Activity No. 2
CALORIMETRY AND SPECIFIC HEAT
INTRODUCTION
Chemical and physical processes can absorb (endothermic) or release (exothermic) heat.
Chemists and physicists used a technique known as calorimetry, referred to as the science of
measuring the changes in energy of a system by measuring the heat exchange with the
surroundings. It measures the amount of energy given off or absorbed during chemical reactions.
The quantity of heat absorbed or released by a substance depends directly on the type of substance,
its mass, and the temperature changes it undergoes. The calorimeter generally consists of a
container filled with liquid, usually water, a thermometer for monitoring temperature, and a device
for stirring the water. Calculations from calorimetry center on the Law of Thermodynamics that
states “energy cannot be created or destroyed.” When applied to calorimetry, this means that any
heat produced during a chemical reaction must be transferred to the calorimeter, or more
specifically, to the water inside the calorimeter. Therefore, if chemists or physicists can measure
the heat absorbed by the water, then they know the amount of heat given off.
One physical property of a substance that can be determined using the calorimetric method
is its specific heat, defined as the amount of heat required to raise the temperature of 1 gram of
the substance by 1 degree Celsius.
In this activity, a hot metal is placed inside the calorimeter containing water. Inside the
calorimeter, the hot metal releases heat, which in turn is absorbed by the water and the calorimeter.
The heat released by the metal is equal to the heat absorbed by the calorimeter and the water based
on the equation shown:
Heat released (Q) = Heat absorbed (Q)
Heat released by metal = Heat absorbed by the calorimeter + Heat absorbed by water
Qmetal = Qcal + Qqwater
(mmetal Cmetal ∆Tmetal) = (mcal Ccal ∆Tcal) + (mwater Cwater ∆Twater)
Where:
m = mass in grams
C = specific heat of a substance
∆T = change in temperature
The specific heat of common metals is found in the table below:
Table 4.1.Specific Heat of Common Metals.
Metal
Aluminum
Brass
Copper
Iron
Lead
Magnesium
Tin
Water
Specific Heat – C
(J/g°C)
(Cal/g°C)
0.910
0.220
0.380
0.090
0.390
0.092
0.460
0.108
0.130
0.031
1.050
0.243
0.382
0.054
4.184
1.000
OBJECTIVES
At the end of the activity, you can:
1. calculate the amount of heat absorbed/released by a metal;
2. calculate the specific heat of a given substance (metal);
3. compare experimental data with the established or theoretical value on specific heat of the
metal used;
4. calculate percent error; and
5. explain the result on the obtained percent error.
APPARATUS/MATERIALS
1-Aluminum calorimeter
1-Wire gauze
1-Beaker (250 mL)
1-Thermometer
1-Alcohol lamp
1-Platform balance
1-Metal sample (150-200 grams)
1-Iron stand with ring / tripod
1-Iron clamp
1-Rubber stopper (one-hole)
1-String (1/2 meter long)
Tissue paper
Styrofoam crap / saw dust
PROCEDURE
1.
2.
3.
4.
Insulate the calorimeter with scrap Styrofoam or saw dust.
Weigh the inner vessel of the calorimeter.
Weigh 150 mL of water in the pre-weighed inner vessel of the calorimeter.
Set the thermometer using one-holed rubber stopper. Adjust the thermometer so that the bulb
will be immersed in the water after the metal is placed and that it does not touch the inner wall
of the calorimeter (Figure 4.1).
Thermometer
Stirrer
Rubber stopper
Metal mass
Insulator
Figure 4.1. Calorimeter Setup.
5. Allow the contents to stand for 10 minutes to equilibrate and take the temperature of the water
inside the calorimeter. Record this as the initial temperature, ti, of the water and the calorimeter.
6. Half-fill the 250 mL beaker with water and positioned it on the ring of the iron stand.
7. Weigh a metal sample.
8. Using a string, tie the weighed metal with a string and hang it above the beaker. Adjust it such
that the metal sample will be totally immersed in the water but not touching the bottom of the
beaker (Figure 4.2).
Iron
clamp
String
Metal Sample
sample
Figure 4.2. Heating of Metal Sample.
9. Heat the water in the beaker to boiling and leave it for 3 minutes.
10. Take the temperature of the boiling water and record it as the initial
temperature, (ti)m, of the metal.
11. Remove the metal from the beaker and immediately tap it with tissue paper
then place it immediately in the calorimeter.
12. Cover the calorimeter quickly and stir the contents with the stirrer. Monitor the
changes in temperature inside the calorimeter.
13. If the temperature do not change anymore or stable for 1 minute, then take
the temperature and record it as the final temperature, (tf)w, of the water,
calorimeter and metal.
14. Calculate the heat gained by the water and the aluminum calorimeter
(q = mC∆t).
15. Using the data gathered, calculate the experimental specific heat of the metal
sample,
C= (qwater + qcal)/(mmetal x ∆tmetal)
16. Calculate the theoretical specific heat of metal sample and compare it to the
experimental specific heat obtained.
1
5. Compute the percent error.
Percent Error =
Theoretical Value – Experimental Value X 100%
Theoretical Value
16. Record all data in the table