Helium (He) and xenon (Xe) gases are each held at 400 K in separate containers at the…
CHEMISTRY · Multi-part · AP · Chemistry · Properties of Substances and Mixtures · Properties of Substances and Mixtures
Problem
Helium (He) and xenon (Xe) gases are each held at 400 K in separate containers at the same pressure. A Maxwell–Boltzmann distribution of molecular kinetic energies is conceptually sketched for each gas on identical axes.
Consider a threshold kinetic energy of 5.0 kJ mol−1.
(a) Compare the average kinetic energies of individual He and Xe atoms at 400 K. Explain your reasoning.
(b) Determine whether the fraction of atoms with energies ≥ 5.0 kJ mol−1 is greater for He, greater for Xe, or approximately the same for the two gases. Provide a justification based on features of their respective energy distributions.
(c) Suppose instead that the threshold is expressed in terms of molecular speed rather than energy. Predict qualitatively how the comparison in part (b) would change, and explain why.