Liquid nitrogen boils at -195.8 °C. Express the boiling point of liquid nitrogen in Kelvin.
A) -77.4 K
B) 77.4 K
C) on the Kelvin scale, all temperatures are 0 K
D) -469.0 K
E) 469.0 K
The Correct Answer and Explanation is:
The correct answer is: B) 77.4 K
To convert temperatures from degrees Celsius (°C) to Kelvin (K), you use the following formula: K=°C+273.15K = °C + 273.15
This conversion is based on the definition of the Kelvin scale, which starts at absolute zero (0 K), the point at which all molecular motion theoretically stops. Absolute zero corresponds to -273.15 °C. The Kelvin scale is commonly used in scientific contexts because it is an absolute temperature scale, meaning it does not use negative numbers for thermal energy.
Let’s apply the formula to the boiling point of liquid nitrogen: K=−195.8+273.15=77.35≈77.4 KK = -195.8 + 273.15 = 77.35 \approx 77.4 \, \text{K}
So, the boiling point of liquid nitrogen is 77.4 K, making option B the correct answer.
Why the Other Choices Are Incorrect:
- A) -77.4 K: Incorrect. Kelvin temperatures are never negative because 0 K is the lowest possible temperature. You cannot have a temperature below absolute zero.
- C) On the Kelvin scale, all temperatures are 0 K: Incorrect. While 0 K is the lowest possible temperature (absolute zero), the Kelvin scale includes a wide range of temperatures above this point. For example, room temperature is about 293 K.
- D) -469.0 K: Incorrect. Again, Kelvin cannot be negative. Also, this is a confusing number—perhaps referencing -469°F, which is closer to absolute zero in Fahrenheit.
- E) 469.0 K: Incorrect. This is far too high for the boiling point of liquid nitrogen. In fact, 469 K is about 195.9 °C above the freezing point of water.
Conclusion:
Understanding temperature scales is essential in scientific work. The Kelvin scale offers a practical and absolute measure of temperature that aligns with the laws of thermodynamics. Liquid nitrogen’s boiling point of 77.4 K is a key example of applying this scale correctly.
