a. Molecules in random motion
b. Gas molecules infinitely small points
c. Molecules move in straight lines until they collide
d. Molecules don’t interact with each other
e. All collisions are elastic
f. **a,c,e are mostly true. B,d not.
2. Pressure=arises from force exerted on walls by particles.
a. See derivation for total pressure exerted by gas in notebook.
3. The internal energy U of ideal gas is a function of T only for ideal gases
a. U=Utrans + Urot + Uvib + Uoth. The first three are functions of temperature only.
c. At normal temperatures around 300K, we know from our derivations that:
i. Utrans=3/2nRT where n is the number of moles. Before in our derivation,
we only had RT since we stated n as 1 mol.
4. Internal energy U
a. Utrans has energy levels very close together, so don’t need high T to jump to
next energy level
b. Urot has larger energy gaps, so require higher temperatures
i. For non linear: Urot=3/2nRT
ii. For linear: Urot=nRT since it only has 2 degrees of freedom for rotation
instead of 3.
c. Uvib has even larger energy gaps, so it is around 0 for small diatomic molecules
at normal temperatures.
i. Each vibrational df contributes RT to total internal energy
5. Interestingly, in an ideal gas we only have 1 type of internal energy: Utrans since we
assume gas particles are infinitely small and thus cannot rotate or v