Tag: chemistry

Questions Related to chemistry

When substance cool off, there is a decrease in:

chemistry phenomena around us changes and its classification types of changes classification of changes

  1. size of substance

  2. vibrations of the molecules

  3. temperature

  4. all of the above

Show answer
Correct Option: D
Explanation:

When a substance cools off, the size of substance, vibrations, a temperature of the substance decreases, as the heat is dissipated out resulting in the decrease in the size of the substance, and the internal vibrations between the molecules also decrease as the temperature decreases, due to the loss of heat.

A metal ball which is passing through metal ring will not pass after :

chemistry phenomena around us changes and its classification types of changes classification of changes

  1. heating

  2. freezing

  3. constant conditions

  4. refrigerating

Show answer
Correct Option: A
Explanation:

All metals have a property of expansion when heated. Since the metal ball is heated, it will expand and will not pass the ring now.


Thus heating is the correct answer.

Hence the option A is correct.

Things or processes which cannot be reversed are called

chemistry phenomena around us changes and its classification types of changes classification of changes

  1. Irreversible process

  2. Reversible process

  3. Cyclic process

  4. None of the above

Show answer
Correct Option: A
Explanation:

Things or processes which cannot be reversed are called irreversible process Burning of coal is irreversible as it will not produce coal again.

Which of the following processes prevents iron from rust?

chemistry phenomena around us changes and its classification types of changes classification of changes

  1. Galvanization

  2. Painting

  3. Both a and b

  4. None of the above

Show answer
Correct Option: C
Explanation:

Galvanization(Coating of non-reactive metal on iron) and painting prevents iron to get in contact with moisture thus prevent it from rusting. 


Hence, option C is correct.

Permanent change is a :

chemistry phenomena around us changes and its classification types of changes classification of changes

  1. Physical change

  2. Chemical change

  3. Both physical and chemical change

  4. None of the above

Show answer
Correct Option: B
Explanation:

A chemical change is permanent. A new substance is formed.


Forms of energy, such as heat, light or electricity, may be emitted or absorbed during a chemical reaction. A chemical change is generally irreversible.

Hence option B is correct.

Change of water into vapor (Vaporization) is which of the following change

chemistry phenomena around us changes and its classification types of changes classification of changes

  1. Physical and reversible change.

  2. Chemical and reversible change.

  3. Physical and irreversible change.

  4. Irreversible change

Show answer
Correct Option: A
Explanation:

Vapor is another physical state of water. Water can be obtained from the  condensation of vapor. This is a physical and reversible change.

Burning of Magnesium ribbon is a _______

chemistry phenomena around us changes and its classification types of changes classification of changes

  1. Chemical change

  2. Physical change

  3. Reversible change

  4. None of the above

Show answer
Correct Option: A
Explanation:

Magnesium ribbon burns with dazzling light in air and forms magnesium oxide.
$2Mg+O _2\rightarrow 2MgO$.
The above change is a chemical changes as new substance is  formed after change. Original
substances cannot be retrieved by simple physical processes.So it is chemical change.
Hence option A is correct.

Things or processes which can be reversed are called

chemistry phenomena around us changes and its classification types of changes classification of changes

  1. Reversible process

  2. Irreversible process

  3. Cyclic process

  4. None of the above

Show answer
Correct Option: A
Explanation:

Things or processes which can be reversed are called reversible. For example, ice melts into water and water freeze into ice which is reversible. Hence, option A is correct.

Calcium carbide produces acetylene on reaction with water. Ethylene can be obtained by reduction of ${C} _{2}{H} _{2}$. Polythene is produced by polymerization of ${C} _{2}{H} _{4}$. Calculate the theoretical yield of polythene per kilogram of $Ca{C} _{2}$ :

chemistry phenomena around us changes and its classification types of changes classification of changes

  1. $0.6457kg$

  2. $0.4375kg$

  3. $0.5113kg$

  4. $0.3948kg$

Show answer
Correct Option: B

Examples of slow reaction are:

chemistry phenomena around us changes and its classification types of changes classification of changes

  1. rusting of iron

  2. weathering of rocks

  3. neutralization of sodium hydroxide by hydrochloric acid

  4. formation of coal

Show answer
Correct Option: A,B,D
Explanation:
Reactions that take a while are slow reactions and those which occur within a few seconds are fast reactions. The rusting of iron, the fermentation of sugar into alcohol, the chemical weathering of rocks (breaking down of rocks), the photosynthesis process in plants, coal formation are slow reactions. Whereas neutralization reaction of a strong base like sodium hydroxide and strong acid like $HCl$ is a fast reaction.
option A,B,D are correct