Tag: phenomena around us

Questions Related to phenomena around us

All of the following involve a chemical change at a particular temperature except :

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

  1. the formation of HCl from $H _2$ and $Cl _2$

  2. the color change when NO is exposed to air

  3. the formation of steam from buring $H _2$ and $CO _2$

  4. the solidification of vegetable oil at low temperatures

  5. the odor of $NH _3$ when $NH _4Cl$ is rubbed together with $Ca(OH) _2$ powder.

Show answer
Correct Option: D
Explanation:

All of the following involve a chemical change at a particular temperature except the solidification of vegetable oil at low temperatures.
It involves physical change. The physical state changes from liquid to solid.

Which statement best describes the difference between the two equations shown below?
Equation I: $H _{2}O _{(l)} \rightarrow H _{2}O _{(g)}$
Equation II: $2H _{2}O _{(l)} \rightarrow 2H _{2(g)} + O _{2(g)}$

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

  1. Equation I represents a physical change because intermolecular forces are broken during the process, where Equation II presents a chemical change because intramolecular forces are broken.

  2. Equation I represents a physical change because intramolecular forces are broken during the process, whereas in Equation II a chemical change because intermolecular forces are broken.

  3. Equation I represents a chemical change because intermolecular forces are broken, and Equation II represents a physical change because intramolecular forces are broken.

  4. Equation I represents a chemical change because intramolecular forces are broken, and Equation II represents a physical change because intermolecular forces are broken.

Show answer
Correct Option: A
Explanation:

$(I)$  ${ H } _{ 2 }{ O } _{ \left( l \right)  }\longrightarrow { H } _{ 2 }{ O } _{ \left( g \right)  }$   physical change (reversible)

intermolecular force (Hydrogen bonding) is broken during the process.
$(II)$ $2{ H } _{ 2 }{ O } _{ \left( l \right)  }\longrightarrow 2{ H } _{ 2\left( g \right)  }+{ O } _{ 2\left( g \right)  }$ 
it is a chemical change as it is changing the composition of molecule. Intramolecular forces (Bond breaking) are broken during the process.

All of the following could represent a physical process except:

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

  1. Formation of a gas

  2. A release of energy from a system into the surroundings

  3. The appearance of substances in two phases of matter at the same time

  4. Appearance of a smell that was no previously present

Show answer
Correct Option: A
Explanation:

Formation of gas not a physical change because some reactions has taken place which leads to the formation of gas hence, it is a chemical change.

Whereas all the three are physical changes, as they are not producing any new products.

When carbon dioxide is passed through lime water, it turns milky due to the formation of

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

  1. calcium hydroxide

  2. calcium carbonate

  3. calcium oxide

  4. calcium

Show answer
Correct Option: B
Explanation:

$Ca{ (OH) } _{ 2 }+C{ O } _{ 2 }\rightarrow CaC{ O } _{ 3 }+{ H } _{ 2 }O$

When carbon dioxide is passed through lime water, it turns milky due to formation of white precipitate in form of calcium carbonate.

Which of the following processes involves a chemical change?

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

  1. Melting of ice

  2. Photosynthesis

  3. Beating of aluminium sheet to make foil

  4. Melting of wax

Show answer
Correct Option: B
Explanation:

$(A)$ Melting of ice is reversible, $\therefore $  physical change also no change in chemical composition.

$(B)$ ${ 6CO } _{ 2 }+12{ H } _{ 2 }O\rightarrow { C } _{ 6 }{ H } _{ 12 }{ O } _{ 6 }+{ O } _{ 2 }+{ H } _{ 2 }O$
       (chemical change)
$(C)$ malleability $-$ turning into this sheet $-$ physical change as no change in chemical composition.
$(D)$ similarly wax melting can be reversed.

If pressure is applied to the equilibrium system of solid $ \rightleftharpoons $ liquid, the melting point of the liquid:

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

  1. will not chabge

  2. may increase or decrease depending upon its nature

  3. will always increase

  4. will always decrease

Show answer
Correct Option: C
Explanation:
  1. If pressure is applied, according to clausices-ceapeyron equation, the melting point will increase for liquids and decrease for water.
    2. Any external changes that try to take it out of equilibrium will came the system to adjust in a way to counter act that change.

Water on cooling to zero degrees becomes ice. The main reason for this conversion is the hydrogen bonding. Which one of the following statements is correct?

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

  1. In ice, the hydrogen bonded H atoms are at equal distance from the other two covalently bounded H atoms around each O atom due to resonance

  2. In ice, the hydrogen bonded H atoms are at longer distance as compared to the other two covalently bounded H atoms around each O atom

  3. In ice, the hydrogen bonded H atoms are at shorter distance as compared to the other two covalently bounded H atoms around each O atom

  4. None of these

Show answer
Correct Option: B
Explanation:

Covalent bonds have higher bond energy (ie, they are strong) compared to Hydrogen bondings.

The higher the bond energy, the shorter is the bond length.
Since bond energy of hydrogen-bonded $H$ atom is lesser than covalently bonded $H$ atom, it is at a longer distance from $O$ atom.
Hence, the correct option is B.