The Molar Volume of a Gas
Chemistry 117
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Videos
• Gas Laws and the Kinetic Molecular Theory:
http://www.cengage.com/chemistry/gochemi
stry_player/
• Combined Gas Law:
http://college.cengage.com/chemistry/discipli
ne/thinkwell/2852.html
Gas Laws
• Boyle’s Law: Pressure and volume are inversely
related. PV=constant
• Charles’s law: Volume and temperature are
directly related. V/T=constant
• Combined Law: P1V1 / T1 = P2V2 / T2
• Avogadro’s law: volume of a gas is proportional
to the number of moles of a gas present.
• Ideal Gas Law: PV=nRT
– R, the universal gas constant, does not change. Be
careful of units !
– R= 0.0821 L atm mol-1 K-1
Lab Procedures
Mg (s) +2HCl (l)  MgCl2(aq) + H2(g)
• We are interested in knowing
how much H2(g) was created
• Make sure you do this
experiment 3X
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Calculations
• Example: Number of moles of of sodium
dichormate (VI)
You have 6 g of sodium dichromate. How many
moles of sodium dichromate do you have?
MW: 298 g/mol
6 g / 298 g/mol = moles of sodium dichromate
(IV) = 0.020 moles
Calculations
• Example: CO2(g) + CaO (s)  CaCO3(s)
You have 5.5L of carbon dioxide. What mass of
calcium carbonate will form if you react the
carbon dioxide with excess CaO under STP?
MW CaCO3 = 100.1 g/mol
PV=nRT for Ideal Gases. Assume CO2 behaves as an
ideal gas at STP
V= nRT/ P= [1mol x (0.08206 L atm mol-1 K-1) x
(273.15 K)] / 1 atm = 22.41 L for an ideal gas at
STP
• 5.5 L CO2 x (1 mol CO2/ 22.41 L CO2) x (1 mol
CaCO3 / 1 mol CO2) x (100.1 g CaCO3 / 1 mol
CaCO3) = 24.6 g CaCO3