Temperature & Gases 1.2

Question 1

List 5 old state variables

List 3 newly introduced state variables

Answer 1

1) Volume, pressure, mass, mass density, thermal energy

2) Moles, number density, temperature

Question 2

What is thermal equilibrium

Answer 2

When all state variables have settled and are constant

Question 3

What does the “~” symbol mean? e.g ~10

Answer 3

“Known to within a factor of…” eg(Known to within a factor of 10)

Question 4

What is the equation for Number Density

What is the approximate number density for Solids and Gases?

Answer 4

N/V (m^-3)
Solids ~ 10^29 m^-3
Gas < 10^27 m^-3

Question 5

What constitutes the atomic mass number?

Answer 5

A = #protons + #neutrons

Question 6

Describe the atomic mass scale

Answer 6

All masses are defined as relative to 12C.
Carbon: 12:12 has 12amu
Hydrogen: 1:12 has 1amu

Question 7

List the 3 equations relating mols, mass, and atoms.
n: mols
N: particles
Na: Avocado's number
M: Mass of system
m: mass of atoms

Answer 7

n = N/Na
N = M/m
n = M/Mols

Eh this is kinda trash without subscripts…

Question 8

Describe the origin story of the Celsius scale

Answer 8

in 1742, Anders Celsius sealed mercury in a capillary tube and observed how it moved up and down relative to temperature. He measured the freezing point and boiling point of water, and marked 100 equal ticks between them, which is why the scale is also called “Centigrade”

Question 9

What equation converts Celsius to Farenheit

I guess converting from Farenheit to Celsius is more important. Do that instead.

Answer 9

Tf = (9/5)Tc + 32

Tc = (Tf - 32)(5/9)

Question 10

List 4 different types of thermometers

Answer 10

• Glass tube thermometer (filled with Hg or alcohol)
• Bimetallic strips
• Thermocouples (Generate voltage depending on tmp)
• Constant Volume gas thermometer

Question 11

Describe the basis of the idea of Absolute Zero

Answer 11

When different gases are measured in constant volume thermometers, the relationship between temperature and measured pressure is linear. And all gases extrapolate to 0Pa at T = -273C

Question 12

Describe:
Critical point
Triple Point
Phase Equilibrium

Answer 12

1) Boundary between phase changes
2) Where phase boundaries meet
3) A temperature where any amount of any phase can happily co-exist

Question 13

Fun facts:
What is average Fridge Freezer Temp?
What is the idea behind pressure cookers?

Answer 13

1) Freezers are ~= -20C
2) Pressure cookers trap steam inside, allowing pressure in vessel to build. According to the phase diagram of water, the boiling point of water increases as pressure increases, allowing the food to boil at temperatures higher than 100C

Question 14

Who originally conceived the idea of atoms?

Answer 14

Leucippus & Democrius
440-420 BCE
based on the greek word “atmos” meaning “indivisible

Idea was revived by Daniel Bernoulli in 1740
But wasn’t accepteed for nearly a century

Question 15

What forces in atoms correspond to a material’s overall strength?

Answer 15

Attractive Force: Tensile Strength

Repulsive Force: Compressive Strength

Question 16

Describe the ideal gas model, and its two constraints

Answer 16

All gas molecules are hard spheres that only interact when in contact BoING BOINg

1) Must be Low Density: At higher densities, the attractive forces have a greater influence
2) Temperature Must be well above condensation point

Question 17

Describe the Ideal Gas Law

Answer 17

For ALL GASES, the relationship between pV and nT is a linear graph with slope R=8.31J/mol*K

pV = nRT R = 8.31J/mol*K

Question 18

Derive the equation for ideal gases in a sealed container

Answer 18

pV/T = nR = constant

pfVf/Tf = piVi/Ti

Question 19

Derive the equation for the molecular ideal gas law gas law

Also rearrange it to solve for number density

Answer 19

To convert moles to molecules, divide by Avocado’s number! Resulting in the Boltzman constant!
Kb = R/Na = 1.38^-23J/K

pV = NKbT

N/V = P/KbT