Kinetic Molecular Theory -- Need 2 Know Flashcards
What is the ideal gas law?
PV = nRT
P –> Pressure (atm)
V –> Volume (L)
n –> moles
R –> universal constant (0.0821)
T –> temperature (K)
If the moles within a system increase (at a constant T and V), what happens to the collision force and why?
There is no change with the collision force. They continue to hit the wall of the container with the same amount of force, since there is nothing that has been done to affect that.
If the moles within a system increase (at a constant T and V), what happens to the collision frequency and why?
The frequency of collisions increases. Since there are more moles to hit the walls of the container, the frequency goes up the more that is added to collide with.
If the volume of a system increases (at a constant T and n), what happens to the collision force and why?
There is no change in the collision force. An increase in volume does not cause the moles within the container to hit the wall with less force, as it doesn’t affect its process.
If the volume of a system increases (at a constant T and n), what happens to the collision frequency and why?
The frequency of collisions decreases as the volume grows. When volume grows, pressure decreases (in accordance with Boyle’s Law). When pressure decreases, the frequency of moles hitting the wall decreases.
If the temperature of a system increases (at a constant n and V), what happens to the collision force and why?
The collision force increases as the temperature rises. This is due to the more rapid random movements of the particles. The speed of particles increases when temperature is raised, therefore, the force is stronger.
If the temperature of a system increases (at a constant V and n), what happens to the collision frequency and why?
The collision frequency of the moles increases, because the temperature rise causes more rapid movements, therefore causing more collisions at a higher frequency.
Boyle’s Law
States that pressure (P) is equal to one over the volume (V) of the container the system is held in.
(P = 1 / V)
If we compress a gas without a change in its temperature, the average KE of the gas particles stays the same. There is no change in the speed with which the particles move, but the container is smaller. Thus, the particles travel from one end of the container to the other in a shorter period of time. This means that they hit the walls more often. Any increase in the frequency of collisions with the walls must lead to an increase in the pressure of the gas. Thus, the pressure of a gas becomes larger as the volume of the gas becomes smaller.
Charles’ Law
States that the volume (V) of the container holding the system is proportional to the temperature (T) of the system.
(V is proportional to T)
→ “Proportional to” symbol is an infinity sign with the right half opened
The average kinetic energy of the particles in a gas is proportional to the temperature of the gas. Because the mass of these particles is constant, the particles must move faster as the gas becomes warmer. If they move faster, the particles will exert a greater force on the container each time they hit the walls, which leads to an increase in the pressure of the gas. If the walls of the container are flexible, it will expand until the pressure of the gas once more balances the pressure of the atmosphere. The volume of the gas therefore becomes larger as the temperature of the gas increases.
Amontons’ Law
States that the pressure (P) of the system is directly proportional to the change of the temperature (T) of the system.
(P is directly proportional to T)
The average kinetic energy of a gas particle depends only on the temperature of the gas. Thus, the average KE of the gas particles increases as the gas becomes warmer. Because the mass of these particles is constant, their kinetic energy can only increase if the average velocity of the particles increases. The faster these particles are moving when they hit the wall, the greater the force they exert on the wall. Since the force per collision becomes larger as the temperature increases, the pressure of the gas must increase as well.
The link between P and n
The pressure of a gas results from collisions between the gas particles and the walls of the container. Each time a gas particle hits the wall, it exerts a force on the wall. An increase in the number of gas particles in the container increases the frequency of collisions with the walls and therefore the pressure of the gas.
Avogadro’s Hypothesis
The volume (V) of the container holding the system is directly proportional to the amount of moles (n) the system has.
(V is directly proportional ton)
As the number of gas particles increases, the frequency of collisions with the walls of the container must increase. This, in turn, leads to an increase in the pressure of the gas. Flexible containers, such as a balloon, will expand until the pressure of the gas inside the balloon once again balances the pressure of the gas outside. Thus, the volume of the gas is proportional to the number of gas particles.
