Chapter 15 Ideal Gases Flashcards
What is the SI unit for amount of substance?
Mole (mol)
What is the mol?
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
How many atoms is 1 mole? what is this number?
6.02x10^23 atoms. This is avagadros constant
What is the kinetic theory of matter?
This is a model to describe the behaviour of atoms or molecules in an ideal gas
What is an ideal gas?
It is a simplification of the way that gasses act but is suitable for simple calculations
What are the 5 assumptions in the kinetic model made to form the ideal gas model?
- 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
How do ideal gasses cause pressure?
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
What is the force that is exerted on the wall? why?
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
What is the equation for pressure?
p = F / A
What is the relationship between pressure and volume?
pressure ∝ 1 / Volume
What is the relationship between pressure and temperature?
pressure ∝ Temperature
What is the ideal gas law?
pV/T = nR or pV = nRT p = Pressure V = Volume T = Temperature n = Number of moles R = Ideal gas constant
What is the equation to use if conditions are changing from one state to another?
p(init)V(init) / T(init) = p(fin)V(fin) / T(fin)
What is the relationship pV / T = nR called?
It is the equation of state of an ideal gas.
What is the molar gas constant? what is its units?
8.31 JK^-1mol^-1
What does the graph of pV against T show?
The gradient is nR. The steeper the line the greater the number of moles of gas
What is the average velocity of atoms / molecules in a gas?
0 ms^-1
How is the average speed calculated?
Using the root mean squared
What is the root mean squared in the context of finding the average speed of atoms in a gas?
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
What is the equation for pressure at a microscopic level?
pV = 1/3NmC̄^2 p = Pressure V = Volume N = Number of particles of gas C̄ = mean squared of the particles
What is a maxwell-boltzmann distribution?
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.
What happens to a maxwell-boltzmann distribution when the temperature is increased?
The most common speed and the r.m.s increase and the distribution becomes more spread out
What is boltzmanns constant? what is the equation? what is its value?
k = R / Na
8.31 / 6.02x10^23 = 1.38x10^-23 JK^-1
What are the two equations for ideal gasses that involve boltzmanns constant
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
How is the average kinetic energy calculated using Boltzmanns constant?
Ek = 3/2 kT Ek = Kinetic Energy k = Boltzmanns constant T = Temperature
All the particles around you have the same______. But their different ______ cause them to have different _______
Kinetic energy
Masses
Speeds
What is the internal energy of a gas?
It is the sum of all the kinetic and potential energies
What is the internal energy of an ideal gas?
It just the kinetic energy because we assume the electrostatic forces are negligable
What happens to the internal energy of an ideal gas if the temperature is doubled?
The kinetic energy doubles so the internal energy doubles
