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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: iaoveladamaa on November 14, 2007, 05:52:34 PM

Title: Styrofoam Vs. Glass
Post by: iaoveladamaa on November 14, 2007, 05:52:34 PM

I apologize. I am new to the website and have asked the question as a poll. =\

My question is:

How does using a glass calorimeter affect ∆H instead of styrofoam? Are values higher or lower? Explain.

Thanks a lot in advance.

Title: Re: Styrofoam Vs. Glass
Post by: agrobert on November 14, 2007, 07:29:36 PM

  
     When you use glass you have more heat transfer (hot to cold) from the internal environment to the surroundings.  Theoretically delta H will be the same whether you do your reaction or experiment in glass or Styrofoam but experimentally you will inevitably record lower temperatures in your glass calorimeter making the calculated value delta H smaller. 
     
     This experiment is best done with two Styrofoam cups, one inside the other.  I assume you record T_i and T_f.  If you allow the glass or cup to equilibrate (10 minutes-room temperature) with your water (example) and then record T_i it should be the same for either instance.  When you add your hot metal (example) and record T_f you will transfer (lose) more heat to the surroundings in the glass, therefore you record a lower (incorrect) T_f, which results in a smaller delta T and smaller delta H.  The insulation of the Styrofoam reduces this error.