PHYSICS · Multi-part · Fermi University Physics · Thermal, Statistical & Complex Systems · Kinetic theory and transport in gases · Kinetic theory and transport in gases
Thermal Physics, Ch Temperature, pressure and the kinetic theory of gases
Problem
A water molecule is bent, not linear: its three atoms do not lie on one line, so it can rotate about three independent axes, each rotation storing energy as a quadratic term. Take the molecule to be rigid, so that its vibrations are inactive, and treat steam as an ideal gas.
((a)) Count the quadratic degrees of freedom of a rigid water molecule and predict the molar energy per kelvin needed to warm steam at fixed volume.
((b)) The measured molar heat capacity of steam at constant volume near 373K is about 25.8JK−1mol−1. Compare it with the value predicted in (a) and say what the difference suggests. Use R=8.314JK−1mol−1.