Helium gas in a sealed container is initially at 400 K
CHEMISTRY · Multi-part · AP · Chemistry · Properties of Substances and Mixtures · Properties of Substances and Mixtures
Problem
Helium gas in a sealed container is initially at 400 K. At this temperature the most probable molecular speed is measured to be 1.25 × 10³ m s⁻¹. The container is then heated to 800 K while the volume is adjusted to keep the pressure constant.
Answer the following questions about the molecular-speed distribution before and after the temperature change.
(1) Estimate the new most probable speed of a helium atom at 800 K. Show your reasoning clearly.
(2) Describe how the shape of the molecular-speed distribution changes when the temperature is increased from 400 K to 800 K. In your description, comment on both the peak height and the spread of speeds.
(3) Does the average kinetic energy of the helium atoms exactly double when the temperature is raised from 400 K to 800 K? Provide a quantitative justification for your answer.