The Kinetic Molecular Theory Of Gases Properties of Gases The Kinetic Molecular Theory Of Gases

What do you already know? Shape Volume Movement Particles Temperature Pressure

Real gas vs Ideal gas There are many assumptions we make about how gases behave in order to apply simple math to them Throughout the lecture, try to form an answer to this question: Why do gases act most like ideal gases at high temperatures and low pressures?

Ideal Gas An ideal gas is a gas that follows all the assumptions of the Kinetic Molecular Theory

Kinetic Molecular Theory: Overview Describes how gas molecules behave under different conditions Explains the physical properties that gases exhibit Consists of 5 specific assumptions

1st Assumption: “Gases consist of large numbers of tiny particles that are far apart relative to their size” What this means: Molecules in gases are about 1000 times further apart from each other than liquid or solid molecules Gases have extremely low densities

2nd Assumption: “Collisions between gas particles and between particles and container walls are elastic collisions.” What this means: Elastic collision - a collision in which there is no net loss of kinetic energy Particles bounce apart without loosing any of their original energy or momentum

2nd Assumption: Elastic Collisions The initial velocity of the gas particles is the same velocity they have after a collision Because no energy is changed when gas particles collide with another object, they do not interact permanently

3rd Assumption: Particles continually move bounce and change direction “Gas particles are in continuous rapid, random motion. They therefore posses kinetic energy, which is the energy of motion.” What this means: Gas particles are always moving described as constant random motion Gas particles move in all directions within their container Particles continually move bounce and change direction within their container because they posses kinetic energy

4th Assumption: Particles continually move bounce and change direction “There are no forces of attraction or repulsions between gas particles.” What this means: Gas particles are always moving described as constant random motion Gas particles move in all directions within their container Particles continually move bounce and change direction within their container because they posses kinetic energy

5th Assumption: “The average kinetic energy of gas particles depends on the temperature of the gas.” What this means: Temperature causes gas molecules to move more quickly KE = 1/2 mv2 Higher velocity produces a higher kinetic energy At the same temperature, lighter molecules move more quickly than heavier gas molecules

Properties that result from the KMT Expansion Diffusion Effusion Fluidity Compressibility

Fluidity Fluidity- molecules of gases flow across each other and throughout their container Which assumption leads to this theory? 2nd assumption – elastic collisions between particles ensure they do not stick together 3rd assumption - gas particles are always moving

Compressibility Compressibility – gas particles can be forced into a smaller space Which assumption leads to this property? 1st assumption – particles are far apart so there is room to for them to fill

Expansion Gas will expand to fill their container Which assumption leads to this property? 3rd assumption – gases are in constant random motion The particles do not settle in any one space to create a definite volume The particles in the solid and liquid settle at the bottom of the container, but the particles in the gas never stop moving and thus never settle

Diffusion Diffusion – spontaneous mixing of the particles of two substances caused by their random motion Gas particles will mix to fill their container Which assumption leads to this principle? 3rd assumption – same as expansion

Effusion Effusion – a process by which gas particles pass through a tiny opening Which assumption leads to this property? 3rd assumption – because the gas particles are always moving they will eventually move to the location of the opening and go through it We will go through effusion in much greater detail later