Kinetic Theory (unit 3)

Question 1

Equation of states for ideal gas?

Answer 1

Pv =nRT or NkT

Question 2

What is R in the equation?

Answer 2

molar gas constant

Question 3

What is K in the equation?

Answer 3

Boltzmann constant

Question 4

What are the assumptions of molecules in KINETIC THEORY? MAIN ONES

Answer 4

-R - random movement of particles
-A- attraction , none between particles
-V- volume, negligible volume of particles, compared to volume of gas
-E- elastic collisions between particles, no KE lost, Ek is conserved
-D- duration of collisions is very short, compared to time between collisions

Question 5

Behaviour of gases 3 things?

Answer 5

• Pressure ∝ 1/Volume at a constant temperature (T)
• Pressure ∝ Temperature at a constant volume
• Volume ∝ Temperature at a constant pressure

Question 6

How is pressure exerted by a gas on a container?

Answer 6

• molecules have random movement
• molecules collide with container wall and rebound (momentum changes)
  -Newton’s 2nd law- rate of change of momentum equal to force so the wall exerts a force on molecules
• Newton’s 3rd law- wall exerts force on molecule, molecule exerts force on wall of container, this force provides the pressure as p = F/A

Question 7

Units for mean square speed?

Answer 7

• m^2 s^-2

Question 8

Why do we use mean square speed?

Answer 8

-the energy of the PARTICLES is distributed randomly,
-way of representing the speed of an average molecule.

Question 9

Units for root mean square speed?

Answer 9

m s^-1.

Question 10

What is meant by Agrovado’s constant?

Answer 10

the number of particles in one mole of a substance.

Question 11

Molar mas equation?

Answer 11

M = Mr/1000

Question 12

What is Mr?

Answer 12

-relative molecular mass

Question 13

What 2 equations you need to show that the total
translational kinetic energy of a mole of a monatomic gas?

Answer 13

pV=nRT p= 1/3 N/V m c^2

Question 14

Expression for the total translational kinetic energy of a gas? derivation

Answer 14

-make second equation equal to pV
-equate them so we get nRT=1/3 Nmc^2
-multiply both sides by 3/2 so we get 3/2 nRT = 1/2 Nmc^2

• for ONE MOLE OF GAS , total translational kinetic energy 3/2 RT as for 1 mole n=1 and N=Na
  -so 3/2 RT = 1/2NaMc^2 (this is total translational kinetical energy
• so KE of 1 molecule is 3/2 RT

Question 15

What does 3/2 RT and 3/2 KT show about KE?

Answer 15

Since R and k are constants, these equations show that the kinetic energy is directly proportional to the absolute temperature of the gas.

Question 16

What can you get with number of moles?

Answer 16

n = N (number of molecules) /Na (Agravado’s number)

Question 17

How to get molecular mass?

Answer 17

Mass of one molecule/ average atomic mass (u)

Question 18

How to get mass from molar mass?

Answer 18

Molar mass x no of moles

Question 19

What does Q mean?

Answer 19

• heat flowing into system

Question 20

What does w mean?

Answer 20

-work done by system