liquids and solids - bhs | ms. jensen chemistry€¦ · · 2018-01-24diffusion describes the...
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Unit 10.1
Pressure and temperature
Pressure
Pressure = Force/Area (N/m2= pascal)
-more force over same area = higher pressure
-more area with the same force = lower pressure
Atmospheric pressure=pressure of air in the Earth’s atmosphere.
Atmospheric pressure decreases as altitude increases.
Measuring Pressure
The first device for measuring atmosphericpressure was developed by Evangelista Torricelliduring the 17th century.
The device was called a “barometer”
Baro = weightMeter = measure
An Early Barometer
The normal pressure due to the atmosphere at sea level can support a column of mercury that is 760 mm high.
Standard Pressure
atomospheric pressure at sea level
1 standard atmosphere (atm) 101.3 kPa (kilopascals)- SI unit 14.7 lbs/in2
760 mm Hg (millimeters of mercury) 760 torr
Use standard pressure to convert between pressure units
The Kelvin Scale
Converting Celsius to Kelvin
Kelvins = C + 273
°C = Kelvins - 273
Unit 10.2
Properties of gases, liquids, and solids
Class starter
Covert the following
1. 56.1 torr to kPa
2. 780.0 torr to atm
3. 2.30 atm to mmHg
4. 45 ْC to Kelvin
5. 560 K to ْC
Kinetic Molecular Theory
1. pertaining to motion.
2. caused by motion.
3.characterized by movement: Running and dancing are kinetic activities.
ki⋅net⋅ic
Origin: 1850–55; < Gk kīnētikós moving, equiv. to kīnē- (verbid s. of kīneîn to move) + -tikos
Source: Websters Dictionary
Kinetic Molecular Theory of gases
Particles of matter are ALWAYS in motion
Volume of individual particles is zero.
Collisions of particles with container walls cause the pressure exerted by gas.
Particles exert no forces on each other.
Average kinetic energy is proportional to Kelvin temperature of a gas.
Properties of Gases
Gases expand to fill their containers
Gases are fluid – they flow
Gases have low density
1/1000 the density of the equivalent liquid or solid
Gases are compressible
Gases effuse and diffuse
Gases exert pressure on the walls of their containers
Kinetic Energy of Gas Particles
At the same conditions of temperature, all gases have the same average kinetic energy.
m = mass
v = velocity
2
2
1mvKE
At the same temperature, light moleculesmove FASTER than heavy molecules
Diffusion describes the mixing of gases. The rate of diffusion is the rate of gas mixing.
Diffusion is the result of random movement of gas molecules
The rate of diffusion increases with temperature
Small molecules diffuse faster than large molecules
Diffusion
Properties of liquids
Particles are closer together than gases and have more effective intermolecular forces than gases
lower kinetic energy than gases
High density
Relatively incompressible
Properties of liquids
• Surface tension- inward pull of molecules at the surface of a liquid which gives the liquid a “skin”
-liquids with stronger intermolecular forces have higher surface tension
Capillary action- attraction of the surface of a liquid to the surface of a solid. This attraction can pull a liquid against gravity.
Example: water moving up a paper towel, meniscus
chromatography uses capillary action to separate things
• Volatile liquids evaporate readily
• Nonvolatile liquids do not evaporate readily
• The weaker the intermolecular forces, the more volatile the liquid (easier to escape the surface of the liquid and evaporate)
Properties of solids
• Particles are closely packed with very effective intermolecular forces
• Very low kinetic energy
• High density – in general substances are most dense as a solid (exception: water )
• Relatively incompressible
Unit 10.3
Phase changes and Heating curves
Class starter 1. Which of the following will diffuse the fastest?
Ne at 20 ⁰C or Ne at 40 ⁰C
2. Which will diffuse the fastest?
Cl2 at 20 ⁰C or F2 at 20 ⁰C
3. In each pair, which molecule has the highest kinetic energy?
a. Ar at 30 ⁰C or Ne at 30 ⁰C
b. Ar at 30 ⁰C or Ar at 40 ⁰C
4. 40 ⁰C = _____K
5. Which liquid is more volatile? NH3 or CH4
Phase changes
Phase changes• Vaporization- liquid changes to a gas
– Evaporation: particles escape from the surface of a nonboiling liquid
– Boiling: change of a liquid to bubbles of vapor
Energy change in phase changes
• Exothermic: heat is released
- Freezing, condensation, deposition
– Feels warm around it, temperature increases
• Endothermic: heat is absorbed
– Melting, boiling, sublimation
– Feels cold around it, temperature decreases
kinetic energy tells how fast molecules are moving. (proportional to temperature)
Potential energy tells the potential the atoms have to bond.
-decrease potential energy - bonds are formed.
-increase potential energy – bond are broken
Heating curve
Heating curve explanations
• A positive slope shows that the temperature is increasing (Kinetic energy is increasing). Molecules are speeding up.
• When a substance melts or boils the temperature remains constant (kinetic energy stays the same) because all of the energy goes into breaking the intermolecular forces instead of speeding the molecules up. (potential energy increases)
Heating curve explanations
Molar heat of fusion ( ∆Hfus) : amount of energy needed to melt one mole of a solid
Molar heat of vaporization (∆Hvap) : amount of energy needed to vaporize one mole of a liquid
∆Hvap > ∆Hfus
Why? When vaporizing a substance all bonds need to be
broken, when melting a substance only some bonds are broken, most remain intact.
• Which of the following would you predict to have a higher heat of vaporization?
CH4 (nonpolar) or H2O (polar)
• H2O has stronger intermolecular forces so it would require more energy to pull them apart.
• Stronger intermolecular forces means higher heats of fusion and vaporization