States of Matter 1.11: Absolute Zero Wiva k12 Chemistry

1745

Andrus Celsius's temperature scale is adopted a year after his death.

1724

Daniel Gabriel Fahrenheit develops a temperature scale.

Temperature is a measure of the average kinetic energy of the molecules in a system.

If you measure the KE of a group of runners and divide by the number you measured, you will come up with the average KE for the runners. With systems of atoms and molecules, you can do much the same thing: You can find the average KE of the particles in the system. The average kinetic energy of a system is called by a specific name: temperature. Temperature, no matter what scale you use, is a measure of the average kinetic energy of the particles in the system.

Motions of gas molecules account for the properties of gases.

In an ideal gas, the particles are in constant random motion. The particles collide with one another and with the walls of the container. The motions of these particles account for the properties of gases. -Pressure: the combined forces of the collisions between the particles and the walls of the container; the more motion, the more collisions, and the greater the pressure -Volume: the moving molecules create space; the more motion, the farther the distance between molecules, and the greater the volume -Temperature: the measure of molecular motion

Use these formulas to convert temperatures between degrees Celsius and kelvins.

In the laboratory, temperatures are often measured in degrees Celsius and then converted to kelvins. The formula for this conversion is K = °C + 273.15. However, it is usually rounded to K = °C + 273 To go from the Kelvin scale to the Celsius scale, use this formula: °C = K - 273 So a temperature of 300 K in degrees Celsius would be °C = K - 273 = (300 - 273) = 27°C Examine the examples provided and note that the degree sign is never used when writing kelvins.

Things in motion have kinetic energy.

Kinetic energy, or KE, is the energy of any mass that has velocity—from an atom to a planet. Gas molecules move, of course, so each has its own kinetic energy. When you heat a gas, the KE of molecules goes up because each molecule moves faster. Each molecule has a greater velocity. When you cool a gas, the KE of each molecule goes down because each molecule has a lower velocity.

1848

Lord Kelvin develops a temperature scale based on absolute zero.

Lord Kelvin introduced absolute zero.

Making use of theories of kinetic energy and molecular motion, British physicist William Thomson (Lord Kelvin) introduced the concept of absolute zero. Temperature is a measure of the average kinetic energy of molecules in a gas. When average kinetic energy increases, we say the temperature goes up. And when average kinetic energy decreases, we say the temperature goes down. Using a thermometer of any scale, we can state how much it goes up or down. Kelvin reasoned that there must be a temperature at which average kinetic energy is zero and all motion stops. He called this temperature absolute zero. Nothing can be colder than absolute zero because temperature is a measure of motion, and all motion (atomic, molecular) ceases at absolute zero. Absolute zero is one of the reference points used in the absolute temperature scale.

Absolute zero is the measure of the average kinetic energy of motionless molecules.

Molecular motion accounts for the properties of gases. Molecules move, and thus they have kinetic energy (KE). Heating or cooling gases adds or removes energy and changes a molecule's KE. Temperature is a measure of the average kinetic energy of the molecules. All molecular motion stops at absolute zero (0 K), and nothing can be colder. Absolute temperature is measured in kelvins. The physical properties of substances at low temperatures have interesting applications.

The Kelvin scale is used for measuring temperature.

The Kelvin scale of temperature started with two reference points. Initially, the reference points were absolute zero (0 K) and the freezing point of water (273.15 K). At that time, the absolute temperature was defined as kelvins, not degrees Kelvin. Notice that the word kelvin is spelled with a small k. However the symbol for a kelvin is a capital K. When you read absolute temperature in a book or problem, it means temperature measured on the Kelvin scale.

The concept of absolute zero is a result of the study of the behavior of gases.

The study of gases and steam engines in the nineteenth century led to the modern ideas of heat and kinetic energy. From these ideas, thermometers and temperature scales were developed. William Thomson, called Lord Kelvin, developed the concept of absolute zero. In this lesson, you will learn about the Kelvin scale, molecular motion, kinetic energy, and absolute zero.

Now review some model problems.

Turn to Problem Set 57, Absolute Zero, in the Chemistry: Problems and Solutions book. Review the sample problems and complete problems 3-5. When you have finished, check your answers in the Solution Key.

Why do scientists try to reach absolute zero?

Very interesting things happen to matter at low temperatures. For example, when certain materials are cooled to near absolute zero, their electrical resistance almost disappears. These materials, such as metals, alloys, and other compounds, are called superconductors, and they can be used to make powerful electromagnets that produce little or no heat and consume little electricity. Such magnets can be used in particle accelerators that are used to smash atoms and explore the structure of subatomic particles like the proton and the neutron, or the energies that hold the nucleus together. To get near absolute zero, scientists use a cascade cooling process that repeats pressurizing, evaporating, and cooling various gases in sequence. Scientists have come within a billionth of a kelvin of absolute zero.

How cold is absolute zero?

You are probably most familiar with temperatures such as the freezing point of water or the boiling point of water. The average surface temperature of the earth is 15°C, or 288 K. These temperatures are well above absolute zero. Many gases condense to liquid at low temperatures. For example, liquid hydrogen and liquid oxygen, which are the fuels for the space shuttle, boil at 20.3 K and 90.2 K, respectively.

Absolute Zero

a temperature of 0 K, at which all atomic motion ceases

Kelvins

a unit on the Kelvin scale and a measure of temperature

At 52°C, the pressure inside a gas-filled container is 467 kPa. What is the absolute temperature of the gas? a.) 163 K b.) 325 K c.) 335 K d.) 651 K

b.) 325 K

Look at the diagram and choose the statement that is true at room temperature if both systems are at the same pressure and volume. a.) The temperature of the system in curve A is greater than the temperature of the system in curve B. b.) The temperature of the system in curve B is greater than the temperature of the system in curve A. c.) The temperature of the system in curve A is equal to the temperature of the system in curve B.

b.) The temperature of the system in curve B is greater than the temperature of the system in curve A.

At which of the following temperatures does all molecular motion stop? a.) 0 R b.) 0*C c.) 0 K d.) 0*F

c.) 0 K

You have 0.5 L of air at a pressure of 203 kPa and 70°C in a rigid, sealed container. What is the absolute temperature of the air? a.) 70 K b.) 70 K c.) 203 K d.) 273 K

c.) 203 K

At which of the following temperatures is the average kinetic energy of the molecules in one liter of nitrogen gas greatest? a.) 40°C b.) 273 K c.) 310 K d.) 60°C

d.) 60°C

Kinetic Energy

energy associated with the movement of any mass