Question

One reason suggested for the instability of long chains of silicon atoms is that the decomposition involves the transition state shown below: The activation energy for such a process is \(210 \mathrm{~kJ} / \mathrm{mol}\), which is less than either the \(\mathrm{Si}-\mathrm{Si}\) or the \(\mathrm{Si}-\mathrm{H}\) bond energy. Why would a similar mechanism not be expected to play a very important role in the decomposition of long chains of carbon atoms as seen in organic compounds?

Short answer

The decomposition process of long silicon chains occurs relatively easily due to the activation energy of \(210~\mathrm{kJ/mol}\) being lesser than the Si-Si and Si-H bond energies. However, in the case of long carbon chains in organic compounds, the bond energies of C-C (\(347~\mathrm{kJ/mol}\)) and C-H (\(413~\mathrm{kJ/mol}\)) are significantly higher than the activation energy for decomposition of silicon chains. Consequently, carbon chains are much more stable, and the activation energy required for their decomposition would also be higher. This indicates that the decomposition process observed in silicon chains would not play a crucial role in the decomposition of carbon chains in organic compounds.

Step-by-step solution

Understand the decomposition process of silicon chains

The given activation energy of 210 kJ/mol for the decomposition of long chains of silicon atoms is less than the bond energies of Si-Si and Si-H. This means that the decomposition process is relatively easy to happen in such long chains.

Compare activation energy with bond energies in carbon chains

In the case of long chains of carbon atoms in organic compounds, the activation energy for decomposition needs to be compared to the bond energies of C-C and C-H bonds. To understand the mechanism in carbon chains, we have to analyze the bond energies in these compounds. The typical bond energies for C-C and C-H bonds in organic compounds are: C-C bond energy: approximately \(347~\mathrm{kJ/mol}\) C-H bond energy: approximately \(413~\mathrm{kJ/mol}\)

Determine the stability of carbon chains

When comparing the activation energy for decomposition of long carbon chains to the bond energies of the C-C and C-H bonds, we can see that the bond energies are significantly higher than the activation energy for decomposition of silicon chains.

Explain the difference in decomposition mechanisms

The higher bond energies in carbon chains indicate that they are much more stable than silicon chains. Since the activation energy required for decomposition is typically inversely related to the stability of the compounds, it is expected that the activation energy for the decomposition of long chains of carbon atoms in organic compounds would also be higher than the corresponding values for silicon chains. This suggests that the decomposition process observed in silicon chains would not play a very important role in the decomposition of carbon chains.

Key concepts

Understanding Activation Energy

Activation energy is a fundamental concept in chemistry, especially when discussing reaction rates and stability. It represents the minimum amount of energy required for reactants to undergo a chemical transformation. Imagine it as the 'energy hill' that reactants must climb to react and form products. If the activation energy is high, a reaction may proceed slowly or require additional energy input, like heat, to get started.

For instance, when evaluating why silicon chains are less stable than carbon chains, the activation energy is a critical factor. A lower activation energy for the decomposition indicates that it doesn't take much energy for the process to occur. This is why the given activation energy of 210 kJ/mol for silicon chains suggests that these chains can decompose relatively easily.

Decomposition of Silicon Versus Carbon Chains

When comparing the stability of silicon chains to carbon chains, we delve into the realm of decomposition mechanisms. Decomposition is the process by which a compound breaks down into simpler substances or elements. In the context of carbon versus silicon chains, the decomposition involves breaking the bonds between the atoms within the chains.

The discussion brings us to the question of why a similar decomposition mechanism observed in silicon chains isn't prevalent in carbon chains. The simple answer lies in the structure and energy dynamics of the bonds. Carbon chains, ubiquitous in organic chemistry, are known for their robustness due to the strength of the carbon-carbon (C-C) and carbon-hydrogen (C-H) bonds. As per our exercise, it's clear that the bond energies in organic compounds far exceed the activation energy needed to decompose silicon chains, implying a greater stability and resilience of carbon chains against such decomposition processes.

Bond Energies Comparison between Silicon and Carbon Chains

Bond energy is the measure of bond strength in a chemical bond. It's quantified as the amount of energy needed to break the bond and separate atoms in a molecule. Higher bond energies imply a stronger, more stable bond, which correlates with less reactivity and resistance to decomposition.

In the case of silicon chains, the Si-Si and Si-H bond energies are less than those of their carbon counterparts, resulting in a chemical structure more prone to breaking apart. This contrast becomes particularly apparent when looking at the bond energies for C-C and C-H bonds, which are significantly higher at approximately 347 kJ/mol and 413 kJ/mol, respectively, compared to the activation energy for the decomposition of silicon chains. Such a comparison elucidates why carbon chains, such as those found in proteins and DNA, form the backbone of life, withstanding the various chemical reactions that occur within living organisms.