Question

When helium is allowed to expand into vacuum heating effect is observed. This is because (1) helium is a noble gas (2) the inversion temperature of helium is very low (3) helium is an ideal gas (4) the boiling point of helium is the lowest among the elements

Short answer

The inversion temperature of helium is very low. (Option 2)

Step-by-step solution

Identify key concept

Understand why a heating effect is observed when helium expands into a vacuum. The key concept here is related to the behavior of gases and the inversion temperature.

Understand the inversion temperature

The inversion temperature is the temperature at which a gas ceases to cool upon expansion and starts to heat up. For helium, this temperature is exceptionally low.

Relate to helium’s properties

Helium’s inversion temperature being very low leads to a heating effect when it expands because it is likely expand at a temperature higher than its inversion temperature.

Evaluate given options

Examine the provided options: (1) helium is a noble gas (2) the inversion temperature of helium is very low (3) helium is an ideal gas (4) the boiling point of helium is the lowest among the elements. Only option (2) directly relates to the heating effect due to expansion above its low inversion temperature.

Conclusion

Based on evaluation, select the most appropriate option which is (2) the inversion temperature of helium is very low.

Key concepts

Understanding Helium Properties

Helium is unique due to its distinct properties. It is a noble gas, meaning it rarely reacts with other elements. The atomic number of helium is 2, and it is the second lightest and second most abundant element in the universe. One remarkable property of helium is its exceptionally low boiling point of -268.9°C. This makes helium suitable for applications in cryogenics and superconducting magnets. Helium is also known for its low density and high thermal conductivity.

These properties mean that helium does not easily form compounds and remains in a gaseous state at extremely low temperatures. It is an ideal gas in many scenarios, but it's crucial to understand that its behavior changes at very low temperatures.

Exploring Gas Expansion

Gas expansion occurs when a gas moves from a region of higher pressure to a region of lower pressure. This can be observed, for instance, when a gas expands into a vacuum. During expansion, the gas molecules spread out to fill the available space. For most gases, expansion into a vacuum results in cooling, as predicted by the Joule-Thomson effect. However, helium behaves differently due to its unique properties.

The temperature and pressure during expansion play a critical role in determining whether the gas cools or heats up. For gases like helium, the inversion temperature—where the gas ceases to cool and starts to heat up—can be exceptionally low. When helium expands and reaches a temperature higher than its inversion temperature, it heats up instead of cooling.

Inversion Temperature and Thermodynamics

Thermodynamics studies energy, work, and heat within systems, particularly focusing on laws governing these exchanges. The inversion temperature is a term in thermodynamics describing the temperature at which a gas switches from cooling upon expansion to heating up. For helium, this temperature is very low, meaning it frequently encounters temperatures higher than its inversion temperature during expansion.

This behavior is closely related to the Joule-Thomson effect, which describes how the temperature of a real gas changes as it expands or contracts without performing work (i.e., in a vacuum). Most gases cool upon expansion; however, above their inversion temperature, gases like helium heat up. This is pivotal in understanding helium's behavior in various applications, especially those involving low temperatures and vacuum conditions.