3.3 The Kinetic Model Of Gases Flashcards
What is pressure?
The normal force per unit area acting on the surface.
What is the formula for pressure?
P = (Fcos@)/A
What are the units of pressure?
Nm^-2
What is important about a gas colliding?
A gas is very large collection of molecules with intermolecular distances larger than in solid and liquids.
If gas collides at right angles with wall of container and rebounding, molecules experiences force because momentum has changed from mv to -mv, magnitude of momentum changed by amount of 2mv. Force by molecule on wall. Pressure is result of force of many molecules colliding with walls.
What are the two factors that affect the pressure of a gas?
Average speed of molecules.
Frequency with which molecules collide with walls.
What are the assumptions of the ideal gases?
Molecules are hard spheres of negligible volume.
Collisions between molecules and between molecules and walls are elastic.
Duration of collisions is short compared to time between collisions.
No forces between molecules except during contact.
Molecules move randomly with range of speeds.
Molecules obey law of mechanics.
What is important about real gases?
Unlike ideal gases can be liquified or solidified.
Always has intermolecular forces.
Internal energy include intermolecular potential energy.
ideal gas is good approximation to real gases at low density. Likely to find gas at low density under conditions of large volume, low pressure and moderate temperature.
What is important about evaporation?
Liquid can evaporate at any temperature. Evaporation process involves surface molecules only, rate of evaporation increase with increasing temperature and surface area of liquid.
What is important about boiling?
A liquid boils at specific temperature, molecules from anywhere in the liquid can leave.
Why is evaporation accompanied by cooling?
Faster molecules will escape leaving behind slower ones - average speed and average kinetic energy of molecules left behind decrease. Temperature is measure of average kinetic energy of molecules, therefore temperature decreases.
How is the state of gas determined?
pV=nRT
How can you use this formula to find new values of pressure, volume, number of moles and temperature, after a change in the state of a gas?
p1V1/n1T1 = p2V2/n2T2
