Page 1 of 1

Question 9.29

Posted: Thu Jan 26, 2017 6:12 pm
by Kevin Bangi 1A
List the following substances in order of increasing molar entropy at 298 K: H2O(l), H2O(g), H2O(s), C(s,diamond).

How am i supposed to figure out the molar entropy?
Would i use the equation with the boltzman constant or the Change of entropy equation?

Re: Question 9.29

Posted: Thu Jan 26, 2017 10:43 pm
by Omer Lavian 2K
This question is more conceptual than it is mathematical. If you think back to the equation with Boltzmann's constant, S = KblnW, you see that the entropy depends on W, the number of possible states (often called microstates) in which a material (an atom, a molecule, a substance, etc.) can exist. Think of microstates as the various ways in which the material can arrange itself atomically, molecularly, electronically, and more. When you look at solid water, liquid water, and gaseous water, you know that the molecules of water in the gas phase are more free to move and can thus arrange themselves in more different ways than those in liquid water and those in solid water. So, of the four materials, gaseous water has the most molar entropy, followed by liquid and solid water for the same reason. The real question is whether solid water or diamond has more entropy. To answer that, consider that solid water's molecules are held together by hydrogen bonds, while the carbon atoms in diamonds are all connected by covalent bonds (Materials held together in this way are called network solids.). Therefore, since covalent bonds are stronger than hydrogen bonds, the ice is more free to rearrange itself into various other microstates, meaning that diamond has the least molar entropy of the four materials. Hope that answers your question!