Comparing Pi-Bond Contribution to Enthalpy of C-C & N-N Bonds

In summary, the difference in electronegativity between carbon and nitrogen can explain the difference in pi bond contribution to the enthalpy of C-C and N-N bonds.
  • #1
Julia78
4
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Hi- I have been working on a problem and cannot figure out the last part.
First, I needed to calculate the average pi-bond contribution to the enthalpy for C-C single, double, and triple bonds.
Given: C-C single=348, doube=614, triple=839 kj/mol
I calculated:
839-614=225
614-348=226
So the average is 245.5 kj/mol

Next, I had to make similar comparison for N-N bonds.
Given: N-N single=163; double= 418; triple= 941 kj/mol

Calculations:
941-418=523
418-163=255
So, the average is 389 kj/mol

Now what I am trying to figure out is why there is such a difference in those numbers?
Why pi-bond contribution to bond enthalpy is so much lower in carbon?
Can anybody give me a hint? Does it have to do with numbers of electrons, or orbital configuration?
 
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  • #2
One possible explanation for the difference in the pi bond contribution to the enthalpy of C-C and N-N bonds is the difference in electronegativity between carbon and nitrogen. Carbon has an electronegativity of 2.55 while nitrogen has an electronegativity of 3.04. This difference in electronegativity creates a greater degree of polarity in the N-N bond, which requires more energy to break. This explains why the pi bond contribution to the enthalpy of N-N bonds is higher than that of C-C bonds.
 

1. What is the significance of comparing Pi-Bond Contribution to Enthalpy of C-C & N-N Bonds?

Comparing the Pi-Bond Contribution to Enthalpy of C-C & N-N Bonds allows us to understand the relative strengths of these bonds and how their structure affects their stability.

2. How do the enthalpy values of C-C & N-N bonds compare to each other?

The enthalpy of a C-C bond is typically higher than that of a N-N bond, indicating that the C-C bond is stronger. This is due to the greater electronegativity difference between carbon and hydrogen compared to nitrogen and hydrogen.

3. What role does pi-bonding play in the enthalpy of C-C & N-N bonds?

Pi-bonding, or the sharing of electrons in the p-orbitals of adjacent atoms, contributes significantly to the stability of both C-C and N-N bonds. However, the extent of pi-bonding is greater in C-C bonds, making them stronger.

4. How does the structure of C-C & N-N bonds affect their enthalpy?

The geometry of C-C and N-N bonds can affect the extent of pi-bonding and, therefore, their enthalpy values. For example, a triple bond between two carbon atoms (C≡C) has a greater pi-bond contribution and is therefore stronger than a double bond (C=C). In contrast, a single bond between two nitrogen atoms (N-N) is weaker than a double bond (N=N) due to the repulsion of the lone pairs on both nitrogen atoms.

5. How can the enthalpy of C-C & N-N bonds be experimentally determined?

The enthalpy of a bond can be experimentally determined through techniques such as calorimetry or bond dissociation energy measurements. These methods involve breaking the bond and measuring the energy released or absorbed in the process.

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