Which of the following relationships is not correct ?

Options

A. `DeltaH=DeltaU+Deltan_(g)RT`
B. `DeltaH_("sub")=DeltaH_("fusion")+DeltaH_("vap")`
C. `DeltaH_(r)^(@)=SigmaH_(f"(reactants)")^(@)-Sigma_(f"(products)")^(@)`
D. `DeltaH_(r)^(@)=Sigma"B.E. of reactants "-Sigma "B.E. of products"`

Answer

To determine which of the given relationships is not correct, we will analyze each statement one by one.

1. **First Relationship:**
\[ \Delta H = \Delta U + \Delta N_g RT \]
- This relationship is known as the enthalpy change equation, where \(\Delta H\) is the change in enthalpy, \(\Delta U\) is the change in internal energy, \(\Delta N_g\) is the change in the number of moles of gas, and \(R\) is the universal gas constant. This equation is correct.

2. **Second Relationship:**
\[ \Delta H_{\text{sublimation}} = \Delta H_{\text{fusion}} + \Delta H_{\text{vaporization}} \]
- This relationship states that the enthalpy of sublimation (the energy required to convert a solid directly into a gas) is equal to the sum of the enthalpy of fusion (the energy required to convert a solid into a liquid) and the enthalpy of vaporization (the energy required to convert a liquid into a gas). This relationship is also correct.

3. **Third Relationship:**
\[ \Delta H_{\text{formation}} = \Sigma \Delta H_{\text{formation of reactants}} - \Sigma \Delta H_{\text{formation of products}} \]
- This statement is incorrect. The correct relationship for the change in enthalpy of a reaction is given by:
\[ \Delta H_{\text{reaction}} = \Sigma \Delta H_{\text{formation of products}} - \Sigma \Delta H_{\text{formation of reactants}} \]
- The error in the original statement is the order of the terms; it incorrectly places the reactants before the products.

4. **Fourth Relationship:**
\[ \Delta H_{\text{reaction}} = \text{Bond energy of reactants} - \text{Bond energy of products} \]
- This relationship is also correct. It describes the change in enthalpy in terms of bond energies, where the energy required to break bonds in the reactants is subtracted from the energy released in forming bonds in the products.

**Conclusion:**
The relationship that is not correct is the third one:
\[ \Delta H_{\text{formation}} = \Sigma \Delta H_{\text{formation of reactants}} - \Sigma \Delta H_{\text{formation of products}} \]

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