Deuterium oxide, O, and water, O, have the same chemical structure and differ only in that O possesses the deuterium isotope of hydrogen, whereas water possesses the protium isotope. Deuterium oxide, also known as "heavy water," is 11 percent heavier than water. Might you expect its boiling temperature also to be about 11 percent greater? Why or why not?

Question

Deuterium oxide,  O, and water,  O, have the same chemical structure and differ only in that  O possesses the deuterium isotope of hydrogen, whereas water possesses the protium isotope. Deuterium oxide, also known as "heavy water," is 11 percent heavier than water. Might you expect its boiling temperature also to be about 11 percent greater? Why or why not?

Quizplus · Accepted Answer

The boiling temperature of a substance is largely determined by the strength of intermolecular forces (e.g. van der Waals forces, hydrogen bonding) between molecules, which in turn is determined primarily by the nature of the chemical bonds in the molecules and the size and shape of the molecules. Since deuterium oxide and water have the same chemical structure, they should have similar intermolecular forces and thus similar boiling temperatures, regardless of the difference in mass between their molecules. Choice A is incorrect because both mass and polarity influence boiling temperature to some extent, but the influence of polarity is generally weaker than that of mass. Choice C is incorrect because although deuterium is technically radioactive, deuterium oxide itself is not particularly unstable or susceptible to breaking down, and even if it were, this would not necessarily affect its boiling temperature. Choice D is incorrect because boiling temperature is actually a measure of the vapor pressure of a substance, which is in turn related to the average kinetic energy of its molecules. Heavier molecules do not necessarily move more slowly than lighter ones, and even if they did, this would not necessarily result in a higher boiling temperature.

Deuterium Oxide, O, and Water, O, Have the Same