Final answer:
The phrase 'Four molecules of Water' or 'Four molecules of dihydrogen monoxide' refers to the same substance, which is water (H2O). Water is a compound containing two hydrogen atoms bonded to one oxygen atom, with the oxygen having four electron groups, of which only two are bonded to hydrogens. Chemical reactions such as the combustion of ethane show how molecules and moles are used to express quantities in chemistry.
Step-by-step explanation:
The question whether referring to 'Four molecules of Water' or 'Four molecules of dihydrogen monoxide' essentially talks about the same chemical substance, which is water (H₂O). In chemistry, dihydrogen monoxide is a less common but still accurate name for water. When talking about the molecular structure, H₂O consists of two hydrogen atoms covalently bonded to a single oxygen atom. The central oxygen atom in a water molecule has four electron groups, but only two of these groups are used for bonding with the hydrogen atoms; the other two groups are lone pairs of electrons.
An example to illustrate the concept of molecules and moles can be seen in chemical reactions, such as the combustion of ethane (C₂H₆) where two moles of C₂H₆ react with seven moles of O₂ to yield four moles of CO₂ and six moles of H₂O. This demonstrates the stoichiometry of a chemical reaction where ratios of reactants and products are based on mole quantities. Lastly, it is important to clarify that changing the subscript in a chemical formula, such as turning H₂O into H₂O₂, would result in a completely different compound, which is hydrogen peroxide in this case.