Quiz results and more about energy!

For Students:
Hello!  Hopefully everyone's quiz this week went well.  The answers are as follows:
1.  How much energy must be transferred to raise the temperature of a cup of coffee (250 mL) from 20.5 C to 95.6 C.  Assume water and coffee have the same denisty and specific heat capacity (4.184 J/g*K)?
       change in T = 368.8 K - 293.7 K = 74.1 K
       q = C x m x (change in) T
       q = (4.184)(250)(75.1)
       q = 79,000 J or 79kJ

2.  An 88.5 g piece of iron whose temp. is 78.8 C is placed in a beaker containing 244 g of water at 18.8 C.  When thermal equilibrium is reached, what is the final temp.?
       q(metal) = q(water)
       (C (water) x m(water) x (change in temp.)) = (C(Fe) x m(Fe) x (change in temp.))
       (4.184 x 244 x (T(final) - 292K) = (.449 x 88.5 x (T(final) - 352K)
       T (final) = 295K or 22 C

The two above photos show two very important temperatures for water, and for other substances as well.  Everything has a melting and a boiling point.  The energy transferred as heat that is required to convert the substance from a sold at its melting point to a liquid is called the heat of fusion.  On the other hand, the energy transferred as a heat to convert a liquid at its boiling point to a vapor is called the heat of vaporization.  These values are constants for a particular substance and a table with some common values can be found in the back of your book.  It is important to recognize that the temperature remains the same throughout a change of state.  These types of situations will be discussed this week.

For Parents:
Hopefully everyone received their permission slip for our upcoming field trip to the Great Lakes Science Center.  Permission slips must be returned by Friday.  Remember, students will need a bagged lunch on the day of our trip.  Thanks and have a great week.!