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NEET chemistry

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Question
CBSEENCH11008225
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The addition of a catalyst during a chemical reaction alters which of the following quantities ?

  • Internal energy

  • Enthalpy

  • Activation energy

  • Entropy

Solution

C.

Activation energy

A catalyst is a substance which alters the reaction but itself remains unchanged in the chemical reaction. In a chemical reaction, it provides a new reaction path by the lowering the activation energy barrier.

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Question
CBSEENCH11008226
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Predict the correct order among the following.

  • long pair-lone pair> bond pair-bond pair> lone pair>bond pair

  • bond pair-bond pair> lone pair-bond pair > lone pair -lone pair

  • lone pair -bond pair > bond pair- bond pair> lone pair -lone pair

  • lone pair - lone pair > lone pair-bond pair > bond pair -bond pair

Solution

D.

lone pair - lone pair > lone pair-bond pair > bond pair -bond pair

According to the VSPER theory, a lone pair occupies more space than a bond pair, Hence when lone pair-lone pair interacts with each other they repel more and thus the correct order is:
lone pair - lone pair > lone pair-bond pair > bond pair -bond pair.

Question
CBSEENCH11008227
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Two electrons occupying the same orbital are distinguished by

  • Magnetic quantum number

  • Azimuthal quantum number

  • Spin quantum number

  • Principal quantum number

Solution

C.

Spin quantum number

Two electrons occupying the same orbital has equal spin but the directions of their spin are opposite. Hence, spin quantum number, s(represented +1/2 and -1/2) distinguishes them.

Question
CBSEENCH11008228
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The electronic configuration of Eu (Atomic no.63), Gd (Atomic no. 64) and Tb (Atomic no. 65) are

  • [Xe]4f6 5d1 6s2, [Xe] 4f7 5d1 6s2 and [Xe] 4f9  6s2 

  • [Xe] 4f6 5d1 6s2 , [Xe] 4f7 5d1 6s2 and [Xe] 4f8 5d1 6s2 

  • [Xe] 4f7  6s2, [Xe] 4f7 5d1 6s2 and [Xe] 4f9 6s2 

  • [Xe] 4f7  6s2,[Xe] 4f8  6s2 and [Xe] 4f8 5d1 6s2

Solution

C.

[Xe] 4f7  6s2, [Xe] 4f7 5d1 6s2 and [Xe] 4f9 6s2 

Electronic configuration of 63Eu [europium ]
= [Xe] 4f7  6s2, 
Electronic configuration of 64Gd [gadolinium ]
= [Xe] 4f7 5d1 6s2 
Electronic configuration 65Tb [terbium]
= [Xe] 4f9 6s2 

Question
CBSEENCH11008230
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Which one of the following characteristics is associated with adsorption?

  • ΔG, ΔH and  ΔS all are negative

  • ΔG and  ΔH are negative but  ΔS is positive

  • ΔG and  ΔS are negative but  ΔH is positive

  • ΔG is negative but  ΔH and  ΔS are positive

Solution

A.

ΔG, ΔH and  ΔS all are negative

Adsorption is a spontaneous process that occurs with the release of energy and decrease in the entropy of the substance. For a spontaneous process,  ΔG must be  negative,
 ΔG = ΔH - T ΔS
As the process is exothermic and randomness of the molecule (entropy) decreases hence both  ΔH and  ΔS will be negative as well.

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