Absolute Zero Device

Introduction

The Absolute Zero Device is a large, working classroom model for studying the relationship between temperature and pressure of a confirmed volume of gas. By taking pressure readings at various equilibrium temperatures, this relationship can be plotted on a graph. Since an ideal gas ceases to demonstrate any pressure at absolute zero, absolute zero can be determined by extrapolating the plotted data.

Concepts

• Absolute zero
• Pressure
• Temperature

Materials

Safety Precautions

Never pressurize the system beyond the maximum rating of the pressure gauge. The pressure gauge is the most sensitive instrument of the Absolute Zero Device. Pressurizing the gauge beyond the 30-psi (2.0-bar) limit risks destroying the inner parts of the gauge. Over-pressurizing the gauge (also referred to as “clocking the gauge”) will void any warranty and will cause irreversible damage to the gauge. Take care to prevent percussive damage. Do not drop the apparatus or allow rough treatment of the gauge. Never dismantle any part of the apparatus while the system is pressurized. If disassembled, component parts may be a choking hazard. This apparatus is NOT A TOY and is for science education. Operation should be limited to a qualified teacher.

Dry ice is extremely cold and may cause frostbite. Handle only with insulated or heavy cloth gloves and never with wet hands. The demonstrator and all observers must wear chemical splash goggles.

Procedure

The unit consists of a large, easy-to-read pressure gauge and a stainless steel bulb interconnected by a tube. Located perpendicular to the tube and near the gauge end of the unit is an air valve and a handle. The pressure gauge reads pressure in two scales. PSI: Pounds per square inch with a range from 0 to 30 psi. BAR: A bar equals 100 x kPa. The scale has a range from 0 to 2.0 bar.

The pressure of a confined gas varies as a function of the temperature. The bulb of the device will be subjected to different temperatures and the resulting pressures will be read on the gauge. Record the various temperatures and the correlating pressure reading in a two-column table labeled temperature and pressure. Graph temperature on the horizontal (x) axis and the pressure data the vertical (y) axis. When setting up the graph, allow that the temperature range extends to at least –300 °C.

1. In each of the 2-liter beakers, prepare one of the following: a. Boiling water b. Ice/water mixture c. Dry ice/acetone mixture
2. Open the valve to equalize the pressure. The first set of data to be recorded can be ambient pressure at room temperature.
3. Immerse the bulb in the boiling water. Use the support stand and clamp to secure the device. Allow the pressure to reach equilibrium. Record the temperature and pressure readings.
4. Immerse the bulb in the ice/water mixture. Allow the pressure to reach equilibrium. Record the temperature and pressure readings.
5. Immerse the bulb in the dry ice/acetone mixture. Allow the pressure to reach equilibrium. Record the temperature and pressure readings.
6. Create a graph with temperature along the horizontal (x) axis and pressure along the vertical (y) axis.
7. Plot the obtained data on this graph.
8. Draw a “best-fit” line through the data points and extrapolate the line formed on the graph to the point at which pressure would equal zero. The corresponding temperature at this point is an approximation of absolute zero in degrees celsius.

Teacher Tips

• Flinn Catalog No. TC1523, thermocouple sensor, has a temperature range of –200 °C to 1400 °C. A computer interface such as TC1559, LabQuest™ Mini is required. Alternately, four or more water baths may be set up from a high temperature of boiling water to a low temperature of ice water, and at least two other temperatures between 0 and 100 degrees C (hot water and room temperature, for example). A salt/ice water bath may also be used to achieve a temperature below 0 °C (some sources report –20 °C can be reached with a 1 to 3 ratio by weight of sodium chloride to ice). With four or five data points, a reasonably accurate graph may be drawn and extrapolated to absolute zero.

Discussion

Gay-Lussac’s Law

Joseph Louis Gay-Lussac (1778–1850) systemically and mathematically studied temperature and its effect on the pressure and temperature of gases. Gay-Lussac published the relationship between the pressure and temperature of a gas. Today this law, commonly referred to as Gay-Lussac’s Law, states that the pressure of a fixed mass and fixed volume of a gas is directly propor-tional to the temperature of the gas in Kelvins. This law can be expressed mathematically as P ∝ T or by Equation 1 for the ini¬tial and final conditions.

Approximating Absolute Zero

Absolute zero is the temperature at which all thermodynamic motion stops. Absolute zero, like an ideal gas, is unobtainable in nature. However, knowing its definition allows us to approximate it fairly easily. The pressure that a gas exerts on the walls of a closed container is the cumulative result of individual collisions between gas molecules and each other, and gas molecules with the walls of the container.

When the temperature of a gas is raised, the energy of these collisions increases, and the pressure on the walls of the container subsequently rises. Similarly, when the temperature of a gas is decreased, the energy of the collisions is reduced, and the pressure is also reduced.

When all the energy is taken out of the system (reduce the thermodynamic temperature of the system to zero), the collisions of the molecules with each other cease, as do the collisions between the molecules and the sides of the container. The pressure on the walls of the container will cease as well. When all the energy is taken out of a system, we say that the system has reached absolute zero. At absolute zero, such a system will theoretically exhibit no gas pressure whatsoever. By extrapolating the graph created in the experiment stage to zero pressure, we can approximate absolute zero temperature.