Free Absolute Zero MCQs with Answers

1. Charles's law predicts that a gas cooled at constant pressure would reach zero volume at

• A. 0 degrees C
• B. -100 degrees C
• C. -273.15 degrees C
• D. -373 degrees C

Explanation: Extrapolating the straight line of volume against temperature backwards, every gas reaches zero volume at minus 273.15 degrees Celsius, which is defined as absolute zero or 0 K. The extrapolation is theoretical, since every real gas liquefies well before that point. This is precisely why the Kelvin scale exists and why gas law calculations must use it.

2. Absolute zero is the temperature at which

• A. the volume of an ideal gas extrapolates to zero
• B. water freezes
• C. all gases liquefy
• D. pressure becomes infinite

Explanation: Extending the straight line of a volume against temperature graph backwards, it meets the axis at minus 273.15 degrees Celsius, which is defined as zero kelvin. No real gas actually reaches this point, since every gas liquefies first, so the zero volume is an extrapolation rather than an observation. It is the lowest temperature theoretically attainable.

3. Which of the following is true about pressure for an ideal gas at -273 degrees Celsius?

• A. P = 1 atm
• B. P = 2 atm
• C. P = 3 atm
• D. P = 0 atm

Explanation: Absolute zero is minus 273 degrees Celsius, and extrapolating a pressure against temperature graph for a fixed volume of ideal gas back to that point gives zero pressure, since molecular motion reaches its minimum and no collisions occur with the walls. No real gas actually reaches this, because every gas liquefies first, so the value is an extrapolation rather than an observation. It is exactly how the absolute scale is defined.