Conceptual Chemistry
Objective 1
Describe, at the molecular level, the difference between a gas, liquid, and solid phase.
Solids
Definite shape Definite volume Particles are vibrating and packed closetogether.
The particles do notflow.
Crystalline Solids
Particles are arranged in an organizedpattern.
Example: Diamond
Amorphous Solids
Particles are not organized in an orderly fashion.
Example: Glass
Liquids
Indefinite shape Definite volume Liquids will take the shape of a container, but they maintain the same volume.
Particles are touching and packed close together. The higher energy allows the particles to move around each other.
Viscosity
A liquid’s resistance to flow.
Gases
Indefinite shape Indefinite volume Gases take the shape of a container. They also occupy the volume of the container no matter how big or small it is.
High energy motion
Plasma
High energy matter A common example is the sun. Super high energy gas particles that lostelectrons.
Plasma is the most common form of matter in the Universe.
States of Matter
Property Solid (s) Liquid (l) Gas (g)
Particle Spacing Close Close Great
Energy Low Medium High
Motion Low Medium High
Shape Definite Indefinite Indefinite
Volume Definite Definite Indefinite
Objective 2
Describe states of matter using the kinetic molecular theory.
Kinetic Molecular Theory
can explain the behavior of matter in its different states.
Kinetic Molecular Theory: Explains the states of matter based on the concept that the particles in all forms of matter are in constant motion.
Kinetic Energy: Energy an object has due to its motion.
Kinetic Energy and Kelvin TemperatureTemperature: the average kinetic energy of the particles in a material As particles are heated, they absorb energy, thus increasing their average kinetic energy and their temperature.
Motion stops at absolute zero (0 Kelvin). Kelvin temperature scale reflects the relationship between temperature and average kinetic energy. It is directly proportional.
Objective 3
Describe changes in states of matter with respect to kinetic energy and temperature.
Energy and Phase Changes
During a phase change, all energy goes to motion until phase change is done.
The temperature does not change until the phase change is done.
Melting
Solid Liquid
Example 1Example 2
Freezing
Liquid Solid
Example 1
Evaporation/Boiling
Liquid Gas
Example 1
Condensation
Gas Liquid
Example
Sublimation
Solid Gas
Example
Opposite of Sublimation? DepositionExample
Objective 4
Describe the different variables that define a gas.
Kinetic Theory of Gases
• Gases are mostly emptyspace.
• The molecules in a gas are separate, very small, and very far apart.
Kinetic Theory of Gases
• Gas molecules are in constant, chaotic motion.
• Collisions between gas molecules are elastic(there is no energy gain or loss).
Kinetic Theory of Gases
• The average kinetic energy of gas molecules is directly proportional to the absolute temperature.
• Gas pressure is caused by collisions of molecules with the walls of the container.
Behavior of Gases
• Gases have weight.
• Gases take up space.
• Gases exert pressure.
• Gases fill their containers.
Gases doing all of these things!
Variables that Describe a Gas• Volume: measured in L, mL, cm3 (1 mL = 1 cm3)
• Amount: measured in moles (mol), grams (g)
• Temperature: measured in Kelvin (K)K = ºC + 273
• Pressure: measured in mm Hg, torr, atm, etc. P = F / A (force per unit area)
Moderate Force (about 100 lbs)
Small Area (0.0625 in2)
Enormous Pressure (1600 psi)P = F /A
Bed of Nails
Large Surface Area (lots of nails)
Moderate ForceSmall Pressure
P = F / A
Units of Pressure• 1 atm = 760 mm Hg• 1 atm = 760 torr• 1 atm = 1.013 x 105 Pa• 1 atm = 101.3 kPa
Boyle’s Law
•As P, V and vice versa….
•Inverse relationship
P1V1 = P2V2
•For a given number of molecules of gas at a constant temperature, the volume of the gas varies inversely with the pressure.
Boyle’s Law and Kinetic Molecular TheoryHow does kinetic molecular theory explain Boyle’s
Law? Gas molecules are in constant, random motion.
Gas pressure is the result of molecules collidingwith the walls of the container.
As the volume of a container becomes smaller, the collisions over a particular area of container wall increase…the gas pressure increases!
Pressure‐Volume Calculations
Example: Consider the syringe. Initially, the gas occupies a volume of 8 mL and exerts a pressure of 1 atm.
What would the pressure of the gas become if its volume were increased to 10 mL?
Equation for Boyle’s Law
P1V1 = P2V2
where: P1 = initial pressureV1 = initial volume
P2 = final pressureV2 = final volume
P1V1 = P2V2
Using the same syringe example, just “plug in” the values:
P1V1 = P2V2
(1 atm) (8 mL) = (P2) (10 mL)
P1V1 = P2V2
(1 atm) (8 mL) = P2(10 mL)
P2 = 0.8 atm
Example: A sample of gas occupies 12 L under a pressure of 1.2 atm. What would its volume be if the pressure were increased to 3.6 atm? (assume temp is constant)
• P1V1 = P2V2
• (1.2 atm)(12 L) = (3.6 atm)V2
• V2 = 4.0 L
Example: A sample of gas occupies 28 L under a pressure of 200 kPa. If the volume is decreased to 17 L, what be the new pressure? (assume temp is constant)
• P1V1 = P2V2
• (200 kPa)(28 L) = (P2)(17 L)• P2 = 329 kPa
Temperature – Volume Relationships What happens to matter when it is heated?
It EXPANDS.
What happens to matter when it is cooled? It CONTRACTS.
Gas samples expand and shrink to a much greater extent than either solids or liquids.
Charles’ Law
2
2
1
1
TV
TV
•The volume of a given number of molecules
is directly proportional to the
Kelvin temperature.
•As T , V and vice versa….
•Direct relationshipVideo Clip 1,
Clip 2
Temperature – Volume Relationship
Doubling the Kelvin temperature of a gas doubles its volume.
Reducing the Kelvin temperature by one half causes the gas volume to decrease by one half…
WHY KELVIN? The Kelvin scale never reaches “zero” or has negative values.
Converting Kelvin
To convert from Celsius to Kelvin: add 273.
Example: What is 110 ºC in Kelvin?
110 ºC + 273 = 383 K
Converting Kelvin
To convert from Kelvin to Celsius:subtract 273.
Example: 555 K in Celsius?
555 K - 273 = 282 ºC
Example: A sample of nitrogen gas occupies 117 mL at 100.°C. At what temperature would it occupy 234 mL if the pressure does not change?
• V1 = 117 mL; T1 = 100 + 273 = 373 K• V2 = 234 mL; T2 = ???
• V1 / T1= V2 / T2
• T2 = 746 K
Example: A sample of oxygen gas occupies 65 mL at 28.8°C. If the temperature is raised to 72.2°C, what will the new volume of the gas?
• V1 = 65 mL; T1 = 28.8 + 273 = 301.8 K• V2 = ??? mL; T2 = 72.2 + 273 = 345.2 K
• V1 / T1= V2 / T2
• V2 = 74.3 mL
Temperature – Pressure Relationships
Picture a closed, rigid container of gas (such as a scuba tank) – the volume is CONSTANT.
What would happen to the kinetic energy of the gas molecules in the container if you were to heat it up?
How would this affect pressure?
Egg in a Bottle:!Video Clip
States of Matter Interactive
Temperature – Pressure Relationships Raising the Kelvin temperature of the gas will cause an INCREASE in the gas pressure.
WHY? With increasing temperature, the K.E. of the gas particles increases – they move faster!
They collide more often and with more energy with the walls of the container.
Top Related