Lecture 20 – Temperature Conversions

The measure of intensity of heat of a substance is called temperature.  A thermometer measures temperature.  Temperature is measured in three different units: Fahrenheit (degrees F) in the United States, Celsius (degrees C in science and everywhere else on the planet), and Kelvin to measure absolute temperature.  Below you can see how the temperature systems compare.

Fahrenheit                                Celsius                                     Kelvin

212                                          100                                          373

176                                          80                                            353

140                                          60                                            333

104                                          40                                            313

68                                            20                                            293

32                                            0                                              273

-4                                             -20                                           253

-40                                           -40                                           233

A comparison of the three temperature scales shows their differences clearly.

 

The conversion factor for Celsius to Fahrenheit is:

t(F) = [t(C)  x 1.8 F/1 degree C] + 32 = [t(C) x 1.8] + 32

The conversion factor for Fahrenheit to Celsius is (hint: subtract 32 so that both numbers start at the same temperature!  This is so easy!

t(C) = [t(F) – 32 degrees F] x 1 degree C/1.8 degrees F = [t(F) – 32]/1.8

or a simpler way to say it is:

degrees C = 5/9 (degrees F – 32)

Tip:  If you believe in buying stock, buy stock in 3×5 cards.  I have very nice files for my 3 x 5 cards.  The cards are neatly indexed by subject matter and banded together.  I am quite patient when need to wait in a line because I always have subject matter in my handbag to review.  If you are the ‘brightest bulb on the Christmas tree’, that is great.  If not, just be the most disciplined and hardest working.

Let’s work a few examples before we part company.

Example 1:

A summer day in Hawaii might be 21 degrees Celsius.  What is that in Fahrenheit?

21 degrees C = 5/9 (degrees F -32)

21+ 32 = 5/9 degrees F

53 x 9 = 5 degrees F

477/5 = 70 degrees F

To obtain absolute zero (the lowest temperature possible), the Kelvin scale is used, where the lowest temperature is zero.  A Kelvin is an SI temperature unit.    The heat energy is zero.

Example 2:

To see how temperature conversion works, let’s convert normal body temperature, 98/6 degrees F, to Celsius.

Degrees C = 5/9 (degrees F – 32)

Degrees C = 5/9 (98.6 degrees F – 32)

=5/9 (66.6) = 37.0 degrees C

Degrees C can be converted to K by adding 273 to the Celsius temperature.

Example 3:

K = degrees C + 273

K = 37 degrees C + 273 = 310 K

There are reactions where heat can play an important role in determining the character of the final compound.  Do well with this information.  Next lecture we get back to bone density and bone structure.

 

 

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