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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: mindmaze on May 24, 2009, 04:44:33 PM

Title: Conceptual question about energy states and volume of gas (energy spreading)
Post by: mindmaze on May 24, 2009, 04:44:33 PM

Greetings,
After reading about energy states of molecules, I am having difficulty grasping the reasoning behind one phenomenon, namely: "The larger the volume available to the gas, the greater the number of energy states (and thus microstates) its thermal energy can occupy." (taken from http://www.chem1.com/acad/webtext/thermeq/TE1.html#SEC3)

Intuitively, it appears to me that increasing the volume of a gas decreases the average velocities of its molecules (this is also stated in the ideal gas law when the pressure is constant as far as I can tell). Does this not mean that a given molecule can occupy _fewer_ translational energy states?  Could somebody please point out the flaw in my reasoning.

Thank you,
Igor

Title: Re: Conceptual question about energy states and volume of gas (energy spreading)
Post by: leve on May 24, 2009, 10:48:58 PM

Microstates is like entropy. The greater the number of energy states (and thus microstates), the greater the entropy. Entropy is increased at larger volumes and lower pressures.

The way I learned it was that microstates meant all the different places atoms can be in at a given volume. So 1 mol of gas at 2L has more microstates than at 2L because there is more space.