gases

Question 1

Kinetic-Molecular Theory (KMT) of Gases Based on what three assumptions?

Answer 1

1. The gas consists of molecules of mass in ceaseless random motion, obeying the laws of classical mechanics
   – Particles move at constant velocity in straight lines between collisions (with other particles or container)
2. The size of the molecules is negligible (their diameters are much smaller than the average distance travelled between collisions)
3. Molecules interact only through brief elastic collisions

Question 2

RMS speed of the gas depends on the ______ of the gas, M, and the gas’s temperature (k)

Answer 2

molar mass

Question 3

_____ is one number that describes the speed of
molecules with given molar mass and temperature

Answer 3

𝑣𝑟𝑚𝑠

Question 4

For _____ temperatures and large masses, low speeds
predominate

Answer 4

low

Question 5

For ____ temperatures and small masses, the
distribution spreads out toward higher speeds

Answer 5

high

Question 6

If we know the average speeds of particles, we can figure out the average speed with which they
collide, called the _________

Answer 6

mean relative speed

Question 7

At constant V, Since 𝑣𝑟𝑒𝑙 ∝ 𝑣𝑚𝑒𝑎𝑛 ∝ 𝑣𝑟𝑚𝑠 ∝ 𝑇, collision frequency _______ with temperature

Answer 7

increases

Question 8

At constant T, the collision frequency is __________ to pressure

Answer 8

directly proportional

Question 9

At constant T, increasing N or decreasing V would ________ pressure, which would increase collision frequency

Answer 9

increase

Question 10

Collision frequency _______ with increasing T because the particles are moving faster

Answer 10

increases

Question 11

Collision frequency _________ with P because the particles are closer together and don’t need to move as far in order
to collide, thus causing more frequent collisions

Answer 11

increases

Question 12

If n is increased, P will ________ without changing T

Answer 12

increase

Question 13

If T is fixed but P goes up, 𝜆 will go down. P and 𝜆
are _______ proportional

Answer 13

Inversely

Question 14

𝜆 is ___________ of T

Answer 14

independent

Question 15

We know the ideal gas law is an approximation
that pretends that what?

Answer 15

1) gas particles do not interact except during collisions

2) gas particles
themselves have no volume

Question 16

Real gases behave most ideally when P is very _____
and/or T is very high

Answer 16

low

Question 17

When T is ______ (close to condensation) or P is high, gas behavior deviates significantly from ideality

Answer 17

low

Question 18

When gas particles are very close, they _____ each
other

Answer 18

repel

Question 19

When gas
particles are
close, but not
very close,
they ________
each other

Answer 19

attract

Question 20

Ideal gas particles, with no attractive interactions, would never form a ________ or solid

Answer 20

liquid

Question 21

Real gases

Answer 21

• Particles actually attract one another
  – Particles have non-neglible volume

Question 22

At large V and high T, the isotherms for real gases
are very similar to those of i____________

Answer 22

deal gases

Question 23

One correction is in terms of the volume (related to virial equation of state)

Answer 23

– Ideal gas law assumes particles occupy no volume
– vdW equation says particles do occupy volume, which
reduces the free volume particles can travel through
– b is the excluded volume per mole, so the free volume
becomes 𝑉 − 𝑛𝑏

Question 24

What does PEMDAS mean?

Answer 24

1. Parentheses
2. Exponentiation
3. Multiplication
4. Division
5. Addition
6. Subtraction

Question 25

The atom is an __________, spherical entity
composed of a positively charged central nucleus
surrounded by one or more negatively charged electrons.

Answer 25

electrically neutral

Question 26

The atomic nucleus consists of ________ and neutrons.

Answer 26

protons

Question 27

Charge

Answer 27

– Proton (+) and electron (–) have equal but opposite charges
– Neutron is electrically neutral (no charge)

Question 28

Mass

Answer 28

– Proton and neutron have very similar masses
– Electron has much smaller mass than proton or neutron

Question 29

Location

Answer 29

– Proton and neutron are in the nucleus
– Electrons are found outside the nucleus

Question 30

Atomic number (Z)

Answer 30

Number of protons in an atom’s nucleus

Question 31

Each element has a ________ atomic number

Answer 31

unique

Question 32

Atoms are neutral, so number of electrons is what?

Answer 32

equal to atomic number

Question 33

Mass number (A)

Answer 33

Sum of protons and neutrons in an atom’s nucleus

Question 34

________ are atoms of a given element with the same number of protons, but a different number of neutrons.

Answer 34

Isotopes

Question 35

Isotopes have the same atomic number, but a different _________

Answer 35

mass number

Question 36

Atomic mass is a weighted average of the mass numbers of ____________

Answer 36

all isotopes

Question 37

If the mean free path is written in as a combination equation with z then how does mean free path vary with pressure?

Answer 37

If n increased, P will increase without changing T

Question 38

If T is fixed but P goes up, mean free path (𝜆) will go __________

Answer 38

down

Question 39

To quantify the reduced pressure exerted by real gases we the _______

Answer 39

compression factor ( 𝑍 = 𝑉𝑚/
𝑉’𝑚) (Where 𝑉𝑚 is the molar volume (V/n) and 𝑉𝑚° is the molar volume of an ideal gas at same T and P)

Question 40

Using the Ideal gas law, what is another way to write the compression factor?

Answer 40

𝑍 = 𝑃𝑉𝑚/
𝑅𝑇 (or 𝑃𝑉𝑚 = 𝑅𝑇𝑍)

Question 41

What are the two ways of expressing the virial equation of state?

Answer 41

1. 𝑃𝑉𝑚 = 𝑅𝑇 1 + 𝐵′𝑃 + 𝐶′𝑃2 + ⋯)
2. 𝑃𝑉𝑚 = 𝑅𝑇 ( 1 + 𝐵/𝑉𝑚 + 𝐶/𝑉^2𝑚+ ⋯)

Question 42

The van der waals equation corrects the ideal gas law to replicate gas __________

Answer 42

behavior

Question 43

What is the first correction the van der waals equation makes?

Answer 43

1. is in terms of the volume
   – Ideal gas law assumes particles occupy no volume
   – vdW equation says particles do occupy volume, which
   reduces the free volume particles can travel through
   – b is the excluded volume per mole, so the free volume
   becomes 𝑉 − 𝑛𝑏

Question 44

What is the second correction the van der waals equation makes?

Answer 44

is in terms of the pressure
– Ideal gas law assumes particles don’t interact
– However, they actually attract each other, which
* Means collisions with container walls are less frequent
* The force of collisions is also reduced
* The strength of this reduction in frequency and force is
proportional to molar concentration, n/V
* Because both frequency and force are each reduced by a factor
proportional to n/V, the n/V term is squared
* The sign in front of this term is negative, since the attraction
reduces pressure
* 𝑎 is the proportionality constant for this pressure reduction

Question 45

van der Waals equation is based on the ideal gas
law but incorporates a correction for ________
and a correction for __________

Answer 45

pressure, volume

Question 46

Note that the vdW equation does not perfectly
represent the behavior of real gases but it does
display __________

Answer 46

general behavior

Question 47

Isotherms produced by vdW eq’n are same as ideal gas
law for _______ temperatures and low ________

Answer 47

high, molar volumes

Question 48

Liquids and gases coexist when attractive and repulsive
effects are in _______

Answer 48

balance (related to vdW eq)

Question 49

Can find the compression factor for critical points by plugging in the _________

Answer 49

critical constants