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IT’S A GAS…. The Nature of Gases. Gases have some interesting characteristics that have fascinated scientists for 300 years. The first gas to be studied was air & it was a long time before it was discovered that air was actually a mixture of particles rather than a single gas .
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The Nature of Gases • Gases have some interesting characteristics that have fascinated scientists for 300 years. • The first gas to be studied was air& it was a long time before it was discovered that air was actually a mixture of particles rather than a single gas. • Although air is a mixture of several different gases, it behaves much the same as any single gas.
Kinetic Molecular Theory • The Kinetic Molecular Theory of Matter. Is used to explain the behaviors and characteristics of ideal gases • The theory states that the tiny particles in all forms of matter are in constant motion. • There are 5 basic assumptions of the KMT as it applies to ideal gases. • Ideal gases are “perfect” gases that are used as a model to describe characteristics of real gases.
KMT Assumption #1 • A gas is composed ofsmall hardparticles. • The particles have an • insignificant volume and • are relatively far apart from one another. • There isempty spacebetween particles.
elastic collisions inelastic collisions KMT Assumption #2 • All collisions a gas particle undergoes areperfectly elastic. • They exert a pressure but don’t lose any energy during the collisions.
KMT Assumption #3 & #4 • The particles in a gas move inconstant random motion. • Particles move in straight paths and are completely independent of each of other • Particles path is only changed bycollidingwith another particle or the sides of its container. • No attractive or repulsive • forces between particles.
KMT Assumption #5 • All gas particles at the same temperature have the same kinetic energy • K.E. = ½ (mass) (velocity)2 • The speed of a molecule is • Directly related to its Kelvin • Temperature
The Nature of Gases • Regardless of their chemical identity, gases tend to exhibit similar physical behaviors • Gas particles can be monatomic (Ne), diatomic (N2), or polyatomic (CH4) – but they all have some common properties:
The Nature of Gases Common Properties of all gasses. • Gases have a small mass but can take a large volume. (Low Density) • Gases can be squeezed together.(Compressibility) • Gases fill their containers. (Expansion) • Gases diffuse. (Diffsion & Effusion) • Gases flow easily and without resistance throughout their container. (Fluidity)
Gases “R” squeezable • If you squeeze any gas, its volume can be reduced considerably • Gases have a low density which allows for a lot of empty space between gas molecules.
Gases fill their containers • Gases expand until they take up as much room as they possibly can. • Gases spread out to fill containers until the concentration of gases is uniformthroughout the entire space. • This is why that no- where around you is there an absence of air.
Gases diffuse • Gases can move through each other rapidly. • The movement of one substance through another is called diffusion. • Because of all of the empty space between gas molecules, another gas molecule can pass between them until each gas is spread out over the entire container, the gases mix uniformly.
Gases flow past other gases! • If I opened up a bag of popcorn in front of the class you would soon be able to smell it in the back. • The popcorn smell easily diffuses throughout the other gas molecules in the room.
Diffusion or Effusion • When gas molecules randomly move about a room it is called diffusion. • When gas molecules pass through a tiny opening it is called effusion. • Some gases diffuse more rapidly • then other gases based on • their size and their energy. • The heavier and colder the gas • the slower it moves.
REAL Gases are almost IDEAL. • Real Gases act like IDEAL gasses at high Temperatures and Low Pressures. • We live at relatively high • temperatures and Low pressures. • Real Gases differ from Ideal gases in that real gas molecules have mass and they have intermolecular forces effecting the molecules themselves.
A Real Gas can change its State This is how your shocks an struts work in your car. • That empty space can be compressed by pressure allowing gas particles less room to move around thus decreasing the volume while increasing the Density. • But be careful to much pressure can change a gas into a _________! LIQUID
Gas variables • Experimental work in chemistry requires the measurement of such quantities as volume, temperature, pressure, and the amount of sample. • In order to describe a gas sample completely and then make predictions about its behavior under changed conditions, it is important to deal with the values of: 1) amount of the gas (# of moles) 2) volume 3) temperature 4) pressure
