Pasco TD-8557 Basic Calorimetry Set Manuel d'utilisateur télécharger pdf (Page 4)

Basic Calorimetry Set

Notes on Calorimetry

A calorimeter is a vessel or device that thermally isolates an experiment from its surround-

ings. Ideally, this means that the results of an experiment performed in a calorimeter are

independent of the temperature of the surroundings, because no heat flows into or out of

the calorimeter.

However, no calorimeter is perfect, and there is always some unwanted and unaccountable

heat flow affecting the results of any calorimetric experiment. To minimize unwanted heat

flow, always plan the experiment to follow these rules:

1. The time between the taking of initial and final temperatures is minimal.

In other words, do the critical portion of the experiment quickly, so there is minimal time

for unwanted heat flow between measurements. (Don’t rush; just plan carefully.)

2. Whenever possible, room temperature is approximately midway between

the beginning and ending temperatures of the experiment. When the experi-

mental temperature is colder than room temperature, heat flows from the surroundings

into the calorimeter. When the experimental temperature is hotter than room temperature,

heat flows from the calorimeter into the surroundings. If the experimental temperature

varies above and below room temperature by equal amounts, the heat gained and lost to

the environment will be approximately equal, minimizing the net affect on the experiment.

3. Mass measurements of liquids are made as near the critical temperature

measurements as possible. This reduces the effects of mass loss by evaporation.

Measuring liquid masses by taking appropriate differences is a useful technique (see the

instructions in the individual experiments).

NOTE: In applying the above rules, it is often helpful to perform a quick preliminary experiment to

determine the best choice for initial masses and temperatures.

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Pasco TD-8557 Basic Calorimetry Set Manuel d'utilisateur Page 4