Procedure – PASCO ET-8499 Energy Transfer Calorimeter User Manual

Page 14

Energy Transfer Calorimeter

Experiment 2: Entropy

Completing the integral yields the final relationship

Note that entropy is a state function. The change in entropy depends only on the initial and final
conditions, not on the process involved.

In this experiment, hot water is mixed with cold water in an aluminum calorimeter cup. The cold
water and aluminum cup have the same increase in temperature and can be considered as one part
of the system. The hot water which is added to the cup is the other part of the system. The change
in entropy of each part of the system is calculated using equation (3).

The sign of

∆

S will not be positive for both parts of the system. In general, a positive change in

entropy indicates a process which tends towards a higher state of disorder. As you can see from
equation (1), if dQ is positive, the change in entropy is positive, and that means (for this
experiment) that the temperature is increasing. An object at a higher temperature has faster-
moving molecules, and in general is in a more "disordered" state.

Procedure

Measure the mass of the inner aluminum cup from the Calorimeter. Only the inner cup
changes temperature and is part of the experiment. The outer (bigger) cup acts only as a
holder, and due to the air gap in between, helps to insulate the inner cup.

Add about 30 g of "ice" water to the inner cup. You want very cold water, but make sure there
is no ice in the cup.

Measure the mass of the cup plus water and calculate the mass of the cold water.

Assemble the cup, using the spacer to suspend the inner cup inside the bigger cup. Put on the
lid, and use the one hole stopper in the hole to hold the thermometer.

Pour about 100 g of hot water into an insulated cup. Place a second thermometer in the hot
water.

Gently stir the water, and record the initial temperatures of the hot and cold water to a
resolution of at least 0.1°C. Pour about 30 g of hot water into the calorimeter cup. You want at
least 1 cm above the water line to the top of the cup. Replace the lid and watch the
temperature of the water. Gently swirl the water and record the final equilibrium temperature.

Place the other thermometer (from the hot water) in the same water (in the Calorimeter cup),
and check to see if it reads the same value. If not, measure the offset and adjust your values
accordingly.

Remove the inner cup and determine the mass of cup and water. Use this to calculate the mass
of hot water you added

∆

mcln

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 

 

(3)