Name: kelvin temperature and gas thermometer standards
Uploaded: 2023-04-30T12:29:16.000Z
Duration: 1 min 22 s
Channel: JoVE

K12 Standards

Texas Essential Knowledge and Skills

High School

Chemistry

CHEM.13

CHEM.13.D

Gas Thermometers and the Kelvin Scale

Ein Gasthermometer bewertet die Temperatur anhand von Änderungen des Drucks oder des Volumens des eingefüllten Gases.
Es gibt zwei Arten von Gasthermometern: Konstantes Volumen und Konstantdruck, und das Gasthermometer mit konstantem Volumen ist das am weitesten verbreitete.
Das Prinzip dieses Thermometers besteht darin, dass bei konstantem Volumen der Druck eines Gases mit steigender Temperatur zunimmt.
Zur Kalibrierung des Gasthermometers wird der Druck bei 0 und 100 Grad Celsius gemessen.
Diese Werte werden in einer geraden Linie dargestellt, die extrapoliert wird, um die Nulldrucktemperatur zu ermitteln.
Diese Temperatur ist der Nullpunkt der Kelvin-Skala. Dies ist die Standardskala für die Temperatur, da die SI-Einheit der Temperatur Kelvin ist.
Der absolute Nullpunkt ist die niedrigstmögliche Temperatur, die im Idealfall die völlige Abwesenheit von thermischer Energie widerspiegelt.
Auf der Kelvin-Skala liegt der Gefrierpunkt von Wasser bei 273,15, während der Siedepunkt bei 373,15 liegt. Der Unterschied ist derselbe wie auf der Celsius-Skala; Nur der Nullpunkt ist anders.
So lässt sich die Beziehung zwischen Kelvin- und Celsius-Skala leicht feststellen.

<ol>
	<li>OpenStax. (2019). Universitätsphysik Vol. 2. [Webversion]. Abgerufen von <a href="https://openstax.org/books/university-physics-volume-2/pages/1-2-thermometers-and-temperature-scales">https://openstax.org/books/university-physics-volume-2/pages/1-2-thermometers-and-temperature-scales</a></li>
</ol>

gas-thermometer und die kelvin-skala

Die Definition von Temperatur in Bezug auf die Bewegung von Molekülen legt nahe, dass es eine niedrigste mögliche Temperatur geben sollte, bei der die durchschnittliche kinetische Energie der Moleküle null ist (oder das Minimum, das durch die Quantenmechanik erlaubt ist). Experimente bestätigen die Existenz einer solchen Temperatur, die absolute Null genannt wird. Eine absolute Temperaturskala ist eine, deren Nullpunkt absolute Null ist. Solche Skalen sind in der Wissenschaft praktisch, da mehrere physikalische Größen, wie das Volumen eines idealen Gases, direkt mit der absoluten Temperatur zusammenhängen.

Die Kelvin-Skala ist die absolute Temperaturskala, die in der Wissenschaft üblicherweise verwendet wird.

Die Kelvin-Skala ist Teil des SI-Einheitensystems, daher ist ihre tatsächliche Definition komplizierter als die oben genannte. Zunächst wird sie nicht in Bezug auf den Gefrier- und Siedepunkt von Wasser definiert, sondern in Bezug auf den Tripelpunkt. Der Tripelpunkt ist die einzigartige Kombination aus Temperatur und Druck, bei der Eis, flüssiges Wasser und Wasserdampf stabil koexistieren können. Die Temperatur des Tripelpunkts ist als 273,16 K definiert. Diese Definition hat den Vorteil, dass die Gefriertemperatur und Siedetemperatur von Wasser zwar vom Druck abhängen, es aber nur eine Tripelpunkt-Temperatur gibt.

Auch bei klar definierten Punkten auf der Skala geben unterschiedliche Thermometer etwas unterschiedliche Ergebnisse für andere Temperaturen. Daher ist ein Standardthermometer erforderlich. Metrologen haben zu diesem Zweck das Gas-Thermometer mit konstantem Volumen gewählt. Ein Gefäß mit konstantem Volumen, das mit Gas gefüllt ist, wird Temperaturänderungen ausgesetzt, und die gemessene Temperatur ist proportional zur Druckänderung. Die Ergebnisse hängen etwas von der Wahl des Gases ab, aber je geringer die Dichte des Gases im Kolben ist, desto besser stimmen die Ergebnisse für verschiedene Gase überein. Wenn die Ergebnisse auf null Dichte extrapoliert werden, stimmen die Ergebnisse sehr gut überein, wobei null Druck einer Temperatur von absoluter Null entspricht. Gas-Thermometer mit konstantem Volumen sind groß und erreichen langsam das Gleichgewicht, daher werden sie hauptsächlich als Standards zur Kalibrierung anderer Thermometer verwendet.

Gas-Thermometer und die Kelvin-Skala

Die Definition der Temperatur in Bezug auf die molekulare Bewegung legt nahe, dass es eine möglichst niedrige Temperatur geben sollte, bei der die durchschnittliche kinetische Energie ...

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kelvin temperature and gas thermometer standards

Kelvin temperature is the absolute scale used in science, and it starts at absolute zero. That zero point matches the lowest possible temperature, where molecular motion reaches zero or the minimum allowed by quantum mechanics. Scientists use this scale because some physical quantities, such as the volume of an ideal gas, depend directly on absolute temperature.

The Kelvin scale is part of the SI system of units, so its definition is more precise than simply using water’s freezing and boiling points. Instead, it is tied to the triple point of water. The triple point is the only temperature and pressure combination where ice, liquid water, and water vapor can all coexist. Its temperature is defined as 273.16 K, which is useful because it does not change with pressure the way water’s freezing and boiling points do.

Even with fixed reference points, different thermometers can give slightly different readings for other temperatures. For that reason, scientists need a standard thermometer. Metrologists use the constant-volume gas thermometer for this job. In this device, a gas in a sealed vessel stays at the same volume while temperature changes, and the temperature is found from the change in pressure.

The choice of gas can affect the results a little. However, the less dense the gas in the bulb, the better different gases agree. When the results are extrapolated to zero density, they match well, and zero pressure corresponds to absolute zero. Constant-volume gas thermometers are large and slow to reach equilibrium, so they are mainly used as standards to calibrate other thermometers.

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Kelvin Temperature and Gas Thermometer Standards

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