Tag: classification of changes

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

Which of the following is a chemical change

  1. Burning of coal

  2. Dissolving sugar in water

  3. Dissolving salt in water

  4. Melting of ice
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A chemical change is the process in which chemical composition of the substance is changed,and physical composition may or may not changed burning of coal that is carbon(C) in presence of oxygen gives a different chemical substance $CO _2$. So, it is a chemical change. Hence option A is correct.

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

Melting of wax is

  1. Reversible change

  2. Irreversible change

  3. Both A,B

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

In melting of wax, only the physical state of the wax changes from solid to liquid. Solid wax can be obtained from molten wax. Molten wax can be again converted to solid wax. This is an example of physical and reversible change. Hence, option A is correct.

Multiple choice chemistry changes around us can all changes be reversed? substances and objects classification of changes

 Heat gain makes ice to:

  1. freeze

  2. evaporate

  3. melt

  4. dissolve
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

When heat flows through the ice, the ice will melt. 

The liquid has more energy than the solid, mainly because the molecular bonds in the solid adjust to low-energy positions. So energy, when flowed in, will convert the solid to the liquid.
Freezing will happen if the there is heat loss to ice.
Evaporation will happen if the heat gain is very high that makes the ice to convert to water vapor.
The correct answer is option $ C$.

Multiple choice chemistry changes around us can all changes be reversed? substances and objects classification of changes

In the tools which are used to dig the soil, the iron blade in these tools fixed to the wooden handle. Which of the following is used during the change?

  1. Expansion

  2. Contraction

  3. Both expansion and contraction.

  4. Neither expansion and contraction.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Both expansion and contraction is used during the change.
The iron blade has a ring in which the wooden handle is fixed. The ring is slightly smaller in size than the wooden handle.The ring is heated and it becomes slightly larger in size (expands). The handle  fits into the ring. When the ring cools it contracts and tightly fits on the handle.