PASCO TD-8565 Adiabatic Gas Law Apparatus - Manual (Page 21)

© 2009 Physics Enterprises 21
Experiment 5: Heat Capacity of Gas from
Pressure, Volume, and Temperature Data
Objectives
To illustrate how the abstract mathematics of differential equations can be utilized to obtain
a concrete thermodynamic quantity.
Physical Principles
In physical chemistry the thermodynamic calculations of material properties can be made if
heat capacities of the materials are available. The heat capacity of a gas under constant
pressure, C
p
, defined as (∂V/∂T)
p
, can be derived as C
p
= T(∂V/∂T)
p
(∂P/∂T)
S
. By following the
same principle for the measurement of the heat capacity of a liquid as described in
Reference 1, analogous measurements to determine the heat capacity of a gas can also be
made.
(∂V/∂T)
p
and (∂P/∂T)
S
can be reasonably approximated by finite changes ΔV/ΔT and ΔP/ΔT,
respectively. The change in volume of a gas with temperature can be measured using
standard equipment such as a temperature-controlled water bath and a water manometer.
The change in pressure with temperature requires an apparatus which permits a fast
measurement with negligible heat loss during the change. The Adiabatic Gas Law Apparatus
was chosen because with it a gas could be compressed quickly, and the signals from the
temperature and pressures sensors could be recorded simultaneously.
Procedure
1. Flush the chamber with the sample gas for about 2 minutes. Move the lever up and
down during the flushing to ensure thorough mixing and elimination from the chamber
of air or any previously used gas.
Target Students
Physics for scientists and engineers, physical chemistry, engineering thermodynamics.