Physics - Recall for Chapter 15; Ideal Gases
Recall Questions
What is an ideal gas?
A theoretical gas that obeys the gas laws at all pressures and temperatures.
What is the kinetic theory assumption concerning volume?
The volume of the particles in a gas is negligible compared to the volume of the container.
What is the kinetic theory assumption concerning forces?
There are no electrostatic forces between particles except during collisions.
What is the kinetic theory assumption concerning motion?
Large number of atoms or molecules that are in moving continuously in random directions with random speeds.
What is the kinetic theory assumption concerning collisions?
The particles collide elastically with the walls of each other and the walls of the container.
What is the kinetic theory assumption concerning time?
The duration of collisions is negligible compared to the time between collisions.
What is the physical basis of Avagadro’s constant?
A number of particles equal to the number of atoms in 12 grams of carbon-12.
What is one mole of a substance?
An amount in which the number of atoms/molecules is equal to Avogadro’s constant.
What is the molar mass of a substance?
The mass of one mole of a substance.
How do you find the mass of one atom from its nucleon number?
Multiply nucleon number by the atomic mass unit (u) in kg.
How is the atomic mass unit defined?
It is $1/12$th the mass of a Carbon-12 atom.
How do you calculate the number of particles from the number of moles of a substance?
How do you find the molar mass of a substance from the molecular mass?
How do you find the molar mass of an element from its nucleon number?
Molar mass is equal to nucleon number in grams.
How do you find the total mass of a substance from the number of moles?
How do you calculate the number of moles of a substance from the number of particles?
According to Newton’s second law if a particle experiences a change in momentum, then…?
There must be a force acting on the particle.
According to Newton’s third law if a container exerts a force on a particle, then…?
The particle must exert a force on the container.
What are the SI units of pressure?
What is the definition of pressure?
The force per unit area exerted normally to a surface.
What is Boyle’s law: Pressure is inversely proportional to…?
Volume for a fixed mass of gas at constant temperature.
What is Charles’ law: Volume is proportional to…?
Absolute temperature for a fixed mass of gas at constant pressure.
What is Gay Lussac’s Law: Pressure is proportional to…?
Absolute temperature for a fixed mass of gas at constant volume.
What is Avogadro’s law: Volume occupied by a gas is proportional to…?
Number of particles/moles if pressure and temperature are constant.
What is the equation of state for an ideal gas?
or
\[pV = nRT\]What is $R$ in $pV = nRT$?
Molar Gas Constant.
What is $N$ in $pV = NkT$?
Number of particles.
What is $n$ in $pV = nRT$?
Number of moles.
What is $k$ in $pV = NkT$?
Boltzmann constant.
What is the Boltzmann constant?
The molar gas constant, $R$, divided by Avogadro’s constant, $N _ A$.
What units of temperature should be used in the ideal gas equation?
Kelvin.
How do you find absolute zero from a pressure temperature graph?
Extrapolate the line to find the x-intercept.
Why does increasing the temperature of an ideal gas increase pressure?
Particles have greater kinetic energy so there is a greater rate of collisions and greater change in momentum per collision.
Why does increasing the volume of an ideal gas decrease pressure?
$P=F/A$. Force exerted decreases as the rate of collisions with the container decreases and the surface area increases.
How do you calculate root mean square speed of a gas?
Square the magnitude of the velocity of each individual gas molecule, take the average of these values and then take the square root.
Why is root mean square speed used instead of velocity?
Average velocity is zero.
What is the relationship between root mean square speed of particles in a gas and absolute temperature?
What is $N$ in $pV = \frac{1}{3}N m c^2$?
Number of particles.
What is $c^2$ in $pV = \frac{1}{3} N m c²$?
Mean square speed.
What is $\frac{3}{2}kT$ equal to?
The mean kinetic energy of a gas particle.
What form is the internal energy of an ideal gas?
Purely kinetic (i.e. no potential energy).
Why is there no potential energy in an ideal gas?
Because there are no force between particles (except during collisions).
What is $\frac{3}{2}NkT$ equal to?
Total internal energy of an ideal gas.
What is the relationship between absolute temperature and the average KE of particles in a substance?
Absolute temperature is proportional to average kinetic energy of the particles in a substance.