NGL VERIFICATION OF GAY-LUSSAC LAWS
The volume of gas changes with the temperature approximately according to the formula:
V = V0 (1 + β t )
(1)
and the pressure of gas according to the formula:
p = p0 (1 + γ t )
For all the gases γ is roughly a constant and has a value γ =
(2)
1
K −1 . However, at a temperature
273,15
t = −273,15 0C is γ t = −1 and thus p = 0 . The pressure of gas would drop to zero, which would mean that at this
temperature the motion of gas particles would stop. It would be natural to assign 0 to the state of the absolute lowest
temperature. The English physicist lord Kelvin realized this and introduced a new temperature scale (with 0 at
t = −273,15 0C ) into physics named after him in which T0 = 273,15 K and β =γ =
1
K −1 ,and then the
273,15
formula (1) can be written in the form:

t 
T
V = V0 1 +  = V0 ,
T0
 T0 
(3)
and the formula (2) in the form:

(T + t ) = p T .
t 
p = p0 1 +  = p0 0
0
T0
T0
 T0 
(4)
Formulas (1) and (2) or (3) and (4) are called Gay-Lussac laws.
For isochoric process, i.e. when the volume of gas is constant, we can write the formula (3) in the following form:
p
= const.
T
(5)
For the gas pressure, then, it follows from this equation that:
p = aT ,
(6)
where a is a constant. The gas pressure is a linear function of temperature with a coefficient of linear regression a .
For isobaric process, i.e. when the pressure is constant, we can write the formula (4) in the following form:
V
= const.
T
(7)
Then the volume of gas obeys the following formula:
V = bT ,
(8)
where b is a constant. The volume of gas is a linear function of temperature with a coefficient of linear regression b .
The goal of this laboratory experiment is to verify the relationship between pressure and temperature of air, which is
enclosed in a glass flask at isochoric process and to verify the relationship between volume and temperature of air,
which is enclosed in a glass flask at isobaric process.
Isochoric process
Laboratory tasks:
1. To measure the dependence p = p (T ) .
2. To draw the graph of the dependence of pressure of air, which is enclosed in a glass flask on the temperature and
to verify that for the constant volume of air the dependence p = p (T ) is linear.
3.
4.
5.
6.
To fit this dependence by an appropriately selected function and to record the values of its parameters.
For all measured values of pressure and temperature to calculate the density of air using the ideal gas law.
To calculate the most probable value of density (mean value) and to calculate its standard uncertainty (of type A).
To use the coefficient a for the calculation of the air density and to compare it with the mean value obtained in
Laboratory Task 5.
Laboratory equipment:
measurement panel CoachLab II+, gas pressure sensor D0341, temperature sensor, glass flask, water bath with heater,
staples, short glass tube, rubber stopper, plastic tubing.
Experimental procedure:
1. In the project Exploring Physics open the file Izochorický dej. Connect the pressure sensor to the channel 1, connect
the temperature sensor to the channel 2 and set the number of measurements in the menu Number of samples for
10. Set the axes of the graph in the p-T diagram.
2. Check the experimental setup according to the scheme (Fig.1). Immerse the whole flask with dry air, which is
connected by means of a thin plastic tube to the pressure sensor, in a cold water bath. Immerse the temperature
sensor into the water in water bath.
3. Turn on the heater and after a slight warming of water start the measurement by clicking on the green button on the
upper panel in the screen. Measure the temperature in the range from 20 °C to 80 °C. Stir water during experiment
in order to have the same temperature in the whole volume of the water bath. The temperature of air in the flask is
assumed to be the same as the temperature of water in the water bath.
4. The experiment can be terminated at any time by clicking on the red button on the upper panel in the screen .
Isobaric process
Laboratory tasks:
1. To measure the dependence V = V ( T ) .
2. To draw the graph of the dependence of air volume in a glass flask on temperature and to verify that for the constant
pressure of air the dependence V = V ( T ) is linear.
3. To fit this dependence by an appropriately selected function and to record the values of its parameters.
4. For all measured values of volume and temperature to calculate the number of moles of air in a glass flask using
ideal gas law.
5. To calculate the most probable value of number of moles of air n (mean value) and its standard uncertainty (of tzpe
A)
6. To use the coefficient a for the calculation of the number of moles of air and compare with the result obtained in 5.
Laboratory equipment:
measurement panel CoachLab II+, gas preassure sensor D0341, temperature sensor, syringe, glass flask, glass tube in
the shape of the letter T, water bath with heater, staples, short glass tube, rubber stopper, plastic tubing.
Experimental procedure:
1. In the project Exploring Physics open the file Izobarický dej. Connect the pressure sensor to channel 1, connect the
temperature sensor to the channel 2. As you will type in the value of volume of air in the Table manually, set the
frequency of scanning for Manual and set the number of measurements in the menu Number of samples for 10. In
order to check the stability of pressure during the experiment in one of the windows you can display the pressure
values in digital form and in the other one you can display the values of temperature. Set the axes of the graph of
dependence of volume and pressure on temperature.
2. Check the experimental setup according to the scheme (Fig.1). Connect the flask with dry air by means of a short
plastic tube to the pressure sensor and syringe and then immerse the whole flask in a cold water bath with heater.
Set the syringe plunger to the position resulting in the minimum volume of air in the syringe. Immerse the
temperature sensor into the water.
3. Press the green button to start the experiment. Heat the water in the heater by a few degrees and then turn off the
heater. Wait until the temperature and pressure stop changing. Set the syringe plunger to the position resulting in
the air pressure value the same as in the beginning of the experiment. Press the green button again and type in the
value of volume of air. The volume of air is the sum of the volume of air in the syringe and the volume of air in the
glass flask. Values of pressure, temperature and volume are gradually entered into the table. Repeat this
measurement 10 times until you achieve the maximum volume of air possible.
4. The measurement can be terminated at any time by pressing the red button on the upper panel in the screen.