Section 6 part 3 - gases Flashcards
What is the pressure of a gas?
Force per unit area that the gas exerts normally
What does the pressure of a gas depend on?
Temperature, volume of container, mass of gas in container
What is an isothermal change?
Any change at constant temperature
Define Boyle’s law
For a fixed mass of gas at constant temperature, the gas pressure multiplied by the volume of gas is a constant
What graph would you plot when investigating Boyle’s law to get a straight line graph?
Pressure against 1/Volume, as p/1/V = pV, representing y=mx, where y is pressure, gradient is constant, and x is 1/volume
What type of graph do you get for Boyle’s law when plotting pressure against volume?
Reciprocal looking curves, with higher temperatures shifting the curve to the right, or with p against 1/v, a steeper gradient for higher temps
Define Charles’ law
For an ideal gas at constant pressure, the volume divided by the temperature is a constant
What is an isobaric change?
Any change at constant pressure
What is the work done by a gas on a piston equal to when changing the volume of the gas?
Pressure x change in volume
Define the pressure law
For an ideal gas with a constant volume, the pressure divided by the temperature is a constant
What causes the pressure of a gas on a surface?
The gas molecules hitting the surface
What is Brownian motion?
The random motion particles travel, due to the individual molecules bombarding each particle unevenly and randomly
How did Robert Brown show the existence of molecules and atoms
With pollen grains in the water`
What happens to the Brownian motion when temperature is increased?
The motion gets more erratic, but stays random
How much greater is the density of oxygen than that of hydrogen at constant temperature?
x16
Define the Avogadro constant
The number of atoms in 12g of the carbon isotope of 12/6C . = 6.02e23
What is an atomic mass unit?
1/12th of the mass of a 12/6 Carbon atom.
What is molarity?
The number of moles in a given quantity of a substance. Unit mol
What is molar mass?
The mass of 1 mol of the substance, unit kg/mol
What does the number of moles in mass Ms of a substance equal?
Mass of the substance (Ms) / the molar mass
What does the number of molecules in mass Ms of a substance equal?
Avogadro’s constant (Na) x mass of the substance (Ms)/ molar mass
What is a mole?
One mole of a substance consisting of identical particles is defined as the quantity of substance that contains Na particles
What is an ideal gas?
A gas that obeys Boyle’s law
What is the equation for an ideal gas?
pV/T = constant for a fixed mass of ideal gas
What assumptions does the ideal gas equation make?
The pressure, volume and temperature of a fixed mass of gas all change
what is R in the equation pV=nRT?
Molar gas constant, 8.31 J/mol kelvin
What are the other equations for density of an ideal gas?
density = mass/volume = number of moles x molar mass of substance / volume. pressure x molar mass of substance/ R x temperature
What are the other equations for the density of an ideal gas (not worded)
density = nM/V, pM/RT
For an ideal gas at constant pressure, what is the relationship between density and the temperature?
The density is inversely proportional to the temperature
State what each component of the equation pV=nRT is
p = pressure V = volume n = number of moles R = molar gas constant, 8.31 T = Temperature
State what each component of the equation pV=NkT is
p = pressure V = volume N = number of molecules k = Boltzmann constant, R/Na, 1.38e-23 T = temperature
How do you convert from Celsius to Kelvin?
Celsius + 273
What happens to the root mean square when the temperature of the gas is raised?
The molecules move faster on average, so the rms increases
What happens to the distribution curve of the rms when the overall rms increases?
The curve becomes flatter and broader because there are more molecules moving at higher speeds
Briefly summarise the 5 assumptions made in the kinetic theory
- Molecules are point molecules
- Molecules do not attract each other
- Molecules move in continual random motion
- Collisions with the surface are elastic collisions
- Each collision with the container surface is of much shorter duration than the time between impacts
KE Theory assumption: Why do you assume the molecules are point molecules?
So the volume of each molecule is negligible when compared with the volume of the gas
KE Theory assumption: Why do you assume the particles do not attract each other?
If they did attract each other, the effect would be to reduce the force of their impacts on the container surface
KE Theory assumption: Why do you assume the collisions with each particle and the container surface are elastic
So there is no overall loss of kinetic energy in the collision
For an ideal gas, what is its internal energy given by?
The kinetic energy of the molecules in the gas
