e.g. vapours of iodine] are least closely packed and fill the flask completely.

New Simplified Chemistry Class 7 ICSE Solutions - Matter and Its Composition 12

Question 12.
Explain the term ‘inter conversion of matter’ – with ice as a starting material. State the term which refers to the conversion of a substance on heating from.
(a) solid state to liquid state
(b) liquid state to vapour state
(c) vapour state to liquid state
(d) liquid state to solid state.
Answer:
The phenomenon of change from one state to the other and then back to the original state without any change in its chemical composition is called ‘inter conversion of matter.’
The terms which refers to the conversion of a substance are:
(a) Melting
(b) Vaporisation
(c) Liquefaction
(d) Solidification

Question 13.
Give a reason why solids and liquids co-exist at their melting points.
Answer:
A substance exists in the solid state below its melting point and in the liquid state above its melting point. Hence, solids and liquids co-exist at their melting point.

Objective Type Questions
Matter and its composition

Question 1.
Match the characteristics of the three states of matter in List I with their correct answer from List II.
New Simplified Chemistry Class 7 ICSE Solutions - Matter and Its Composition 13
Answer:
New Simplified Chemistry Class 7 ICSE Solutions - Matter and Its Composition 14

Question 2.
Select the correct answer from the choice in bracket to complete each sentence:

  1. Matter is defined as anything that occupies space and has mass
  2. The three states of matter are classified on the basis of differences of certain physical.   
  3. Matter made up of one kind of particles is said to be homogeneous.
  4. Particles in a gas possess very large kinetic energy.
  5. The inter molecular force of attraction is maximum in solids.

Question 3.
Give reasons for the following.

  1. Gases have no definite shape or volume.
  2. Liquids have one free upper surface only.
  3. Globules of mercury kept in a petri dish, which is shaken slowly, come together forming a big globule.
  4. A crystal of iodine on slow heating in a closed flask, turns into vapours and fills the complete flask.
  5. An empty tumbler lowered into a glass beaker containing water, on tilting shows bubbles of air coming out, but when not tilted, no bubbles are seen.

Answer:

  1. Any matter that is a gas has no definite volume and no definite shape. The molecules in a gas are least closely packed and inter molecular space between them is very large when compared to solids & liquids. The inter molecular force of attraction between the particles are negligible. As a result a liquid does not easily change its shape nor they have fixed volume.
  2. Liquids have one free upper surface only because as liquids have a definite volume but no shape and while liquids are bounded by the container, they are placed in and have only one free surface, the upper surface.
  3. This is because the air is being pushed out by the water on tilting the tumbler inside the beaker of water. Air or gases occupy space.

Question 4.
State the correct term from A, B, C, D, E or F in List II which represents the – change of state of matter or its relevant property from List I
New Simplified Chemistry Class 7 ICSE Solutions - Matter and Its Composition 15
Answer:
New Simplified Chemistry Class 7 ICSE Solutions - Matter and Its Composition 16

Question 5.
Match the arrangement of atoms in the three states of matter in List I with the correct state in List II.
New Simplified Chemistry Class 7 ICSE Solutions - Matter and Its Composition 17
Answer:
New Simplified Chemistry Class 7 ICSE Solutions - Matter and Its Composition 18