Section 6 part 3 - gases

Question 1

What is the pressure of a gas?

Answer 1

Force per unit area that the gas exerts normally

Question 2

What does the pressure of a gas depend on?

Answer 2

Temperature, volume of container, mass of gas in container

Question 3

What is an isothermal change?

Answer 3

Any change at constant temperature

Question 4

Define Boyle’s law

Answer 4

For a fixed mass of gas at constant temperature, the gas pressure multiplied by the volume of gas is a constant

Question 5

What graph would you plot when investigating Boyle’s law to get a straight line graph?

Answer 5

Pressure against 1/Volume, as p/1/V = pV, representing y=mx, where y is pressure, gradient is constant, and x is 1/volume

Question 6

What type of graph do you get for Boyle’s law when plotting pressure against volume?

Answer 6

Reciprocal looking curves, with higher temperatures shifting the curve to the right, or with p against 1/v, a steeper gradient for higher temps

Question 7

Define Charles’ law

Answer 7

For an ideal gas at constant pressure, the volume divided by the temperature is a constant

Question 8

What is an isobaric change?

Answer 8

Any change at constant pressure

Question 9

What is the work done by a gas on a piston equal to when changing the volume of the gas?

Answer 9

Pressure x change in volume

Question 10

Define the pressure law

Answer 10

For an ideal gas with a constant volume, the pressure divided by the temperature is a constant

Question 11

What causes the pressure of a gas on a surface?

Answer 11

The gas molecules hitting the surface

Question 12

What is Brownian motion?

Answer 12

The random motion particles travel, due to the individual molecules bombarding each particle unevenly and randomly

Question 13

How did Robert Brown show the existence of molecules and atoms

Answer 13

With pollen grains in the water`

Question 14

What happens to the Brownian motion when temperature is increased?

Answer 14

The motion gets more erratic, but stays random

Question 15

How much greater is the density of oxygen than that of hydrogen at constant temperature?

Answer 15

x16

Question 16

Define the Avogadro constant

Answer 16

The number of atoms in 12g of the carbon isotope of 12/6C . = 6.02e23

Question 17

What is an atomic mass unit?

Answer 17

1/12th of the mass of a 12/6 Carbon atom.

Question 18

What is molarity?

Answer 18

The number of moles in a given quantity of a substance. Unit mol

Question 19

What is molar mass?

Answer 19

The mass of 1 mol of the substance, unit kg/mol

Question 20

What does the number of moles in mass Ms of a substance equal?

Answer 20

Mass of the substance (Ms) / the molar mass

Question 21

What does the number of molecules in mass Ms of a substance equal?

Answer 21

Avogadro’s constant (Na) x mass of the substance (Ms)/ molar mass

Question 22

What is a mole?

Answer 22

One mole of a substance consisting of identical particles is defined as the quantity of substance that contains Na particles

Question 23

What is an ideal gas?

Answer 23

A gas that obeys Boyle’s law

Question 24

What is the equation for an ideal gas?

Answer 24

pV/T = constant for a fixed mass of ideal gas

Question 25

What assumptions does the ideal gas equation make?

Answer 25

The pressure, volume and temperature of a fixed mass of gas all change

Question 26

what is R in the equation pV=nRT?

Answer 26

Molar gas constant, 8.31 J/mol kelvin

Question 27

What are the other equations for density of an ideal gas?

Answer 27

density = mass/volume = number of moles x molar mass of substance / volume. pressure x molar mass of substance/ R x temperature

Question 28

What are the other equations for the density of an ideal gas (not worded)

Answer 28

density = nM/V, pM/RT

Question 29

For an ideal gas at constant pressure, what is the relationship between density and the temperature?

Answer 29

The density is inversely proportional to the temperature

Question 30

State what each component of the equation pV=nRT is

Answer 30

p = pressure
V = volume
n = number of moles
R = molar gas constant, 8.31
T = Temperature

Question 31

State what each component of the equation pV=NkT is

Answer 31

p = pressure
V = volume
N = number of molecules
k = Boltzmann constant, R/Na, 1.38e-23
T = temperature

Question 32

How do you convert from Celsius to Kelvin?

Answer 32

Celsius + 273

Question 33

What happens to the root mean square when the temperature of the gas is raised?

Answer 33

The molecules move faster on average, so the rms increases

Question 34

What happens to the distribution curve of the rms when the overall rms increases?

Answer 34

The curve becomes flatter and broader because there are more molecules moving at higher speeds

Question 35

Briefly summarise the 5 assumptions made in the kinetic theory

Answer 35

1. Molecules are point molecules
2. Molecules do not attract each other
3. Molecules move in continual random motion
4. Collisions with the surface are elastic collisions
5. Each collision with the container surface is of much shorter duration than the time between impacts

Question 36

KE Theory assumption: Why do you assume the molecules are point molecules?

Answer 36

So the volume of each molecule is negligible when compared with the volume of the gas

Question 37

KE Theory assumption: Why do you assume the particles do not attract each other?

Answer 37

If they did attract each other, the effect would be to reduce the force of their impacts on the container surface

Question 38

KE Theory assumption: Why do you assume the collisions with each particle and the container surface are elastic

Answer 38

So there is no overall loss of kinetic energy in the collision

Question 39

For an ideal gas, what is its internal energy given by?

Answer 39

The kinetic energy of the molecules in the gas