Temperature Lab Thoughts

So, you did the lab, and I graded it, but here are some things that you all should be thinking about.

  1.  All percent error calculations must have a sign.  A positive sign means your measure is greater than the actual.
  2. A negative sign means your measure is less than the actual.
  3. No sign means that you are not thinking, or don’t care.  Not okay.
  4. The freezing point represents the phase change temperature between liquid and solid.  For water it’s 273 Kelvin or zero centigrade.
  5. The melting point represents the phase change temperature between liquid and solid.  For water it’s 273 Kelvin or zero centigrade.
  6. For ALL SUBSTANCES, the freezing point temperature = the melting point temperature.
  7. As it turns out, the HOT phase change (boiling and condensation) also have one temperature.
  8. If you could hold the temperature steady at say 273 Kelvin, water would be in the liquid phase, and the solid phase at the same time, both would coexist.
  9. If you could hold the temperature to 100 centigrade (373 Kelvin) you could have both boiling water and condensing steam, at the same time,
  10. The hottest part of a Bunsen burner flame is the INNER CORE, not the bottom or top of the fire.  The inner core, AKA the “cone of pain”.
  11. Absolute Zero is a “theoretical temperature”, it does not exist anywhere.  If there were a spot in our Universe, so far from any star light that it has NO ENERGY at all, you could say it has a temperature of 0 Kelvin.  But, just the observation of such a place, from ANY distance, would impart some energy to that spot, which bumps it up to slightly more than zero Kelvin.  OK is fun to think about, but not real.  If a place had that temperature, even the movement of the electrons would cease.  Literally nothing would or could happen. In a real way (hard to understand though) where there is zero Kelvin, there is also NO TIME.  That’s a bit of a paradox.  Zero Kelvin is not possible, but it WOULD BE the lowest possible temperature, a zone of literally NO ENERGY.
    Also, Kelvin doesn’t use “degrees”, just Kelvins.  This is a non-science major cartoon, funny on many levels!

  12. The change in temperature question is not graded, it’s hard, and I need to warm you up to this many times before you will finally let it in.  Here goes…Question 17 says: “the temperature of a solution changes from 12.0ºC to 29.0° C.  That means that the temperature increases by 17.0 C.  We could use the “delta” symbol, which means change in, so the ΔT = 17.0°C.

    The question was what is this change in Kelvin?

    This is a tricky question.  Most of you thought it said, what does17.0°C equal in Kelvin?  It does not.

    It says instead, if the temperature of this solution changes by 17.0°C, what would be the change in temperature in Kelvin?

    Let’s first change the original temps into Kelvin, then get their difference.  Using our formula of K = C + 273, our original temps are 285 K and it warms to 302 K.

    The difference in Kelvin would be 302 K – 285 K = 17.0 Kelvin.  We say the ΔT = 17.0 K.

    The temperatures are not the same, but the difference is the same. 

Think about this, how old are you?  Write that number on a piece of paper.  I am 61.  We are NOT the same age.  Now, in FIVE YEARS, how old will you be – do the math.  I will be 66 (wow).  Will we be the same age in five years (no).  Did we “change” the same number of years (yes) . Our ΔT is the same, but our ages is not.

The reason is that my “starting point” is 1960.  You were born in a different year.  I started way earlier than you.  Kelvin “starts” at absolute zero, but centigrade “starts” at a different place, 273 Kelvin = 0°C.  The temperatures never equal each other, like our ages never equal each other’s, but we change in the same amount.

This solution has a ΔT of 17.0 K.  It also happens to have a ΔT of 0°C

The start temps were different from each other, and the end temps are not the same either, but the change is the same.

The ΔT Kelvin = the ΔT Centigrade, but the actual numbers used to determine that change are not the same.