Quiz 1

Question 1

What’s different between macroscopic objects and a single particle?

Answer 1

Single particles physics are time reversal invariant. Macroscopic processes are often irreversible.

Question 2

What is thermodynamic equilibrium?

Answer 2

No observable rearrangement of macroscopic:
Energy (thermal equilibrium)
Volume (mechanical equilibrium)
Particles (diffuse equilibrium)

Question 3

0th law of thermodynamics

Answer 3

A well defined quantity called temperature exists such that two systems will be in thermal equilibrium iff both have the same temperature.

Question 4

What is the ideal gas model?

Answer 4

1. All molecules identical, N huge
2. Molecules tiny compared to avg separation
3. Neglect potential energy
4. Molecules obey N 3rd law & motion random
5. Collisions between molecules and container walls are elastic

Question 5

Ideal gas law

Answer 5

PV=NkT

Question 6

Avg translational kinetic energy of a molecule in terms of temperature

Answer 6

= (3/2)kT

Question 7

True or false: temperature requires collision of particles

Answer 7

False. Temperature is proportional to KE, but because of the assumption of elasticity, KE will not change with the introduction of collisions.

Question 8

True or false: pressure in an ideal gas requires collisions

Answer 8

False. Pressure arises from the force of particles hitting the walls. That isn’t changed whether there are collisions or not.

Question 9

Which particles in the atmosphere have more translational KE, N2 or O2? What about velocity?

Answer 9

They have the same KE at a given temperature. N2 has higher velocity.

Question 10

How is U_thermal different from E_total?

Answer 10

1. Microscopic KE dominates
2. PE is often neglected
3. Translation of the system is ignored.

Question 11

True or false: the # of d.o.f in particles of an ideal gas is always 3.

Answer 11

False. We still treat diatomic molecules such as N2 as ideal gas particles.

Question 12

How many d.o.f. does a diatomic molecule have?

Answer 12

5: 3 translational and 2 rotational

Question 13

What is a degree of freedom?

Answer 13

A way in which energy can be stored quadratically in particles

Question 14

How many d.o.f. in a simple harmonic oscillator?

Answer 14

2: 1 KE and 1 PE term

Question 15

If you add more molecules to a system that contains the same type of molecule, do you keep the original degrees of freedom?

Answer 15

Yes: f is the degrees of freedom per particle.

Question 16

Degrees of freedom in 1 mol of solid iron

Answer 16

6: 0 translational, 0 rotational, 6 vibrational (can oscillate in three directions*2)

Question 17

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?

Answer 17

They have the same average translational kinetic energy. So they have the same average velocity

Question 18

Define heat

Answer 18

The spontaneous flow of energy from one system to another as a result of temperature difference between the two systems.

Question 19

What are the three forms of energy transfer in heat?

Answer 19

Radiation: EM
Conduction: surface contact between two systems
Convection: flow of molecules past a surface

Question 20

What does the sign of heat, Q, mean?

Answer 20

Positive: heat flows in (energy increases) and
Negative: heat flows out (energy decreases)

Question 21

What is work (in the context of thermal physics)?

Answer 21

All other forms of energy transfer besides heat

Question 22

What is the relationship between the work done on a system and the work done by a system?

Answer 22

W_on a system = - W_by a system

Question 23

What does the sign of the work done on a system (W) mean for delta U?

Answer 23

Positive W means delta U is positive.