15. Ideal Gas Flashcards
Module 15
Define 1 mole
the amount of substance that contains as many elementary entities as there are atoms in 0.012kg of carbon.
What is the Avogadro constant?
1 mol of any substance
(6.02 x 10^23)
What is the Kinetic theory of matter Model used for?
used to describe the behaviour of atoms or molecules in an ideal gas.
What are the five assumptions made about atoms (A) or molecules (M) in an ideal gas to keep the model simple
- gas contains very large num of A or M moving in random directions with random speeds
- A or M of gas occupy a negligible volume compared with the volume of the gas
- collision of A or M with eachother and the container walla are perfectly elastic (no Ke is lost)
- time of collisions between A or M is negligible compared to the time between collisions
- Electrostatic forces between A or M are negligible except during collisions
How can we use Assumptions and Newton’s Laws of motion to explain how A or M in an ideal gas cause pressure
A or M in a gas are always moving, so when they collide with the container wall, wall exerts a force, causing the momentum to change as the A or M bounce off the wall
When a single A collides with container wall elastically, the speed doesn’t change but the velocity goes from +u ms^-1 to -u ms^-1. The total change in momentum is -2mu.
According to Newton’s 2nd law: Force of atom = change in momentum/ change in time. Change in momentum = -2mu. Change in time is time between the collisions with the wall.
With Newton’s 3rd law: atom exerts an equal but opposite force on the wall.
Pressure = Force/ crossectional area
What happens to pressure if temp and mass of gas is constant?
pressure of ideal gas is inversely proportional to its volume V
What is Boyle’s Law? What experiment is related to it?
Boyle’s Law is pressure is proportional to 1/V. (V = volume)
Experiement:
If pressure is reduced of a pressurised gas, its volume increases. The gas must be in a sealed tube to exnsure the gas inside tube remains constant.
What happens to pressure of ideal gas when volume and mass of gas is constant?
If volume and mass of gass is constant,
pressure of ideal gas is directly proportional to absolute temp (T) in kelvin.
What experiment can be used to calculate absolute zero estimation?
Figure 5 in kerboodle page 290
temp of water bath increases and results to a rise in pressure of gas in sealed vessel.
At absolute zero, particles would not be moving (internal energy is at zero) so pressure must be zero.
Plot a graph of pressure against temp in degree C. We can use graph to look at the point where pressure is zero
By combining the proportionalities of pressure with temp and volume, what can we work out?
By combining,
p = 1/V and p = T
we know pV/T = constant
so to change from one state to final
P(intial)V(initial) / T(initial) = P(final)V(final) / T(final)
Give the first equation of state of ideal gas. How would you plot this on a graph?
Molar gas constant, R = 8.31 JK^-1mol^-1
n = num of moles of gas
pV/T = nR or pV = nRT
Plotting this on a graph:
nR would be the gradient
the greater the num of moles of gas, the steeper the line
Define root mean square speed
a measure to use for the typical motion of particles inside the gas
How would you work out the r.m.s speed?
Velocity of each A or M in gas is squared. Then average of squared velocity is seen as the mean square speed of gas particles ( c^2 with bar above). Finally, you square root the value to give r.m.s speed.
What is the formula of pressure at a microscopic level?
pV = 1/3 Nmc^2 (with bar above)
p = pressure
V = volume
N = num of particles in gas
m = mass of each particle
c^2 bar above = mean square speed
Define Boltzmann constant. What is the value of it, state the unit? What is the formula?
Boltzmann constant, k, is used to relate the mean kinetic energy of A or M in gas to gas temp
k = molar gas constant / avogadro constant
k = R/N(down)A
k = 1.38 x 10^23 JK^-1
