Revised 10/03,2/06
Experiment 10: Calorimetry
Purpose
(1) To study heat transfer processes, including those involving phase changes.
(2) To measure the heat of fusion of water (latent heat).
Apparatus
calorimeter; dial balance; a beaker with some water at room temperature; a spare beaker;
supply of ice; paper towels; and more water at room temperature on the side.
Theoretical Summary
(A) When heat is absorbed or emitted by a certain mass of a substance, without a
change in phase (solid, liquid, or gas), the amount of heat Q is given by formula (1),
where:
M = mass
Tf = final temperature
Ti = initial temperature
C = specific heat for the particular substance
BASIC FORMULA
(1)
Q = M · C (Tf – Ti)
Note: If Tf > Ti the heat is absorbed; if Tf < Ti the heat is emitted.
Remark: the specific heat C is, in general, different for different phases of a substance,
in particular, it is different for ice and water.
(B) When the phase of a substance changes,
BASIC FORMULA
this process takes place at a constant
temperature. The amount of heat Q
absorbed or emitted in this process is
(2)
Q=M·L
given by formula (2) where:
M = mass
L = latent heat
Note: If the change of phase is between the solid and a liquid (as in ice/water) L is
known as the latent heat of fusion.
The Calorimeter: This is an apparatus designed to provide thermal insulation (ie no
exchange of heat) between its CORE (the interior cup with its contents plus the stirrer)
and the SURROUNDINGS (mostly the air in the room). The insulation consists of the
jacket, the lid, the thermometer, and the rubber ring.
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Experiment 10
Procedure Part I.
(a) Set up the Table I on your data sheet. Measure all temperatures to 0.1º C.
TABLE I
Mcs
Mcsw
Mip
Mpap
------- All in Grams ------
Mf
T0
Tice
Tf
------ All in ºC ---
(b) Remove the interior cup of the calorimeter, together with the stirrer, (but without the
rubber ring) and record its mass (cup + stirrer) as Mcs.
Put approximately 200 gm of water (should be available in a beaker) into the cup and
record the total mass (cup, stirrer and water) as Mcsw.
Close the calorimeter and record the initial temperature of the water as T0. (This
should be the room temperature - if in doubt, check with your instructor).
(d) Take about 50 grams of ice, put it on a piece of paper towel and record the total mass
as Mip. Immediately after this, put the ice into the calorimeter along with the water
and close it.
Measure the mass of the paper and record it as Mpap. Also, record the initial
temperature of the ice as Tice.
(e) Keep watching the thermometer for several minutes, and move the stirrer once in a
while, until the temperature ceases to fall. This will be the final equilibrium
temperature (which should remain steady for another 5 minutes).
When you believe this temperature is reached, open (and close) the calorimeter
quickly to check if all ice has melted (if it didn’t, you should wait a bit longer).
Record the final equilibrium temperature as Tf.
(f) Remove the cup, with the stirrer and the water contained in it, and record this mass as
Mf. Check whether Mf + Mpap equals Mcsw + Mip accurately to within 0.5 grams,
(If not, check all your measurements before you proceed further.)
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Experiment 10
Procedure Part II.
(g) Wipe all parts of the calorimeter with paper towel and let them dry out completely at
room temperature. In the meantime, set up Table II on your data sheet:
TABLE II
Mcs
Mcsw´
Mip´
Mpap´
------- All in Grams ------
Mf´
T0´
Tice
T´
------ All in ºC ---
(h) After all parts of the calorimeter are completely dry, put approximately 100 grams of
water at room temperature into the cup and record the total mass as Mcsw´. Close
the calorimeter and record its initial temperature as T0´ (this should be the same as
T0 in Part I).
(i) Take about 80-100 gm of ice, put it on a piece of paper towel and record the total
mass as Mip´. Immediately after this, put the ice into the calorimeter and close it.
Measure the mass of the paper and record it as Mpap´.
(j) Keep watching the thermometer, and move the stirrer once in a while, until the
temperature reaches its lowest point. (This may take up to half an hour.) Record
this temperature as T´ (it should be definitely less than 2ºC).
Open the calorimeter and quickly pour out all water, leaving only the unmelted ice.
Quickly weigh the cup with the stirrer and unmelted ice in it and record as Mf’.
BEFORE YOU LEAVE THE LAB: WIPE OUT YOUR CALORIMETER WITH
PAPER TOWELS AND LEAVE IT OPEN TO DRY OUT.
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Experiment 10
Lab Report
Part I.
(1) On the basis of formulae (1) and (2), the following equation represents the heat
exchanges involved in Part I:
Mcs · C0 · (T0 – Tf) + Mw · Cw · (T0 – Tf) =
Heat emitted by the
Cal. Cup & Stirrer
Heat emitted by the
original water
= Mice · Cice · (0 – Tice) + Mice · L + Mice · Cw · (Tf – 0)
Heat Absorbed by Ice
Until it is Heated to 0ºC
Heat needed
for Melting
Heat Absorbed by
Molten Ice
(2) Solve this equation for L (heat of fusion of water) using the specific heats
C0 = 0.22 cal/gm. ºC (calorimeter); Cice = 0.50cal/gm. ºC (ice);
Cw = 1.00 cal/gm. ºC(water).
(3) Display your % error by comparing to the correct value of 80 cal/gm.
Part II.
(4) On the basis of formulae (1) and (2), display the equation representing the heat
exchanges involved in Part II (similar to equation (3), explaining each term, as has
been done there).
Denote this equation as (4).
(5) Using L = 80 cal/gm, calculate from your equation (4) the amount Mmelted-calc of
the melted ice, and compare it with the measured value (given by
Mmelted-meas = Mcs + Mip΄ - Mpap΄ - Mf΄). Display the % discrepancy as
follows:
% DISCREPANCY = Mcalc- Mmeas
Mmeas
50
x 100%