Tag: chemistry

Quizzes (490) Questions (9892)

Questions Related to chemistry

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

When substance cool off, there is a decrease in:

  1. size of substance

  2. vibrations of the molecules

  3. temperature

  4. all of the above
Reveal answer Fill a bubble to check yourself
D Correct answer
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.

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

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

  1. heating

  2. freezing

  3. constant conditions

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

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

Permanent change is a :

  1. Physical change

  2. Chemical 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 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.

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

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

  1. Physical and reversible change.

  2. Chemical and reversible change.

  3. Physical and irreversible change.

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

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

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

Burning of Magnesium ribbon is a _______

  1. Chemical change

  2. Physical change

  3. Reversible change

  4. None of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

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

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 $Ca{C} _{2}$ :

  1. $0.6457kg$
  2. $0.4375kg$
  3. $0.5113kg$
  4. $0.3948kg$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Calcium carbide (CaC2) reacts with water to form acetylene (C2H2). Acetylene is reduced to ethylene (C2H4), which is then polymerized to form polythene (CH2CH2)n. Stoichiometric calculation shows 1 mole of CaC2 produces 1 mole of C2H2, which produces 1 mole of C2H4, resulting in 28g of ethylene units per 64g of CaC2.

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

Examples of slow reaction are:

  1. rusting of iron

  2. weathering of rocks

  3. neutralization of sodium hydroxide by hydrochloric acid

  4. formation of coal
Reveal answer Fill a bubble to check yourself
A,B,D Correct answer
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