Problem 83 - Chemistry The Science in Context

Question

Liquid helium boils at \(4.2 \mathrm{K}\). What is the boiling point of He in "C?

Step-by-Step Solution

Answer

Answer: The boiling point of liquid helium in Celsius is -268.95 °C.

Step 1: Write down the given temperature in Kelvin

We are given the boiling point of liquid helium as 4.2 K.

Step 2: Use the temperature conversion formula

To convert the temperature from Kelvin to Celsius, we will use the formula: Celsius temperature = Kelvin temperature - 273.15

Step 3: Substitute the given temperature in the formula

Now, let's substitute the given temperature in the formula: Celsius temperature = 4.2 - 273.15

Step 4: Calculate the Celsius temperature

By performing the calculation, we find the Celsius temperature: Celsius temperature = -268.95 °C So, the boiling point of liquid helium in Celsius is -268.95 °C.

Key Concepts

Temperature Conversion

Understanding temperature conversion is fundamental in fields like physics and chemistry, as various processes and properties are affected by temperature. Temperature conversion is necessary when we want to communicate or compare temperature readings in different units, such as from Kelvin (K) to Celsius (°C).

The Kelvin scale, a unit of absolute temperature, is crucial in the scientific world because it starts at absolute zero, the theoretically coldest temperature possible. Celsius, on the other hand, is widely used for everyday temperature measurements. Since these two scales have different starting points and increments, converting between them requires a simple formula.

Kelvin to Celsius Conversion

To convert temperature from Kelvin to Celsius, we utilize the formula: \( \text{°C} = K - 273.15 \). This equation considers the difference in zero points of the two scales. While water freezes at 273.15 K, it freezes at 0 °C. This 273.15 difference is what you subtract from a Kelvin temperature to convert it to Celsius.

Applying this to our liquid helium example, we see that the boiling point in Kelvin is 4.2 K. By subtracting 273.15, we obtain the Celsius equivalent of approximately -268.95 °C.

Practical Application

This conversion is not only academic but has practical applications in fields requiring precise temperature measurements, like cryogenics, where materials are studied at ultra-low temperatures.

Properties of Liquid Helium

Liquid helium is an exceptional substance with intriguing properties that are particularly evident at low temperatures. As the exercise indicates, helium transitions from a liquid to a gas at a mere 4.2 K. This boiling point is extremely close to absolute zero, highlighting liquid helium's use in cryogenics—for cooling superconducting magnets, for instance.

Superfluidity

One of helium's remarkable properties is superfluidity. When helium-4 is cooled to temperatures below 2.17 K, it enters a superfluid phase, exhibiting zero viscosity and the ability to flow without energy loss. This phase is characterized by peculiar behaviors such as creeping up and over the sides of a container.

Heat Capacity

Another important aspect is its heat capacity, which can absorb substantial heat with little temperature change, making it an excellent coolant. These properties make liquid helium vital in sectors like medical imaging and quantum computing, where maintaining extremely low temperatures is crucial.