PC1221 Lab Report: Ideal Gas Laws
Wang Zhikai
A0080959N
Group A1
PC1221 Lab Report: Ideal Gas Laws
Wang Zhikai
A0080959N
Group A1
1
Objectives
To demonstrate that the pressure
P
of a gas at a fixed temperature is proportional to the quantity
(1/
V
) where
V
is the gas volume.
To demonstrate that the volume
V
of a gas at a fixed pressure is proportional to the temperature
T
of
the gas.
To determine an experimental value for the constant that relates Celsius temperature
T
C
to the
absolute temperature
T
.
To determine an experimental value for the atmospheric pressure Pa.
2
Introduction
All gases can be described by the three variables of volume
V
, pressure
P
and temperature
T
. If we
assume that the density of the gases is low, we call the gas in question an ideal gas. Although there are
no true ideal gases, most gases behave to a good approximation as ideal gases near room temperature
and atmospheric pressure. The ideal gas law is given by
PV
=
nRT
, where
n
is the number of moles for
the gas and
R
is the universal gas constant with a value of 8.31441 JK
1
mol
1
. The SI units of pressure
P
are N/m
2
and the SI units of volume
V
are m
3
. When using this equation, the temperature is always
expressed as the absolute temperature in Kelvins. The relationship between temperature in Celsius
T
C
and the absolute temperature in Kelvins
T
is given by the equation
T
=
T
C
+
T
O
. However, each Kelvin
is similar in magnitude to Celsius; therefore the difference in temperature is the same whether it is in
Kelvins or Celsius.
Using the ideal gas law, we can create several scenarios where we keep one of the three variables
describing air as a constant in order to vary the other two to obtain experimental values for the
constants involved in the law. We can keep the amount of air quantity fixed at a constant temperature.
With the amount of air fixed,
n
is a constant, and with the temperature fixed, so is
T
. Thus, we can
designate
nRT
as a constant
C
1
. We can then rewrite the ideal gas law equation as
P
=
C
1
(1/
V
), also
known as Boyle’s Law.
In order to vary the pressure of the gas, we use a measuring tube with mercury in it and compare the
height difference between the height of the mercury in the measuring tube and the mercury level in the
reservoir. For us to measure the pressure of the gas in a measuring tube, we can divide the pressure
P
in
the measuring tube into two parts, the atmospheric pressure
P
a
and the additional pressure as the gauge
pressure
P
g
.
P
g
is caused by any height difference
h
between the two mercury levels and is calculated
with the equation
P
g
= p
gh
and is given as 0.1333kN/m
2
mm
1
h
. By substituting
P
a
+
P
g
for
P
in Boyle’s
Law, we obtain
P
g
=
C
1
(1/
V
) 
P
a
.
When we consider the situation with a fixed amount of gas and a constant pressure
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 Spring '11
 Tan

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