In this experiment, the heat of ionization of a weak acid was investigated.
According to the first law of thermodynamics, the total internal energy is equal to q, the
heat energy gained by the system and w, the work done on the systemL: ∆E = q + w
At constant pressure the equation becomes ∆E = q
- P∆V where q
is the change in heat
content of the system at constant pressure. This is the change in enthalpy.
∆H = H
= ∆E + P∆V
In this experiment, a Styrofoam cup calorimeter was used to measure heats of
reaction since it is a reasonably good insulator. The temperature change from a reaction
inside the calorimeter can be measured, since the total heat capacity of the system (the
calorimeter and its contents) are known, the change in heat content can be calculated with
the formula: q
is the total heat capacity of the system at constant
pressure and ∆T =
The heat capacity of the calorimeter is determined experimentally to measure the
temperature change resulting from mixing inside the calorimeter two known quantities of
water initially at different temperatures.
If there is no energy loss then,
| heat lost by hot water | = | heat absorbed by cold water | + | heat absorbed by the calorimeter|
However, since the calorimeter is not perfect insulator there will be some sources of error.
To correct for these errors, changes in temperature are determined graphically. In studying
chemical reactions it is important for the mixing of two reacting solutions to be performed
very quickly so that the temperature can be measured right away and prevent any further
heat leakage. This allows for the most accurate possible results when plotting temperature
versus time. In the graph, the portion of the initial period required for the system to mix