Tag: introduction to physical and chemical changes

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

Identify the physical change:

  1. Photosynthesis

  2. Respiration

  3. Digestion of food

  4. Melting of Wax
Reveal answer Fill a bubble to check yourself
D Correct answer
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.

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

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.
Reveal answer Fill a bubble to check yourself
D Correct answer
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.

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

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
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A physical change affects only the physical properties (like state or shape) of matter, while the chemical composition remains unchanged.

Multiple choice chemistry phenomena around us comparison between physical and chemical changes introduction to physical and chemical changes change around us
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
Reveal answer Fill a bubble to check yourself
A Correct answer
Multiple choice chemistry phenomena around us comparison between physical and chemical changes introduction to physical and chemical changes change around us

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
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

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

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
Reveal answer Fill a bubble to check yourself
D Correct answer
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.

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

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

  1. physical change

  2. chemical change

  3. biochemical change

  4. photochemical change
Reveal answer Fill a bubble to check yourself
A Correct answer
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.