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Comparison between physical and chemical changes - class-VII

Description: comparison between physical and chemical changes
Number of Questions: 30
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Tags: chemistry physical and chemical changes chemical reactions and their types is matter around us pure chemical reaction chemical changes chemical reactions phenomena around us change around us
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Identify the physical change:

  1. Photosynthesis

  2. Respiration

  3. Digestion of food

  4. Melting of Wax


Correct Option: D
Explanation:

Melting of wax is a physical change. In a burning candle there are both physical and chemical changes. The burning of the solid wax to form liquid wax and the evaporation of liquid wax to form wax vapour are physical changes. The burning of wax vapour is a physical change.

Which of the following represents a physical change?

  1. Stretched rubber band

  2. Melting of ice cream

  3. In winter, hair oil freezes.

  4. All of the above.


Correct Option: D
Explanation:

All of the following represents a physical change.
Stretched rubber band.
Melting of ice cream.
In winter, hair oil freezes.

Which of the following is/are true?

  1. When a metal rod is cooled, it expands.

  2. During expansion, the length of metal rod decreases.

  3. Both of the above.

  4. None of the above.


Correct Option: D
Explanation:

When a metal rod is heated, it expands. During expansion, the length of metal rod increases.

Which of the following represents a chemical change?

  1. Rusting of iron.

  2. Magnesium burns in air leaving behind a powdery ash.

  3. Explosion of a firework.

  4. All of the above.


Correct Option: D
Explanation:

All of the following represents a chemical change.

Rusting of iron.
Magnesium burns in air leaving behind a powdery ash.
Explosion of a firework.

In which type of change, alteration takes place only in specific property of matter but not composition?

  1. Chemical change

  2. Physical change

  3. Both physical and chemical change

  4. None of the above


Correct Option: B
When the solid A is added to water, it dissolves with the evolution of heat with the formation of two products B and C. The properties of products B and C are entirely different from those of solid A as well as water. Moreover, products B and C cannot be re-converted into solid A and water. When another solid D is added to water, it dissolves to form a product E which cools down. The product E shows the properties of both, solid D as well as water. Moreover, product E can be converted into solid D and water.
Correct statement(s) is/are:
  1. A chemical change occurs when solid A is dissolved in water

  2. A physical change occurs when solid D is dissolved in water

  3. Metal sodium could behave like solid A

  4. Metal E is a mixture


Correct Option: A

Which of the following is not a physical change?

  1. Tearing paper

  2. Bending an iron rod

  3. Freezing water into ice

  4. None of these


Correct Option: D
Explanation:

No new substances are formed in all these three changes. So these are physical change. 

On heating, the colour of zinc oxide changes from white to yellow. This is a/an:

  1. physical change

  2. chemical change

  3. photochemical change

  4. irreversible change


Correct Option: B
Explanation:

Zinc oxide is a white powder, when heated strongly (above $800^0 C$) it turns yellow, but again becomes white again when cold. The hot zinc oxide absorbs some of the blue wavelengths of light making the reflected light more yellow. The loss of oxygen makes it a reversible chemical change.

In a certain change, colour and the magnetic properties of a substance changed. What reaction might this be?

  1. Chemical combination

  2. Photochemical reaction

  3. Irreversible reaction

  4. Physical change


Correct Option: D
Explanation:

Iron is magnetic at room temperature, but at 770 degrees Celsius iron loses its magnetism. However this change is temporary, hence it is an example of physical change.

and the change in color is a physical change because it is easily reversible without affecting the chemical nature of it.

In the_______ properties of molecules remain same even after the change.

  1. physical change

  2. chemical change

  3. biochemical change

  4. photochemical change


Correct Option: A
Explanation:

In physical change properties of molecules remain the same even after the change. Physical properties like colour, density, volume, mass, boiling point, melting point only have an effect on their physical nature, the chemical nature of the substance remains the same. Physical properties are used to observe and describe matter.

Choose the incorrect statement :

  1. Physical change is reversible

  2. Physical change results in the formation of new substances

  3. Chemical change is permanent

  4. Physical change is accompanied by energy change


Correct Option: B
Explanation:

Physical change does not lead to formation of new substances but only chemical changes can produce new substances.

Changes are of _________ kinds.

  1. three

  2. two

  3. four

  4. five


Correct Option: B
Explanation:

Changes are of two kinds: Physical and chemical changes.
A physical change in a substance does not change what the substance is.
Where as in a chemical change, where there is a chemical reaction, anew substance is formed and energy is either given off or absorbed.

Physical changes require _______ energy than chemical changes.

  1. less

  2. more

  3. equal amount of

  4. very high amount of


Correct Option: A
Explanation:

Physical changes require less energy than chemical energies, as they does not involve in making and breaking of bonds as in the case of chemical bonds, which require a lot of energy.

Dissolving sugar in water is a chemical change. True or false?

  1. True

  2. False


Correct Option: B
Explanation:

Dissolving sugar in water is a physical change because sugar molecules are dispersed within the water, but the individual sugar molecules are unchanged.

What property stays the same during physical and chemical changes?

  1. Density

  2. Shape

  3. Mass

  4. Arrangement of particle


Correct Option: C
Explanation:

Since the law of conservation of mass is valid under all circumstances, hence, mass always remains the same, whether a substance undergoes physical change or chemical change. 

Which of the following is an example of chemical change?

  1. Filling up a balloon with hot air.

  2. Taking a glass of water and freezing it by placing it in the freezer.

  3. A plant collecting sunlight and turning it into food.

  4. Your dog ripping up your homework.


Correct Option: C
Explanation:

A plant collecting sunlight and turning it into food is a photosynthesis reaction which is an example of a photochemical reaction. This is a chemical change. 

What characteristic best describes what happen during a physical change?

  1. Composition changes.

  2. Composition stays the same.

  3. Form stays the same.

  4. Mass is lost.


Correct Option: B
Explanation:
Physical changes are changes affecting the form of a chemical substance, but not its chemical composition. 
Physical changes occur when objects or substances undergo a change that does not change their chemical composition.

Common chemical changes are :

  1. change in temperature

  2. formation of precipitate

  3. formation of bubbles

  4. all of above


Correct Option: D
Explanation:

A change in temperature is characteristic of a chemical change. When the reactants are mixed, the temperature change caused by the reaction is an indicator of a chemical change. 


The formation of a precipitate may be one of the most common signs of a chemical reaction taking place. The formation of bubbles, or rather a gas, is another indicator of a chemical reaction taking place. When bubbles form, a temperature change could also be taking place.

So, the correct option is $D$

Heating of ammonium chloride solution is a:

  1. physical change

  2. chemical change

  3. depends on temperature

  4. can't say


Correct Option: A,B
Explanation:

Solid ammonium chloride vapourizes to form gaseous ammonium chloride. This is a physical change. Ammonium chloride is partially dissociated. This a chemical change. The products ammonia and chlorine recombine to form ammonium chloride. This is also a chemical change.

Burning of candle is a :

  1. physical change

  2. chemical change

  3. both a and b

  4. none of these


Correct Option: C
Explanation:

On burning candle, wax melts which is a physical change. Also, the wax near the flame burns and gives $CO _2$, soot, light and heat which is a chemical change. Hence, burning of candle is a physical as well as chemical change.

Which of the following is a physical change?

  1. Cutting trees

  2. Burning of paper

  3. Breakdown of sugars

  4. All of above


Correct Option: A
Explanation:

Physical change does not involve formation of new products. As cutting of trees do not produce anything it is said to be a physical change.

The difference between a physical reaction and a chemical reaction is :

  1. composotion

  2. size

  3. shape

  4. all of above


Correct Option: A
Explanation:

The difference between a physical reaction and a chemical reaction is composition. In a chemical reaction, there is a change in the composition of the substances. In a physical change, there is a difference in the appearance, smell, or simple display of a sample of matter without a change in composition. 

Physical change include change in :

  1. texture

  2. temperature

  3. formation of bubbles

  4. both a and b


Correct Option: D
Explanation:

The texture of a substance can differ with a physical change. For example, if a piece of wood was sanded, waxed, and polished, it would have a very different texture than it initially had like a rough piece of wood. Although, we cannot see temperature change, unless if a change of state is occurring, so it is a physical change. 


Hence, the correct option is $\text{D}$

All of the following involve a chemical change at a particular temperature except :

  1. the formation of HCl from $H _2$ and $Cl _2$

  2. the color change when NO is exposed to air

  3. the formation of steam from buring $H _2$ and $CO _2$

  4. the solidification of vegetable oil at low temperatures

  5. the odor of $NH _3$ when $NH _4Cl$ is rubbed together with $Ca(OH) _2$ powder.


Correct Option: D
Explanation:

All of the following involve a chemical change at a particular temperature except the solidification of vegetable oil at low temperatures.
It involves physical change. The physical state changes from liquid to solid.

Which statement best describes the difference between the two equations shown below?
Equation I: $H _{2}O _{(l)} \rightarrow H _{2}O _{(g)}$
Equation II: $2H _{2}O _{(l)} \rightarrow 2H _{2(g)} + O _{2(g)}$

  1. Equation I represents a physical change because intermolecular forces are broken during the process, where Equation II presents a chemical change because intramolecular forces are broken.

  2. Equation I represents a physical change because intramolecular forces are broken during the process, whereas in Equation II a chemical change because intermolecular forces are broken.

  3. Equation I represents a chemical change because intermolecular forces are broken, and Equation II represents a physical change because intramolecular forces are broken.

  4. Equation I represents a chemical change because intramolecular forces are broken, and Equation II represents a physical change because intermolecular forces are broken.


Correct Option: A
Explanation:

$(I)$  ${ H } _{ 2 }{ O } _{ \left( l \right)  }\longrightarrow { H } _{ 2 }{ O } _{ \left( g \right)  }$   physical change (reversible)

intermolecular force (Hydrogen bonding) is broken during the process.
$(II)$ $2{ H } _{ 2 }{ O } _{ \left( l \right)  }\longrightarrow 2{ H } _{ 2\left( g \right)  }+{ O } _{ 2\left( g \right)  }$ 
it is a chemical change as it is changing the composition of molecule. Intramolecular forces (Bond breaking) are broken during the process.

All of the following could represent a physical process except:

  1. Formation of a gas

  2. A release of energy from a system into the surroundings

  3. The appearance of substances in two phases of matter at the same time

  4. Appearance of a smell that was no previously present


Correct Option: A
Explanation:

Formation of gas not a physical change because some reactions has taken place which leads to the formation of gas hence, it is a chemical change.

Whereas all the three are physical changes, as they are not producing any new products.

When carbon dioxide is passed through lime water, it turns milky due to the formation of

  1. calcium hydroxide

  2. calcium carbonate

  3. calcium oxide

  4. calcium


Correct Option: B
Explanation:

$Ca{ (OH) } _{ 2 }+C{ O } _{ 2 }\rightarrow CaC{ O } _{ 3 }+{ H } _{ 2 }O$

When carbon dioxide is passed through lime water, it turns milky due to formation of white precipitate in form of calcium carbonate.

Which of the following processes involves a chemical change?

  1. Melting of ice

  2. Photosynthesis

  3. Beating of aluminium sheet to make foil

  4. Melting of wax


Correct Option: B
Explanation:

$(A)$ Melting of ice is reversible, $\therefore $  physical change also no change in chemical composition.

$(B)$ ${ 6CO } _{ 2 }+12{ H } _{ 2 }O\rightarrow { C } _{ 6 }{ H } _{ 12 }{ O } _{ 6 }+{ O } _{ 2 }+{ H } _{ 2 }O$
       (chemical change)
$(C)$ malleability $-$ turning into this sheet $-$ physical change as no change in chemical composition.
$(D)$ similarly wax melting can be reversed.

If pressure is applied to the equilibrium system of solid $ \rightleftharpoons $ liquid, the melting point of the liquid:

  1. will not chabge

  2. may increase or decrease depending upon its nature

  3. will always increase

  4. will always decrease


Correct Option: C
Explanation:
  1. If pressure is applied, according to clausices-ceapeyron equation, the melting point will increase for liquids and decrease for water.
    2. Any external changes that try to take it out of equilibrium will came the system to adjust in a way to counter act that change.

Water on cooling to zero degrees becomes ice. The main reason for this conversion is the hydrogen bonding. Which one of the following statements is correct?

  1. In ice, the hydrogen bonded H atoms are at equal distance from the other two covalently bounded H atoms around each O atom due to resonance

  2. In ice, the hydrogen bonded H atoms are at longer distance as compared to the other two covalently bounded H atoms around each O atom

  3. In ice, the hydrogen bonded H atoms are at shorter distance as compared to the other two covalently bounded H atoms around each O atom

  4. None of these


Correct Option: B
Explanation:

Covalent bonds have higher bond energy (ie, they are strong) compared to Hydrogen bondings.

The higher the bond energy, the shorter is the bond length.
Since bond energy of hydrogen-bonded $H$ atom is lesser than covalently bonded $H$ atom, it is at a longer distance from $O$ atom.
Hence, the correct option is B. 

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