PhysicsLAB: Specific Heat

The purpose of this lab is to determine the specific heat of a small metal cylinder. This will be done using calorimetry along with a LabPro temperature probe and the law of heat exchange.

Under the Start Menu go to Programs, Math, Logger Pro 3.1 to launch the program.

Logger Pro should automatically set up the graphs according to the connected sensor. With a temperature probe properly connected, the program should display a graph of temperature vs time. When you are ready to start collecting data, press Collect to start timing; then begin the experiment.

Equipment

Each group will need the following

LabPro with temperature probe
triple beam balance
1 dry styrofoam cup
hooked metal specimen
50 ml of cold water (just enough to submerge your specimen when it is placed in the cup)
one beaker for boiling water
one hot plate
string to suspend specimen in hot water

Data

type of metal specimen

Data Table I

	mass
description	(kg)

empty strofoam cup

cup with cold water

cold water only

metal specimen

Once the water in the beaker is boiling, suspend the metal specimen in the hot water. Use your probe to verify that the water is boiling at 100ºC. It will take very little time for the metal to reach thermal equilibrium. Next dry off the probe and set it in the cup of cold water and record its initial temerature. You can start and stop collecting temperature data arbitarily during this portion of the experiment. It is only critical that your record stable temperatures for both the cold and hot water.

Prepare to collect data for the final temperature by setting the duration to collect data for 2 minutes. When you are ready to transfer the hot metal specimen into the cold water, quickly, but carefully, move it into the COLD water cup. Try not to allow any hot water to be transfered with the specimen by letting the steam assist in "drying" off the specimen. Also note that no water should splash from the COLD water. Use the temperature probe to gently stir the mixture - record the final equilibrium temperature. Do NOT rest the probe against the metal specimen. ALERT: The change occurs quickly - watch your screens for the PEAK temperature after the specimen is transferred!

Data Table II

	temperature
description	(ºC)

initial temperature of cold water

initial temperature of specimen

final temperature water/specimen

Calculations and Conclusions

When there is no phase change, the heat lost or gained by an object can be calculated with the formula: Q = mcΔT.

m is the mass of the object in kg
c is the specific heat of the material in J/kgCº
ΔT is the change in temperature in Cº and is always expressed as T_f - T_o

The Law of Heat Exchange states that in a confined system, when thermal equilibrium has been reached, the heat lost by one object will equal the heat gained by the other.

ΣQ_lost + ΣQ_gained = 0.

Note that Q_lost will be negative (since T_f < T_o) and Q_gained will be positive (since T_f > T_o). In our experiment, the cold water sample gained heat and the metal specimen lost heat. The accepted value for the specific heat of water is 4186 J/kgCº. We are assuming that the styrofoam acts like a thermal insulator and does not gain or lose any heat.

Based on your mass and temperature data, calculate the experimental specific heat of your specimen in J/kgCº.

According to your textbook, what is the accepted specific heat for the metal composing your specimen in J/kgCº?

Calculate a percent error for your experiment.

Discuss what your group feels is this lab's greatest source of error.

State a valid procedure that could minimize your error's negative consequences when the lab is completed next year.

When you are finished with the experiment, close LoggerPro, dry off the probe, empty your water samples into the front sink and turn your empty cups upside down on a paper towel to dry out for next period.