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Talk Chemistry

There have been all sorts of discussions on Talk Chemistry recently.

Leonard Winning responded to our  Endpoint article on students writing assessments:

I really like the idea of  Peerwise: I've registered and am trying it out with my L6 at the moment - the initial response has been very positive. Has anyone else tried this in a school rather than university environment? 

Mick Mahon posed this question: 

We teach that adding a catalyst to an equilibrium system does not alter the position, just the rate of equilibrium attainment, because it increases the forward and backward rate by the same amount. Why and how can that be? The activation energies will be different for the forward and backward direction. Does a change in forward/backward pre-exponential factors somehow exactly cancel the difference in E_a? Seems hard to believe. Or is it some outcome from the Boltzmann distribution curve? Or some other reason?! 

Nessa Carson proposed an answer: 

The forward and back activation energies are the same - it goes forward, and back, along the same graph. The line represents moving along the reaction coordinate, which is basically 'how much' the reaction is done. You can think of the reaction as 'moving' along the graph. 

This is the principle of microscopic reversibility! There's a Wikipedia page if you're interested in more, including a small amount of physics unlikely to come up in your chemical studies. 

Alan Goodwin was another who responded: 

I believe the position of the equilibrium is dependent on the (free) energy difference between the reactants and the products. This is independent of the pathway between them used by the reaction and thus changing the pathway cannot change the position of the equilibrium.

Andres Tretiakov posted a video of an activity he assisted with that demonstated the properties of liquid nitrogen. This provoked a conversation regarding the Leidenfrost effect and to the extent it prevents human skin from being damaged by contact with liquid nitrogen: 

I have done this demonstration dozens of times and I warn the audience and everyone else beforehand that this should not be emulated. Once they realise that our bodies are mainly water and that water freezes at 0^oC, then they get the picture of the consequences of handling liquid nitrogen irresponsibly. 

Dave Warren suggested a way to demonstrate this: 

We are always being asked 'what happens if you put your hand into it?' So we've started using mandarin segments to illustrate the danger of liquid nitrogen, they freeze beautifully, crack open and then if you squeeze them gently they shatter into tiny segments. When they thaw (individual segments can be held in the hand within 30 seconds of coming out of the nitrogen) the audience can see that the segments are like burst balloons with all the juice outside so the discussion can lead into the expansion of water. 

Join in the discussions and carry on the debate on the Talk Chemistry website

Top tweets

Here are some of our favourite tweets this issue:

• The story that provoked the most response last issue was 'Ofqual ponders if A-level chemistry contains too much maths'  
  John Dexter (@DexNott) said:
  Ofqual need to look carefully at content of specs vs assessment model. May look like too much of anything BUT depends if in exam
  
  David Read (@lowlevelpanic) was brief in his response:
  Ofqual is off its rocker!
  
  Simon (@doc_gnome) pointed out:
  Didn't SCORE say not enough?

• Simon also had a comment on the article 'Criticism of maths in chemistry grows. 
  Interesting article from @RSC_EiC. Does A-level chemistry prepare pupils for uni?

• On a different topic, Anthony Brown (@BrownieAJ) discovered something that we're sure many chemistry teachers will find useful:
  Alt+8652 just made my K_c lesson planning a lot easier. How did I not know this ???? Fool.
  If this is news to you, try it yourself in Word as an easy way of producing the  character.

• Last issue we announced the winners of the 2012 RSC education awards.
  The chemistry department at the University of Reading (@UniRdg_Chem) pointed out:
  Including our David Wright!
  
  There was praise for Michael Seery from @Ordinary_Times: 
  Congrats on the award Michael.
  A man of many talents!

• Layl M de De Sedas (@LaylMarie) was brief and to the point in her reaction to our Endpoint article on students writing assessments
  Intriguing

• Finally, David Smith (@professor_dave) had this to say to about some recent UK success:
  Chemistry has its own Olympics. And the UK medalled!!