Question

Why do we not consider the basic strength and consider bond enthalpy while taking the order of reducing character in hydrides of N family?

Answer 1

When determining the reducing character of hydrides in the nitrogen family (Group 15), we prioritize bond enthalpy over basic strength because bond enthalpy is a more accurate representation of the energy required to break the bond between the element and hydrogen. The bond enthalpy reflects the strength of the bond and the energy required to remove the hydrogen atom.

In the context of reducing character, a stronger reducing agent is one that more readily donates electrons or removes hydrogen atoms. A hydride with a lower bond enthalpy requires less energy to break the bond and release hydrogen, making it a stronger reducing agent.

While basic strength can indicate the availability of electrons, it does not directly correlate with the reducing character of hydrides. Basic strength is more relevant when considering proton acceptability in acid-base reactions.

Therefore, in the case of Group 15 hydrides (such as NH3, PH3, AsH3, and SbH3), bond enthalpy is considered the more appropriate factor to analyze reducing character, as it gives a clearer picture of the energy required for the hydride to act as a reducing agent.

Answer 2

The order of reducing character in hydrides of the nitrogen family (Group 15) is often determined primarily based on bond enthalpies rather than basic strength due to several reasons:

1. Bond Enthalpy Reflects Bond Strength: Bond enthalpy refers to the energy required to break a chemical bond. In the case of hydrides, the strength of the M-H bond (where M represents the element from the nitrogen family) plays a crucial role in determining reducing character. Hydrides with weaker M-H bonds tend to be better reducing agents because they can more readily donate hydrogen atoms. Therefore, comparing bond enthalpies provides valuable information about the strength of the M-H bonds and hence the reducing ability of the hydrides.

2. Multiple Factors Determine Basic Strength: Basic strength refers to the ability of a compound to donate a pair of electrons. While basic strength is an important factor in certain chemical reactions, it may not fully capture the reactivity of hydrides in terms of reducing ability. Other factors such as bond strength, bond polarity, and steric effects also influence the reactivity of hydrides. Bond enthalpy accounts for the strength of the M-H bond, which is crucial in determining the reducing character of hydrides.

3. Consistency in Comparison: Bond enthalpies provide a quantitative measure that allows for a consistent comparison of the strength of M-H bonds across different hydrides within the nitrogen family. This consistency aids in determining the order of reducing character among hydrides based on their relative bond strengths.

In summary, while basic strength is an important property in certain contexts, bond enthalpy is often preferred for determining the order of reducing character in hydrides of the nitrogen family due to its direct reflection of bond strength, which is a key factor influencing the reactivity of hydrides as reducing agents.