Kinetic Theory and Gases
Kinetic Theory and Gases
Objectives
• Use kinetic theory to understand the concept of temperature.
• Be able to use and convert between the Celsius and Kelvin temperature scales.
Kinetic Theory
kinetic theory: all matter is made of particles (atoms,ions, molecules) that are in constant, random motion
kinetic energy (or KE): theenergy of motion; depends on both the mass and speed of the moving particles
temperature (T): a measure of the average KE of allthe particles in a substanceNOT T-E-M-P !
Kinetic Energynu
mbe
r of
parti
cles
Kelvin Scaleabsolute zero: the coldest possible T; there is no molecular motion; KE = 0(= -273oC or 0 Kelvin)
K = oC + 273 oC = K - 273
Kelvin temperature is directly proportional to the KE!
0 oC ≠ 0 KE 0 K = 0 KE200K has 2X more KE than 100K
KE
T
Objectives
• Understand the concept of atmospheric pressure.
• Be able to explain how a barometer works.• Be able to convert between pressure
measurements.
Gases and Pressure
pressure: force applied over an area
PF
A metric pressure unit:
1 pascal (Pa) = 1 N/m2
barometer: instrument that measures atmospheric pressure
Atmospheric pressure is 14.70 lbs/in2 at sea level. spheres DEMO!
Gases exert pressure by collisions.
Pressure Conversions
What is the current pressure in kPa and atm?
standard pressure (P)= 14.70 psi = 760.0 mm Hg = 29.92 in Hg = 101.3 kPa= 1.000 atm
standard temperature (T)= 0oC or 273 KSTP: standard T and P
CAN SMASH
• Have about 1 inch of water in the bowl plus at least one large ice cube.
• Remove tab from rinsed can. Place about 1/8” of water in the can.
• Hold can with tongs—palm up!• Heat the water over the burner, shaking can
regularly. Allow water to boil—steam forms. • Shake out any excess water. Heat briefly again.• Plunge top of can into the ice water!
Objectives
• Be able to use the pressure equation to explain pressure, temperature, and volume changes in gases.
• Understand how to solve word problems using the “GUESS” method.
• Be able to use the various gas laws to solve problems.
The G-U-E-S-S Method
• G = list the “given” values• U = list the “unknown”• E = find the correct equation• S = solve for the unknown (use algebra!)• S = substitute the values and solve
Boyle’s Law
PF
A
Boyle’s Law (T is constant )
• force (F) relates to temperature (T)• area (A) relates to volume (V)
P and V are inversely proportionalP V k
P V P V
1 1 2 2
temperature(in K scale)
volume
At constant temperature, 7.5 L of air at 89.6 kPa is compressed to 2.8 L. What is the new pressure?
Demo: balloon in vacuum
Charles’s Law and the P-T LawCharles’s Law (P is constant )V
Tk
V
T
V
T
1
1
2
2
V and T are directly proportional*must use Kelvin
P-T Law (V is constant )P
Tk
P
T
P
T
1
1
2
2
P and T are directly proportional*must use Kelvin
Demos: hot squirt bottle,space modulator gun
Gas Law Problems (use GUESS method)
(1) A 3.0 L balloon inside a -22oC freezer is removed and placed into a room at 19oC. What is the new volume if the pressure remains the same? What law was used?
(2) A solid container of gas at STP is heated and the pressure increases to 158 kPa. What is the new temperature of the gas? What law was used?
Objectives
• Understand how the various gas law equations are derived.
• Be able to use the ideal gas law, gas molar mass equation, and gas density equation to solve problems.
More Gas Laws
P V
n TR
P V n R T
P V
Tk
P V
T
P V
T
1 1
1
2 2
2
Mm
n
nP V
R T
Mm
Mm R T
P V
PVRT
Combined Gas Law
Ideal Gas Law
R = 8.31 kPaL/molK
n = # moles
Gas Molar Mass
Gas Density
DP M
R T
More Gas Law Problems1. What is the molar mass of a gas that has a mass
of 0.35 g and occupies 165mL at 95oC and 87.0 kPa?
2. How many moles of air are in a 3.2 L balloon under the current temperature and pressure conditions in this room?
3. What is the density of N2 gas at 95 kPa and 25oC?
Objectives
• Understand Avogadro’s law by considering the ideal gas law.
• Be able to use the law of combining gas volumes to solve simple gas stoichiometry problems.
• Be able to use the ideal gas law to solve more complex gas stoichiometry problems.
Avogadro’s Law
Avogadro’s Law: equal volumes of gases at the sameT and P contain equal numbers of molecules (n)
O2 He CO2
Why? Look at theIdeal Gas Law!P V n R T
nP V
R T
Law of Combining Gas Volumes
N2(g) + 3H2(g) → 2NH3(g)
Coefficients can represent gas volumes if thereactants and products are at equal T and P.
1 vol. 3 vol. 2 vol. 1 L 3 L 2 L
How many liters of H2 are needed to completelyreact with 2.5 L N2? Assume same T and P.
Gas Stoichiometry
g A → mol A → mol B → g B
g A → mol A → mol B → L B (use V = nRT/P)
(1) How many liters of CO2 at 23oC and 89.5 kPa areformed when a 468 g container of C3H8 is burned?C3H8 + 5 O2 → 3 CO2 + 4 H2O(2) How many liters of H2 gas are formed when 0.25 gNa reacts with HCl at STP?2Na + 2HCl → H2 + 2NaCl