Tag: change around us

Questions Related to change around us

Which of the following is correctly matched?

chemistry change around us physical changes changes and their classification physical changes

  1. Making of ice cube - Physical Change.

  2. Folding of a paper - Chemical, Reversible.

  3. Breaking of a glass - Chemical, Irreversible.

  4. All of these

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Correct Option: A

Cutting of a log of wood is a chemical change.

chemistry change around us physical changes changes and their classification physical changes

  1. True

  2. False

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Correct Option: B
Explanation:

False

The cutting of wood piece is a physical change. Cutting would give rise to a new wood piece in which no new substance is formed so its a physical change. 

Two changes are stated below:
(i.) A piece of magnesium gives of bright flames when burned.
(ii). A piece of iron glows red when heated strongly.
 Which of these is a physical change?

chemistry change around us physical changes changes and their classification physical changes

  1. Only i

  2. Only ii

  3. Both i and ii

  4. Neither i nor ii

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Correct Option: B
Explanation:

When magnesium is burnt, it reacts with the heat and gives bright flames and this change cannot be reversed.
When iron heated strongly it turns red. When heating is stopped it cools and get backs to its original form. So this is a physical change.

Dissolving salt in water-is a/an:

chemistry change around us physical changes changes and their classification physical changes

  1. endothermic change

  2. exothermic change

  3. both A& B

  4. chemical combination

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Correct Option: A
Explanation:

When salt (solid crystal) is dissolved in water energy is required to break the intermolecular attraction between ions (Lattice energy). Hence the energy is collected from water which leads to a decrease in its temperature.

Hence endothermic reaction.

Adding sodium chloride to water is a:

chemistry change around us physical changes changes and their classification physical changes

  1. physical change

  2. chemical change

  3. chemical reaction

  4. none of these

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Correct Option: A
Explanation:

Adding sodium chloride to water is a physical change as the sodium chloride can be separated from water by evaporation.

Pooja took a candle in a vessel and heated the vessel. Even though the candle did not burn, it changed its shape and state. What kind of change is this?

chemistry change around us physical changes changes and their classification physical changes

  1. Naturalization

  2. Physical change

  3. Chemical change

  4. None of these

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Correct Option: B
Explanation:

Candle is made up of wax which melts on heating.When candle kept in a vessel and heated, the wax melts. When candle is allowed to cool, the wax solidifies. No new substance is formed. So, this is a physical change.

In a physical change :

chemistry change around us physical changes changes and their classification physical changes

  1. new substances are not formed

  2. reaction is reversible

  3. change is temporary

  4. All of the above

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Correct Option: D
Explanation:

Physical changes in a substance do not form new substances, these reactions are reversible and the change is temporary.

Physical changes are the changes affecting the form of a chemical substance, but not its chemical composition. They are used to separate mixtures into their component compounds, but cannot usually be used to separate compounds into chemical elements or simpler compounds.

Identify the substance that evaporates at room temperature.

chemistry change around us physical changes changes and their classification physical changes

  1. Water

  2. Oil

  3. Kerosene

  4. Ammonium chloride

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Correct Option: C

In early winter mornings, we can see drops of water on the blades of grass. This is because of :

chemistry change around us physical changes changes and their classification physical changes

  1. photosynthesis

  2. transpiration

  3. condensation

  4. water cycle

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Correct Option: C
Explanation:

Dew drops are formed due to condensation of water vapors. The air around us contains water vapors which we call moisture or humidity. Hot air contains more moisture as compared to cold air. During the night when the hot air comes into contact with some cold surface, water vapor present in it condenses on the cold surface in the form of droplets. These tiny drops of water are called dew drops.

Dissolution of carbon dioxide gas in water is  ________ change.

chemistry change around us physical changes changes and their classification physical changes

  1. chemical

  2. physical

  3. both of $A$ and $B$

  4. none of the above

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Correct Option: C
Explanation:

Dissolution of carbon dioxide gas in water is both a physical and chemical change.
Carbon dioxide dissolves in water producing carbonic acid, also known as soda water.
$ CO _2 + H _2O\rightarrow H _2CO _3$
There will be an equilibrium constant that will dictate the relative concentration of dissolved gas to the corresponding acid that is formed.
Usually nonmetal oxides like$CO _2, SO _2, NO _2$  simply dissolve in water, depending on the partial pressure above the water, and Henrys law constant. This implies a physical change.