Chapter 15 Ideal Gases

Question 1

What is the SI unit for amount of substance?

Answer 1

Mole (mol)

Question 2

What is the mol?

Answer 2

It is a number of atoms which when you have that number of atoms the mass is equal to the molar mass of that substance in grams.
e.g. 1 Mole of carbon-12 weights 12 grams

Question 3

How many atoms is 1 mole? what is this number?

Answer 3

6.02x10^23 atoms. This is avagadros constant

Question 4

What is the kinetic theory of matter?

Answer 4

This is a model to describe the behaviour of atoms or molecules in an ideal gas

Question 5

What is an ideal gas?

Answer 5

It is a simplification of the way that gasses act but is suitable for simple calculations

Question 6

What are the 5 assumptions in the kinetic model made to form the ideal gas model?

Answer 6

• The gas contains a very large number of atoms moving in random directions with random speeds
• The atoms or molecules of gas occupy a negligible volume compared with the volume of the gas
• The collusions of atoms or molecules with each other and the container wall are perfectly elastic
• The time of collisions between the atoms or molecules is small compared with the time between collision
• Electrostatic forces between atoms or molecules are negligible except during collisions

Question 7

How do ideal gasses cause pressure?

Answer 7

The atoms / molecules in the gas are always moving and the collision between them an the wall of the container exerts a force on the container. This is pressure

Question 8

What is the force that is exerted on the wall? why?

Answer 8

It is 2mu/Δt. This is because there is the force that is exerted by the atom on the wall and the force that the wall exerts on the atom. This is because it is an elastic collision

Question 9

What is the equation for pressure?

Answer 9

p = F / A

Question 10

What is the relationship between pressure and volume?

Answer 10

pressure ∝ 1 / Volume

Question 11

What is the relationship between pressure and temperature?

Answer 11

pressure ∝ Temperature

Question 12

What is the ideal gas law?

Answer 12

pV/T = nR or pV = nRT
p = Pressure
V = Volume
T = Temperature
n = Number of moles
R = Ideal gas constant

Question 13

What is the equation to use if conditions are changing from one state to another?

Answer 13

p(init)V(init) / T(init) = p(fin)V(fin) / T(fin)

Question 14

What is the relationship pV / T = nR called?

Answer 14

It is the equation of state of an ideal gas.

Question 15

What is the molar gas constant? what is its units?

Answer 15

8.31 JK^-1mol^-1

Question 16

What does the graph of pV against T show?

Answer 16

The gradient is nR. The steeper the line the greater the number of moles of gas

Question 17

What is the average velocity of atoms / molecules in a gas?

Answer 17

0 ms^-1

Question 18

How is the average speed calculated?

Answer 18

Using the root mean squared

Question 19

What is the root mean squared in the context of finding the average speed of atoms in a gas?

Answer 19

This is when the velocity is squared (so the negative numbers are removed), then this is averaged and then square rooted.
√C̄^2 = Cr.m.s

Question 20

What is the equation for pressure at a microscopic level?

Answer 20

pV = 1/3NmC̄^2
p = Pressure
V = Volume
N = Number of particles of gas
C̄ = mean squared of the particles

Question 21

What is a maxwell-boltzmann distribution?

Answer 21

It is a graph of speed on the x-axis and the number of particles with that speed on the y-axis.
The highest part is the most probable speed of a particle.
The graph always goes through 0,0.

Question 22

What happens to a maxwell-boltzmann distribution when the temperature is increased?

Answer 22

The most common speed and the r.m.s increase and the distribution becomes more spread out

Question 23

What is boltzmanns constant? what is the equation? what is its value?

Answer 23

k = R / Na

8.31 / 6.02x10^23 = 1.38x10^-23 JK^-1

Question 24

What are the two equations for ideal gasses that involve boltzmanns constant

Answer 24

pV = NkT
1/2mC̄^2 = 3/2kT

p = Pressure
V = Volume
N = Number of particles
k = Boltzmanns constant = 1.38x10^-23
T = Temperature
m = Mass of each particle
C̄ = Mean speed

Question 25

How is the average kinetic energy calculated using Boltzmanns constant?

Answer 25

Ek = 3/2 kT
Ek = Kinetic Energy
k = Boltzmanns constant
T = Temperature

Question 26

All the particles around you have the same______. But their different ______ cause them to have different _______

Answer 26

Kinetic energy
Masses
Speeds

Question 27

What is the internal energy of a gas?

Answer 27

It is the sum of all the kinetic and potential energies

Question 28

What is the internal energy of an ideal gas?

Answer 28

It just the kinetic energy because we assume the electrostatic forces are negligable

Question 29

What happens to the internal energy of an ideal gas if the temperature is doubled?

Answer 29

The kinetic energy doubles so the internal energy doubles