Tag: phenomena around us

Questions Related to phenomena around us

Which of the following represents a chemical change?

chemistry phenomena around us comparison between physical and chemical changes introduction to physical and chemical changes change around us

  1. Rusting of iron.

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

  3. Explosion of a firework.

  4. All of the above.

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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?

chemistry phenomena around us comparison between physical and chemical changes introduction to physical and chemical changes change around us

  1. Chemical change

  2. Physical change

  3. Both physical and chemical change

  4. None of the above

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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:
chemistry phenomena around us comparison between physical and chemical changes introduction to physical and chemical changes change around us

  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

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Correct Option: A

Which of the following is not a physical change?

chemistry phenomena around us comparison between physical and chemical changes introduction to physical and chemical changes change around us

  1. Tearing paper

  2. Bending an iron rod

  3. Freezing water into ice

  4. None of these

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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:

chemistry phenomena around us comparison between physical and chemical changes introduction to physical and chemical changes change around us

  1. physical change

  2. chemical change

  3. photochemical change

  4. irreversible change

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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?

chemistry phenomena around us comparison between physical and chemical changes introduction to physical and chemical changes change around us

  1. Chemical combination

  2. Photochemical reaction

  3. Irreversible reaction

  4. Physical change

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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.

chemistry phenomena around us comparison between physical and chemical changes introduction to physical and chemical changes change around us

  1. physical change

  2. chemical change

  3. biochemical change

  4. photochemical change

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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 :

chemistry phenomena around us comparison between physical and chemical changes introduction to physical and chemical changes change around us

  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

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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.

chemistry phenomena around us comparison between physical and chemical changes introduction to physical and chemical changes change around us

  1. three

  2. two

  3. four

  4. five

Show answer
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.

chemistry phenomena around us comparison between physical and chemical changes introduction to physical and chemical changes change around us

  1. less

  2. more

  3. equal amount of

  4. very high amount of

Show answer
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.