Quiz 1 Flashcards
What’s different between macroscopic objects and a single particle?
Single particles physics are time reversal invariant. Macroscopic processes are often irreversible.
What is thermodynamic equilibrium?
No observable rearrangement of macroscopic:
Energy (thermal equilibrium)
Volume (mechanical equilibrium)
Particles (diffuse equilibrium)
0th law of thermodynamics
A well defined quantity called temperature exists such that two systems will be in thermal equilibrium iff both have the same temperature.
What is the ideal gas model?
- All molecules identical, N huge
- Molecules tiny compared to avg separation
- Neglect potential energy
- Molecules obey N 3rd law & motion random
- Collisions between molecules and container walls are elastic
Ideal gas law
PV=NkT
Avg translational kinetic energy of a molecule in terms of temperature
= (3/2)kT
True or false: temperature requires collision of particles
False. Temperature is proportional to KE, but because of the assumption of elasticity, KE will not change with the introduction of collisions.
True or false: pressure in an ideal gas requires collisions
False. Pressure arises from the force of particles hitting the walls. That isn’t changed whether there are collisions or not.
Which particles in the atmosphere have more translational KE, N2 or O2? What about velocity?
They have the same KE at a given temperature. N2 has higher velocity.
How is U_thermal different from E_total?
- Microscopic KE dominates
- PE is often neglected
- Translation of the system is ignored.
True or false: the # of d.o.f in particles of an ideal gas is always 3.
False. We still treat diatomic molecules such as N2 as ideal gas particles.
How many d.o.f. does a diatomic molecule have?
5: 3 translational and 2 rotational
What is a degree of freedom?
A way in which energy can be stored quadratically in particles
How many d.o.f. in a simple harmonic oscillator?
2: 1 KE and 1 PE term
If you add more molecules to a system that contains the same type of molecule, do you keep the original degrees of freedom?
Yes: f is the degrees of freedom per particle.
Degrees of freedom in 1 mol of solid iron
6: 0 translational, 0 rotational, 6 vibrational (can oscillate in three directions*2)
CO2 and Ar have nearly the same mass. Assuming they did have the same mass, at some given temperature, which would have higher average velocity?
They have the same average translational kinetic energy. So they have the same average velocity
Define heat
The spontaneous flow of energy from one system to another as a result of temperature difference between the two systems.
What are the three forms of energy transfer in heat?
Radiation: EM
Conduction: surface contact between two systems
Convection: flow of molecules past a surface
What does the sign of heat, Q, mean?
Positive: heat flows in (energy increases) and
Negative: heat flows out (energy decreases)
What is work (in the context of thermal physics)?
All other forms of energy transfer besides heat
What is the relationship between the work done on a system and the work done by a system?
W_on a system = - W_by a system
What does the sign of the work done on a system (W) mean for delta U?
Positive W means delta U is positive.
