Articles Posted in April 2013 (previously hosted on Blogger) 
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The MaxwellBoltzmann Distribution
The following post was first posted on Blogger on Friday, 5 April 2013. Molecules in a gas sample do not all have the same energy. Rather, there is a distribution of energies. The MaxwellBoltzmann distribution is a graph of the number of molecules with a given amount of energy against that amount of energy. It shows the distribution of molecular energies in a gas sample, and this is what it looks like at different temperatures:
Although it looks like an easy graph to draw, I often find students making silly mistakes. I suspect these came about because they were learning the graph by rote, without fully understanding what it represents.
Common mistake #1: The graph does not begin at the origin.
Common mistake #2: The axis labels are switched.
To help my students better understand the MaxwellBoltzmann distribution, I decided to take them down memory lane, back to their time in primary school when they were learning about bar graphs.
I began with a very, very, very tiny gas sample comprising of just 29 molecules, and assigned a certain amount of energy to each of them such that
Total number of molecules = 3 + 5 + 6 + 5 + 4 + 3 + 2 + 1 = 29
At this point, it became very clear that if this system were to be scaled up to one that contained a very huge number of molecules, one would arrive at the smooth MaxwellBoltzmann distribution curve. And the area under the curve is the total number of molecules in the system.
(There was this look of realisation dawning on my students when I related the simple bar graph to the MaxwellBoltzmann distribution. Let's just hope that I don't see them making the same mistakes again.) 
Chemical Equilibria
The following post was first posted on Blogger on Friday, 26 April 2013.
I should have posted these slides before Ionic Equilibria. My bad.
(To view an expandable version, click here to open slides on SlideShare.)
Update (15 Aug 2013): I have made modifications to these slides, in particular, the concentrationtime graphs on Slides 29, 32 and 36, so that these are consistent with those used in my worked example on the Effect of Changing Conditions on An Equilibrium System.

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