why does the enthalpy of formation for the ethanol dimer have more energy than two isolated ethanol molecules?

is it because there is a bond between the hydrogen of ethanol dimer

Yes, that is one of the reasons why the enthalpy of formation for the ethanol dimer is higher than that of two isolated ethanol molecules. Let me explain further.

Enthalpy of formation is the energy associated with the formation of a compound from its constituent elements. In the case of the ethanol dimer, it is formed by joining two ethanol molecules together through a hydrogen bond. This hydrogen bond is a relatively strong intermolecular force that occurs when a hydrogen atom with a partial positive charge interacts with an electronegative atom, such as oxygen or nitrogen.

When the hydrogen of one ethanol molecule interacts with the oxygen of the other ethanol molecule to form a hydrogen bond in the dimer, it results in a more stable arrangement. This hydrogen bond contributes to a decrease in potential energy, leading to an increase in enthalpy of formation.

Additionally, the formation of the ethanol dimer involves a decrease in entropy. Entropy is a measure of the disorder or randomness in a system. When two ethanol molecules come together to form a dimer, there is a reduction in the number of possible arrangements, which leads to a decrease in entropy. This decrease in entropy also contributes to the higher enthalpy of formation of the ethanol dimer compared to two isolated ethanol molecules.

Therefore, the presence of the hydrogen bond and the decrease in entropy are the main reasons why the enthalpy of formation for the ethanol dimer is higher than that of two isolated ethanol molecules.