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Do Now
• Why are gases considered fluids?
• Describe the particles in gas?
Ideal vs. Real gas
• The theory describes the behavior of an ideal gas.
• What does ideal mean?
• IDEAL GAS = an imaginary gas that obeys all G S
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the assumptions of the kinetic molecular theory (KMT)
• REAL GAS = an actual gas that does not behave completely according to the kinetic molecular theory (KMT)
Are gases attracted to each other?
Kinetic Molecular Theory (KMT)
• This theory is used to explain the properties of matter (solids, liquids, gases).
• It is based on the idea that particles are in constant random motion
constant, random motion.
• The theory can be used to explain the behaviors and the properties of gas molecules.
Ideal vs. Real gas
• There is no such thing as an ideal gas because real gases have mass and have attractions between them (intermolecular forces).
• Real gases have:
g
– Mass and volume
– Forces of attraction between them (intermolecular forces)
• IMF increase as the distance between them decreases
• The higher the molecular mass, the stronger the IMF
http://antoine.frostburg.edu/chem/senese/101
/liquids/faq/h‐bonding‐vs‐london‐forces.shtml
Kinetic Molecular Theory (KMT)
• 1. Gases consist of large numbers of tiny particles usually molecules (ex. CO2) or atoms (Ex. Ne), that are far apart relative to their size.
– Gases have an insignificant volume (almost zero) and the particles are separated from each other
and the particles are separated from each other by large distances.
• 2. Collisions between gas particles and between particles and the container walls are elastic collisions.
– Elastic collisions = no net loss of energy to the surrounds.
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Elastic vs. Inelastic collisions?
Kinetic Molecular Theory (KMT)
• 3. Gas particles are in constant, rapid, random motion. They travel in straight line paths and fill their containers. They possess kinetic energy which is energy of motion
energy, which is energy of motion.
Analogy: pool balls when hit travel
In straight line paths.
http://www.chm.davidson.edu/ChemistryApplets/KineticMolecularTheory/BasicConc
epts.html
Kinetic Molecular Theory (KMT)
• 4. Energy may be transferred between colliding particles. There is no net loss of energy as the result of these collisions. These collisions are perfectly elastic
collisions are perfectly elastic.
• 5. There are no forces of attraction or repulsion between gas particles.
Kinetic Molecular Theory (KMT)
• 6. The average kinetic energy of the gas particles depends on the temperature of the gas.
– Lower temperature = gas molecules have lower Lower temperature = gas molecules have lower
kinetic energy
– Higher temperature = gas molecules have higher kinetic energy
http://www.epa.gov/apti/bces/module1/kinetics/animation/kani1/kani104.htm
What properties of gases can be explained in terms of the KMT?
Review
• What does the KMT explain?
• Describe parts of the KMT.
1.
EXPANSION‐ Gases have no definite shape and no definite volume. 1.
2.
2.
3
3.
4.
5.
They expand to fill their container. Because of no attractions and constant motion
FLUIDITY‐ Gas particles glide past each other, this is because gases have insignificant attractive forces. LOW DENSITY Gases have low mass per unit volume. This is because gas LOW DENSITY‐
Gases have low mass per unit volume This is because gas
particles are so far apart from each other compared to their size.
COMPRESSIBILITY‐ The volume of a gas can be compressed into a much smaller volume. This is because gas particles are so far apart from each other.
DIFFUSION and EFFUSION
– DIFFUSION= the spontaneous mixing of gas particles even when the gas is not stirred.
– EFFUSION= the passing of gas particles through a tiny opening. This is because gas particles are in constant motion and there are insignificant attractions between them.
http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/animations/Effusion2.html
http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/flashfiles/gaslaw/micro_effusio
n.html
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Diffusion
Real vs. Ideal gas
• Real gases behave most like ideal gases under the following conditions:
– Low pressure
– High temperature
High temperature
Real vs. Ideal gas
• Why do real gases behave like ideal gases under high temperatures and low pressure?
• Under these conditions, gas particles are furthest apart from each other and have very
furthest apart from each other and have very weak forces of attraction (IMF) between them.
Real vs. Ideal gas
• What properties do some real gases have that allow them to behave like ideal gases?
• If a molecule is nonpolar = have symetry
• Does not weigh a lot
i h l
• Weak IMF
• Noble gases
Real vs. Ideal gas
• What makes real gases deviate from ideal gases?
• If a molecule is polar = assymetrical
• Weighs a lot
i h l
• Strong IMF
• Hydrogen bonding between molecules
• Dipole‐dipole attractions between molecules
Which of the following behave most like ideal gases and which deviate the most?
1.
2.
3.
4.
5.
6.
NH3 (g) _____
O2 (g) ______
He ______
H2O ______
N2 ______
Ne ______
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Gas Laws
• Gas laws are simple mathematical relationships between the volume, temperature and pressure of a gas.
• 1. VOLUME (V) – amount of space occupied by a sample of matter. Units = L, mL, cm3
– 1 mole = 22.4 L
– 1 mL = 1 cm3
• 2. TEMPERATURE (T) ‐ average kinetic energy of the particles in a sample of matter. Measured with a thermometer. ALWAYS USE KELVIN!
– K = C + 273
– 0 °C = ‐25 ° C= 100 ° C = • 3. PRESSURE (P) – Force per unit area on a surface. Force produced by the collision of gas particles with the container walls. Units = atm
Boyle’s Law
• Relates pressure and volume at a constant temperature.
• At a constant temperature, pressure varies inversely with volume
• Graph the pressure and volume relationship:
What type of relationship is this:
_________________________
P
V
• Formula: P1V1 =P2V2
• 1 = initial
• 2 = final
Boyle’s Law Example
Boyle’s Law Example
• A sample of oxygen gas has a volume of 150 mL when it’s pressure is 0.947 atm. What will the volume be at a pressure of 0.987 atm if the temperature remains constant?
the temperature remains constant?
• A gas has a pressure of 1.26 atm and occupies a volume of 7.40 L. If the gas is compressed to a volume of 2.93 L, what will its pressure be, assuming constant temperature?
assuming constant temperature?
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