Gases
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Gases
description
Gases. Chemistry Review. Atom – smallest piece of an element Molecule – smallest piece of a compound – two or more atoms chemically bonded Mole – counting number equal to 6.022 x 10 23 Molar Mass – number of grams of a substance per mole – equal to the atomic mass on the periodic table. - PowerPoint PPT Presentation
Transcript of Gases
Gases
Chemistry Review
Atom – smallest piece of an element Molecule – smallest piece of a compound –
two or more atoms chemically bonded Mole – counting number equal to 6.022 x 1023
Molar Mass – number of grams of a substance per mole – equal to the atomic mass on the periodic table
Review
How many moles in 5.5g of hydrogen gas? How many molecules in 2.5 moles of oxygen? What is the mass of one molecule of helium
gas?
Kinetic Theory
Matter is made of particles in continuous motion
Particles move in random directions at a variety of speeds
Particles of gases are on average very far apart from one another
Molecules of gases interact only when they collide
Collisions are perfectly elastic (no loss of kinetic energy)
Pressure Units
1atm = 760mmHg = 760torr = 101kPa
STP – standard temp and pressure (0°C and 1 atm)
Gas Laws
Volume is proportional to the temperature – Charles Law ( V1/T1 = V2/T2 )
Volume is inversely prop to temp – Boyles Law ( P1V1 = P2V2)
Pressure is prop to temp – Gay-Lussac’s Law ( P1/T1 = P2/T2 )
Combined Gas Law puts them together
( P1V1/T1 = P2V2/T2 )
Ideal Gas
One that follows all kinetic theory Volume of a gas also depends on the number
of moles Ideal Gas Law
PV = nRT R = .0821 L•atm/ mol•K
Examples
Determine the volume of 1.00 mole of a gas at STP.
A container of oxygen at STP has a volume of 10.0 L. What is the mass of the gas?
Examples
A helium party balloon has a radius of 18.0cm at 20°C and 1.05 atm. How many moles of He are in the balloon and what is the mass of the gas in the balloon?
An auto tire is filled to a pressure of 200kPa at 10°C. After driving 100km, the temp rises to 40°C. What is the pressure now?
Kinetic Energy of Molecules
The average KE of molecules is directly proportional to the temp
KE = ½ mv2 = 3/2 kT
k – Boltzman’s Constant = 1.38x10-23J/K
Example
What is the average KE of gas molecules at 37°C?
Average Velocity
Also called root mean square velocity vrms =
m – mass (in kg) of one molecule of the gas
3kT
M
Example
What is the rms speed of an oxygen molecule at 20°C?
