Why Are Bond Enthalpies Restricted to Gaseous State?

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In summary, bond enthalpy, also known as bond energy, is the amount of energy required to break a chemical bond between two atoms in a molecule. This measurement is restricted to the gaseous state due to the lack of intermolecular interactions, and can vary between different molecules depending on the types and strength of bonds present. Higher bond enthalpies indicate stronger bonds and a more stable molecule. In chemical reactions, bond enthalpies determine the energy required to break bonds and form new ones, driving the reaction forward.
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Cheman
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Bond enthalpies...

Apparently from what I have read, mean bond enthalpies are only given for things in gaseous state - why is this the case? Why can we not quote bond enthalpies in, say, the solid or liquid state?

Thanks. :-D
 
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It is difficult to experimentally determine the bond enthalpies in the solid or liquid state; usually because it takes less energy to melt/boil the substance than it takes to break all bonds between specific atoms.
 
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Bond enthalpies are restricted to the gaseous state because the calculation of bond enthalpies involves the breaking and forming of bonds, which can only occur in the gas phase. In solids and liquids, the molecules are closely packed together and have strong intermolecular forces, making it difficult for individual bonds to be broken or formed without affecting the entire structure. In the gas phase, however, molecules are more spread out and have weaker intermolecular forces, allowing for easier breaking and forming of bonds. Therefore, bond enthalpies can only be accurately measured and calculated in the gaseous state. Additionally, the bond enthalpy values for different compounds may vary depending on the physical state, so it is important to specify that the values given are for the gaseous state.
 

1. What is bond enthalpy?

Bond enthalpy, also known as bond energy, is the amount of energy required to break a chemical bond between two atoms in a molecule.

2. Why are bond enthalpies restricted to the gaseous state?

Bond enthalpies are restricted to the gaseous state because the molecules in a gaseous state are more spread out and have less intermolecular interactions, allowing for a more accurate measurement of the energy required to break a specific bond.

3. How do bond enthalpies vary between different molecules?

The bond enthalpy between two atoms can vary depending on the types of atoms involved and the type of bond (single, double, or triple) between them. Different molecules can also have different bond enthalpies due to the varying strength of the bonds present.

4. Can bond enthalpies be used to predict the stability of a molecule?

Yes, the higher the bond enthalpy, the stronger the bond between two atoms, resulting in a more stable molecule.

5. How do bond enthalpies relate to chemical reactions?

Bond enthalpies play a crucial role in chemical reactions as they determine the amount of energy required to break bonds in reactant molecules and form new bonds in product molecules. This energy difference is what drives the reaction forward.

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