Physical
Science

Heat
of fusion and evaporation

This page ** and
the top half of the second page **are to be completed before you report
for lab.

__Define__:

1) heat of fusion -

2) heat of evaporation -

3) specific heat -

4) calorimeter -

5) Explain, using complete sentences, what the
equation below says. The symbols used
are those from the lab sheet (so you must read the entire lab before
answering).

The heat necessary to
change the temperature of a certain quantity of water from T_{i}_{
} to T_{f}
is given by the expression:

Mw (Tf - Ti) Sw

Read all of this experiment, then tell what each
of the following symbols represents.

6) Mc =

7) Ti =

8) Tf =

9) Sc =

10) he =

11) hf =

12) Mw =

13) Sw = Tell what
this is and give the value in cal/gr Sw =

14) When
the lab asks for the value of the mass of the can, what other item is always to
be included when the can is weighed?
__________________________

(Be sure the thermometer is never in the can
when it is being weighed!)

16) **Before coming to the lab, do the questions
on the last page of your lab that are numbered 14, 15, 16, 17, 18, and 19. **

TO BE DONE
IN LAB (Read before coming to class)

__Object__: To study how energy
causes temperature changes and changes of phase (solid to liquid and liquid to
gas).

__Specific Heat__: To do this
experiment, you will need to understand the concept of specific heat. __(The
amount of energy necessary to change the temperature of 1 gram of substance,
one degree Celsius).__

__General Procedure:__
The energy from melting ice and condensing steam will be used to change the
temperature of a known amount of water, and the energies of fusion and
evaporation of water will be calculated from this data.

A calorimeter is container that is designed to
lose as small an amount of heat to its surroundings as possible. The calorimeter you will use uses an air
layer as an insulator (it is essentially a can within a can). You will need to
include the inside can in your calculations as it will absorb some heat energy
as its temperature changes.** The metal stirrer will always be included as
part of the can when weighing the can, both when empty and when it contains
water.** The specific heat of this can
is usually stamped in it. You will need to weigh it to determine its mass.

**Caution: Do not put the ice in your mouth as it
is not clean!**

__Procedure:__ Each person will work by themselves on this
experiment.

1) Weigh the inner calorimeter cup with the
stirrer.

(Be sure it is dry before weighing) Mass = mc = ____________
grams

2) Record its specific heat Sc =
_____________ cal/g Co.

(Number stamped on can
or ask instructor)

3) Fill the inner cup about half full of warm
tap water (about 45 degrees Celsius), and weigh on the balance to determine the
exact amount of water added.

a)
Can + Water = _____________________ g

b) Empty can (see 1) = ________________ g

3) (a - b) mass
of water = ____________________ g (Subtract)

4) Put the inter cup back into the ring in the
calorimeter. Put the lid on the calorimeter and place a thermometer in the
large hole, and the stirring rod in the small hole. Stir it well.

5) Record the temperature of water just before
adding ice

6) Take your calorimeter to the front of the
room. Your instructor will add some ice
when you request him to do so. Do not
add the ice yourself.

7) Stir, constantly observing the temperature,
record the lowest temperature reached after all the ice has been melted Tf =______

8) Weigh the can with the water and melted ice,
subtract its previous weight to determine the mass of the ice.

M (can+water+ice) =
_____________

Write this same number in the blanks in question
10a and in 12b, place a check in the following blanks when you have
finished. 10a __ 12b__

8b)
M(can+water+ice)_________ - M (can+water)__________ = MI (ice)
_____________.

(8) (3a)

When you are in the lab, you may skip down to
(Eq. 1) on the next page. Write your
values on top of the symbols in that equation.
The purpose of the explanation below is to show you how the equations
for determining the heats of fusion and vaporization are obtained.

9) The heat absorbed by the melting ice cools
the water and the can. The equation is
:

heat gained by ice =
heat lost by water + heat lost by can

where:

a) heat lost by water = (temperature change of
water) x (mass of the water) x (specific
heat of water)

= (Tf - Ti) x Mw x Sw

b) heat lost by can = (temperature change of can)
x (mass of the can) x (specific heat of
can)

= (Tf - Ti) x Mc x Sc

c) heat gained by ice water = (heat of fusion) x
(Mass of ice) + (temperature change of the water after melting) x (mass of
water)

= (hf) x MI + MI x (Tf - O oC) x Sw

The full equation then
becomes

hf x MI + MI (Tf - O oC) x Sw = (Tf - Ti) x Mc x Sc + (Tf - Ti) x Mw x Sw

And the heat of Fusion
is given by: (Write your numbers on top of the symbols in the equation below.)

(Ti - Tf) (Mc x Sc ^{+ M}^{w}^{
x S}^{w}^{)}
- MI Tf

(Eq. 1) hf =__________________________________________

MI

use this equation to
calculate hf

(show your work) Write
your answer below

hf = heat of
fusion of water = _________________________

10) If you have not changed the contents of you
cup since the last weighing, record the values below. If something has changed, re-weigh and record
the values.

a) weight
of can + water = ____________ (from item 8, the melted ice is now water also!)

b) Mc = weight of
empty can = ___________ (from item 3)

(a - b) Mw = weight of
water = _____________

(Subtract these two to
obtain the weight of the water.)

11) Record the temperature of the water, just
before adding the steam

Ti =
____________C.

__When using the steam generator the utmost
caution must be used to ensure no one is burned!!!__
Do not attempt to use this unless instructed to do so be the instructor!

Run steam from the
generator through your solution until the temperature reaches about 40 ^{o}C.
Stir well for a few seconds and read the final temperature Tf = __________.

12) Again weigh the inner can, stirrer and
water. ______________

(12 a)

M (can+water+steam) - M (can+water) = Ms (steam)

Ms (steam) = ____________________ -_____________ =
________________

(12
a) (12 b)

When in lab, you may now skip to (Eq. 2) on the
next page.

13) The heat lost by the steam is gained by the
water and the can. The equation for this is (heat lost by steam) + heat lost by
water (formed when the stem condenses) and as it changes from 100 ^{o}C
to Tf = heat gained
by water.

heat
lost by steam = (mass of steam) x (heat of evaporation of water) = Ms x he

heat
gained by water = mass of water x temperature change x specific heat

= Mw (Tf - Ti) x Sw

heat
gained by can = mass of can x temperature change x specific heat

= Mc x (Tf - Ti) x Sc

heat lost by the water
after condensing from steam

=
Ms x (100 - Tf) x Sw

The full equation is
then:

Ms x he + Ms (100 - Tf) x Sw = Mc (Tf - Ti) Sc + Mw x (Tf - Ti) x Sw

And solving for he, we have:
[Write your numbers on top of the symbols below.

Note that the values
of Tf, Ti and Mw are all
different than in the previous problem. Mc and Sc are unchanged.
(Write your numbers on top of the symbols in the equation below.

(Tf - Ti) (Mc Sc + Mw Sw) - Ms (100 - Tf)

(Eq. 2) he =
________________________________________________

Ms

(show your work) use
this equation to calculate he =
____________________

14) Look up the following information in your
text or use your lecture notes. Do the
calculations indicated. (include units in all your
answers)

15) Heat of fusion of water (in Joules/gram)
__________________

16) Number of Joules/calorie ___________________

17) Use the number in 16) to convert the heat of
fusion (item 15) to calories/gram._____________________________

18) The heat of evaporation of water in
Joules/gr. from your text (including units) is
___________________________________________

19) Change this to calories/gram.
________________________

20) Calculate the % error of hf (clearly show
your work)

% error = __Correct answer(from question 17) -
Answer from Eq. 1__

Correct
answer (from question 17)

In the first blank substitute the numbers from
your experiment.

% error in hf =
_____________________________________ = ____________

(Show work)

Substitute in your
values then show the final result.

19) Repeat the calculation to find the % error
of he.

(Compare your answer from Eq. 2 to that from
question 19)

Show your work as in 20.

% error in he =
_____________________________________ = _________

(Show work)

Tell some things that can cause errors in this
experiment and what can be done to improve them.