Kinetic TheoryEnergy Transformations Between States of Matter

Kinetic Theory:

• An explanation for how particles move and behave1. All matter is comprised of small particles (atoms, molecules, ions)2. These particles are in constant, random motion3. These particles therefore collide with one another.

• These particles lose some energy during collisions with other particles, but the amount lost is very small and can be neglected in most cases.

Thermal Energy

• Atoms in solids are held tightly in place by the attraction between the particles. This attraction gives the particles definite shape and volume.• Thermal energy (the total energy of a material’s particles)

causes the particles to vibrate in place. (usually making them warm, thus the term, thermal)• More thermal energy = faster movement• Less thermal energy = slower movement

Average Kinetic Energy

• Temperature is not just a measure of hot or cold something is. • Since heat implies thermal energy, temperature is actually

a measure of the average kinetic energy of the particles in a substance. (how fast they are moving)• Higher temperature = faster movement• Lower temperature = slower movement• At absolute zero (-273.15 C or 0 Kelvin) particle motion is

so slow that no additional thermal energy can be removed from a substance.

Solid State

• Particles packed closely together and have an ordered arrangement

• Most solid materials have a specific geometric arrangement in which they form when cooled. THIS IS IMPORTANT.

• Chemical and physical properties of solids often can be attributed to the type of geometric arrangement that the solid forms.

Liquid State

• For a solid to change to a liquid, thermal energy must be added• Particles begin to vibrate faster and collide with each other

(transferring energy)• Eventually, the particles will have enough KE to overcome the

attractive forces and slip out of their ordered arrangement (melting point)• Melting point is the temperature at which solids begin to liquefy.

This differs from material to material• Heat of fusion is the energy required to change a substance from

the solid phase to the liquid phase at its melting point.

Liquid State Continued

• Liquids flow, in other words, particles have more KE than particles in a solid

• Extra energy allows them to partially overcome the attractions of other particles and the particles slide past each other.

• Liquids have no definite shape, but definite volume.

Gas Stage

• More KE than liquid particles and have enough KE to overcome the attractions between them.

• No definite shape or volume.• For a liquid to change to a gas, more thermal energy must be added• Particles move fast enough to escape the attractive forces of other

particles and enter the gas state (Vaporization)• Evaporation is vaporization that occurs at the surface of a liquid.

1. Can occur below a liquid’s boiling point2. Particles must be at the liquids surface, traveling away from

the liquid and have enough KE to escape the attractive forces.

Gas Stage Continued

• Boiling point: another way liquid can vaporize and occurs throughout a liquid at a specific temperature depending on the pressure on the surface of the liquid.

• Boiling point is the temperature at which the pressure of the vapor in the liquid is equal to the external pressure acting on the surface of a liquid.

• External pressure is a force pushing down on a liquid keeping particles from escaping and particles require energy to overcome that force.

• Heat of vaporization is the amount of energy required for the liquid at its boiling point to become a gas.

Gas Stage Continued

• Gases fill their containers.• Gas particles move so quickly that they have overcome the

attractive forces between them.• The movement of particles and the collisions between them

cause gases to diffuse.• Diffusion is the spreading of particles throughout a given

volume until they are uniformly distributed.

Summary to this point:

• 3 states of matter: solid, liquid, gas

• Energy is required to transition in the order listed above. To go backwards, energy must be removed.

• Generally speaking, as solids move to liquids and then to gases, the particles expand. Going backward, they contract.

Heating Curve of a Liquid

• A heating curve is a graph that shows the temperature change of a substance as thermal energy, or heat, is added.• There are two areas on the graph that will always be

present1. Melting point: solid -> liquid2. Boiling point: liquid -> gas

Plasma state• The 4th state of matter

• Plasma consists of positively and negatively charged particles

• Overall charge is neutral because there is an equal number of positive and negative charges.

• Particles will move faster as the matter is heated to higher temperatures

• The faster the particles move, the greater the force when they collide

• The forces produced from high energy ollisions are so great that electrons are stripped from the atoms, thus the + and – charges.

• Examples: stars, lightning bolts, neon and fluorescent tubes, auroras

Thermal Expansion

• Expansion in solid matter: Particles move faster and separate as the temperature rises. This separation of particles results in an expansion of the entire object.• Thermal expansion is an increase in the size of a substance

when the temperature is increased.• When the temperature of an object is lowered, particles

slow down. The attraction between them increases and the particles move closer together. The lessened movements of particles that are closer together results in an overall shrinking of the object known as contraction.

Thermal Expansion

• Expansion of liquids: thermometer, addition of energy causes particles in liquid to move faster and father apart.• Expansion of gases: hot air balloon, air in balloon is

heated, causing distance between particles to increase, and as the balloon expands, the number of particles per cubic centimeter decreases.• This results in a decreased density of the hot air and since

the density of hot air in the balloon is then lower than the density of cooler air outside, the balloon will rise.

Strange behavior of water

• Most substances expand as temperature rises, but not water• Water molecules have highly positive and highly negative areas• These charged regions affect the behavior of water• As temperature drops, particles move closer together. Unlike charges

attracted to each other and line up so that the only positive and negative zones are near to each other (think of magnets)

• Because water molecules orient themselves according to charge, empty spacces occur in the structure.

• Empty spaces are larger in ice than in a liquid, so water expands when going from liquid to solid which is OPPOSITE of most other materials.

• Solid ice is less dense than water, so it floats.

Solid or Liquid?

• There are substances that exhibit unusual behaviors when changing states.

• Amorphous solids: Do not have a definite temperature at which they change from solid to liquid. They soften and gradually turn into a liquid over a temperature range and lack the highly ordered crystalline structure found in regular solids. Examples are glass and plastic.

Amorphous Solids continued

• Particles are typically long, chainlike structures that can get jumbled and twisted instead of being neatly stacked in geometric arrangements.• Interactions between the particles occur along the chain,

which gives amorphous solids different properties than crystals.• Some of these amorphous solids form when liquid matter

changes to solid matter too quickly for an orderly structure to form. Obsidian forms when lava cools too quickly.

Liquid Crystals

• Normally, the ordered geometric structure of a solid’s particles is lost when the substance turns into a liquid.• Liquid crystals start to flow during the melting phase

similar to a liquid, but they do not lose their ordered arrangement completely.• They are placed in classes depending upon the type of

order they maintain when they liquefy. • They are highly responsive to temperature changes and

electric fields.• LCD displays.

QUIZ TIME

• Put away your notes, if you’re taking them.• You DO NOT need a calculator.

Properties of Fluids

• How do ships float?

1. Archimedes’ Priciplea. Greek mathematician that found that the buoyant

force on an object was equal to the weight of the fluid displaced by the object.

2. Density: An object will float if its density is less than the density of the fluid it is placed in.

Pascal’s Principle

• Pressure is force exerted per unit area, or P = F/A• Blaise Pascal discovered that applying pressure to a fluid transmitted

that pressure throughout the fluid.• But what does this mean?

1. Hydraulic machines can move heavy loads in accordance with Pascal’s principle.2. A pipe filled with fluid connects small and large cylinders.

Pressure applied to the small cylinder is transferred through the fluid to the large one and since pressure remains constant in the fluid more force is available to lift a heavy load by increasing the surface area

Bernoulli’s Principle

• As the velocity of a fluid increases, the pressure exerted by the fluid decreases.

Fluid Flow

• Viscosity is the resistance to flow by a fluid.• This varies from fluid to fluid. A low viscosity means fast

movement, but a high viscosity means _____ movement.

• Flowing particles transfer energy to stationary particles. If the particles begin to pull the stationary particles into motion easily, then the liquid has a low viscosity, or low resistance to flow. The opposite is also true.

Gas Behavior and Laws

• Pressure is the amount of force exerted per unit area. What do you know of that maintains pressure? Why does it maintain its shape?

• Pressure is measured in pascals (Pa) but since a pascal is so small, we use kilopascals (kPa) which means 1000 pascals.• At sea level, the atmospheric pressure is 101.3 kPa.

Boyle’s Law

• If temperature remains constant and you decrease the volume of a container, the pressure of the gas will increase. • So, if you increase the volume of a container, pressure will

decrease.

• P1*V1 = P2*V2 P is pressure, V is volume

The Pressure-Temperature Relationship

• At a constant volume, an increase in temperature results in an increase in pressure

Charles’ Law

• As long as pressure remains constant, when volume of a gas increases as temperature increases. The volume will decrease with decreasing temperature.• Kinetic Theory of Matter (remember?) states that the

particles move faster as something is heated so if they move faster they strike the walls of their container with more force which makes the walls expand.• V1/T1 = V2/T2 T is temp in K, V is volume