Lussac's Law



Lussac's Law was discovered by Joseph Louis Gay-Lussac in the early 1800's. The two different variables that change in this law are pressure and temperature. This gives the relationship between pressure and temperature when volume and amount are constant. The two different variables that stay constant in this law are volume and mass (moles). In 1808, Gay-Lussac came to the announcement that was probably his single-greatest achievement. This came from his own experimentation and others that he has claimed that gases at constant temperature and pressure combine in simple numerical proportions by volume, and the resulting product or products, if they were gases, also are seen as a simple proportion by volume to those volumes of the reactants. This then became known as Gay-Lussac's Law.


First make sure to put on goggles. Then prepare an ice-water bath, and room temp water bath, and a hot water bath. To prepare the Temperature Probe and the Gas Pressure Sensor for data collection, plug the Gas Pressure Sensor into CH1 and the Temperature Probe into CH2 of the computer interface. Next obtain a rubber-stopper assembly with a piece of heavy-wall plastic tubing connected to one of its two valves. Attach the connector at the free end of the plastic tubing to the open stem of the Gas Pressure Sensor with a clockwise turn. Leave its two-way valve on the rubber stopper open until Step 9. Insert the rubber-stopper assembly into a 125 mL Erlenmeyer flask, it is important to twist the stopper into the neck of the flask to ensure a tight fit. Close the 2-way valve above the rubber-stopper---do this by turning the valve handle so it is perpendicular with the valve stem itself. The air sample to be studied is now confined in the flask. Now repeat Step-9 with room-temperature water bath, and the hot-water bath. When you have finished collecting data click STOP, turn the hot plate off, record the pressure and temperature values in your data table. Examine your graph of pressure vs. temp. In order to determine if the relationship between pressure and temp is direct or inverse, you must use an absolute temp scale; that is, temp scale whose 0 degrees point corresponds to absolute zero. We will us the Kelvin absolute temp scale. Instead of manually adding 273 to each of the Celsius temps to obtain Kelvin values, you can create a new data column for Kelvin temp. For this, choose New Calculated Column from the Data menu, enter "Temp Kelvin" as the Name, "T Kelvin" as the short name, and "K" as the Unit. Enter the formula, select "Temperature" from the Variables list. Click the horizontal axis label and select "Temp Kelvin" to be displayed on the horizontal axis. Now decide if your graph of pressure vs. temp represents a direct or inverse relationship. First click the Curve Fit button, then choose mathematical relationship from the list at the lower left. If you think the relationship is linear, use Linear. If you think it is power, use Power. A best fit curve will be displayed on the graph. If you made the correct choice, the curve should match up well with the points. If the curve does not match up, try a different mathematical function and click the Try Fit button again. Autoscale both axes from zero by double-clicking in the center of the graph to view Graph Options. Click the Axis Options tab, and select Autoscale from 0 for both axes.


The volume and type of gas are kept constant in this lab. The gas pressure and temperature are directly related. Also, as the temperature increases, kinetic energy increases so gas molecules speed up and take up more space. If not more space is available, pressure will increase in order to compensate.


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The relationship between Lussac's Law is a direct mathematical relationship. The graph is linear as you can, and due to the direct relationship; pressure and temperature are proportional to each other.


independent variable- temperature (K)

dependent variable- pressure (kPa)

controlled variables- volume of gas, the mass, the nature of the gas

Example In Everyday Life

If a tire on a car were to explode, the heat from the tar would then cause the gases present in the tire to double; this would cause a pressurized tire. After some time passed, the tire would eventually pop or explode due to the pressure's buildup getting to such high amounts.
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If volume remains constant, the increase of temperature will also create an increase in pressure. Vice versa, if the temperature decreases, the pressure will decrease as well. Gay-Lussac's law is an ideal gas law where at constant volume; the pressure of an ideal gas is directly proportional to its absolute temperature. When completing this lab, we started with cold water, therefore; the temperature and pressure were low. When we used room temperature water, the temperature and pressure went up from the previous. And lastly, when we did hot water; the temperature and pressure were both high.