When the enthalpy of this overall chemical equation is calculated, the enthalpy of the second intermediate equation is halved and has its sign changed.
is halved.
has its sign changed.
is unchanged.

The correct answer is " is halved and has its sign changed".

Explanation:

I had to find the chemical equation that the statement refers to.

When the enthalpy of this overall chemical equation is calculated, the enthalpy of the second intermediate equation is halved and its sign changes. This is because in the global equation only one CaO molecule is used, while in the semi-reaction the enthalpy change for two CaO molecules is given, so the enthalpy change must be divided by 2. Also, the sign changes because in the globular equation the inverse reaction of the one shown in the semi-reaction is produced, in this way we have that the CaO is on the side of the reagents and in the semi-reaction it is on the side of the products.

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vanderwaal's forces of attraction are the electrostatic intermolecular forces that exist in a molecule due to the temporary or permanent dipoles that are developed in a molecule. in , the major intermolecular forces are dipole-dipole interactions as the molecule is polar (bent structure). so the vanderwaal's forces of interaction in between molecules are the permanent dipole-dipole interactions that develop due to the dipole that exists in between the polar h - s bond. the positively charged hydrogen atom is attracted towards the negative end of the dipole that is sulfur of the adjacent molecule. therefore, these forces of attraction are relatively stronger than that of london dispersion forces that exist in non polar molecules.