Question 36

Arrange the following in the order of property indicated for each set:

(i) F₂, Cl₂, Br₂, I₂- increasing bond dissociation enthalpy.

(ii) HF, HCl, HBr, HI - increasing acid strength.

(iii) NH₃, PH₃, AsH₃, SbH₃, BiH₃- increasing base strength.

Answer

(i) Bond dissociation energy usually decreases on moving down a group as the atomic size increases. However, the bond dissociation energy of F2 is lower than that of Cl₂ and Br₂. This is due to the small atomic size of fluorine. Thus, the increasing order for bond dissociation energy among halogens is as follows:

I₂< F₂< Br₂< Cl₂

(ii) HF < HCl < HBr < HI

The bond dissociation energy of H-X molecules where X = F, Cl, Br, I, decreases with an increase in the atomic size. Since H-I bond is the weakest, HI is the strongest acid.

(iii) BiH₃ < SbH₃ < AsH₃ < PH₃ < NH₃

On moving from nitrogen to bismuth, the size of the atom increases while the electron density on the atom decreases. Thus, the basic strength decreases.

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Arrange the following in the order of property indicated for each set:

(i) F₂, Cl₂, Br₂, I₂- increasing bond dissociation enthalpy.

(ii) HF, HCl, HBr, HI - increasing acid strength.

(iii) NH₃, PH₃, AsH₃, SbH₃, BiH₃- increasing base strength.

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Arrange the following in the order of property indicated for each set: (i) F2, Cl2, Br2, I2- increasing bond dissociation enthalpy. (ii) HF, HCl, HBr, HI - increasing acid strength. (iii) NH3, PH3, AsH3, SbH3, BiH3- increasing base strength.

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