OBJECTIVE:
APPARATUS:
PRECAUTIONS:
You might expect to find , of the
nitrogen by setting
We can avoid this difficulty by noting that
Q is also the heat needed
to warm the same aluminum cylinder
to from T
to T
. You can measure this heat by placing
the cold aluminum cylinder (at temperature
) in a
``calorimeter'' that contains water and
observing the change in temperature of the water,
,
-provided that the
final temperature of the water,
, is room temperature,
. It is hard to arrange for
to end up exactly at room temperature, but if
is close to
, one can accurately correct the calorimeter data for the small
additional heat term, namely
),
since over the small
interval,
is constant.
SUGGESTIONS ON PROCEDURE:
How much of the N
mass change
was caused by the heat from the cylinder? If a-b and c-d were parallel, it
would be the vertical distance between these lines. But
c-d ordinarily has a smaller slope than a-b, possibly because
the evaporation of liquid nitrogen between b and c has cooled the
upper part of the flask.
Hence we use the average of the two rates of fall by drawing
a vertical line through e, (the midpoint of line b-c). Then f-g
estimates the mass, m, evaporated by the heat from the cylinder.
Hence will be the heat to warm the Al cylinder
in the calorimeter to
plus the mass of the
cylinder
(specific heat of aluminum)
.
Specifically if:
= latent heat of vaporization of nitrogen
= mass of nitrogen evaporated by heat from the cylinder
, c
= mass and specific heat of Al cylinder
= initial temperature of water and calorimeter
, c
= mass and specific heat of water
, c
= mass and specific heat of calorimeter and stirrer
h= heat capacity of immersed part of thermometer,
then, if we neglect :
OPTIONAL: