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## Molar Volume

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### Molar Volume Chem 11 Adv Gas Pressure: Pressure is defined as the force exerted on an object per unit of surface area (P = F/A) The pressure of a gas is determined by ... – PowerPoint PPT presentation

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Title: Molar Volume

1
Molar Volume

2
Gas Pressure
• Pressure is defined as the force exerted on an
object per unit of surface area (P F/A)
• The pressure of a gas is determined by the motion
of its particles
• Gases take the up the space of their container
• Particles move randomly through out the space of
the container colliding with each other and the
sides of the container, give a net equal pressure
through out

3
Gas Pressure
4
STP (review)
• Scientists have designated standard conditions
which allow them to compare different gas volumes
meaningfully
• Temperature 0 degrees Celsius or 273 Kelvin
(freezing point of water)
• Pressure 101.3 kPa (average atmospheric
pressure at sea level) or 1 atm

5
Joseph Louis Gay-Lussac
• Measured the volume of gases before and after
reactions

6
Law of Combining Volumes
• When gases react, the volume of reactants and
products, measure at equal temperature and
pressure are always in whole number ratios

7
• He realized that the number of molecules of gas
present corresponded to the volume ratios
• Hypothesis Equal volumes of gas at the same
temp and press contain the same number of
molecules

8
n1 n2 V1 V2
• n number of moles
• V volume
• Molar volume (MV) V/n
• (Units L/mol)

9
Standard Molar Volume
• Molar volume of a gas is the space occupied by
one mole of gas at STP
• Molar volume at STP is 22.4L/mol (ideal gases)
• Table examples of real gases, still very close!

Gas Molar Volume (L/mol)
Helium, He 22.398
Neon, Ne 22.401
Argon, Ar 22.410
Hydrogen, H2 22.430
Nitrogen, N2 22.413
Oxygen, O2 22.414
Carbon dioxide, CO2 22.414
Ammonia, NH3 22.350
10
Example
• What is the volume of 3.0 mol of NO2 at STP?
• We know that 1.0 mol occupies 22.4L !
• n1 n2
• V1 V2
• 1.0 mol 3.0 mol
• 22.4 L V2
• V2 3.0 x 22.4
• 1.0
• V2 67 L NO2

11
Example
• You have 44.8L of methane gas (CH4) at STP. How
many moles are present? How many grams?
• n1 n2
• V1 V2
• 1.0 mol n2____
• 22.4 L 44.8L
• V2 1.0 x 44.8
• 22.4
• n2 2.00 mol CH4
• X g CH4 2.00 mol x 16.04 g 32.08 g CH4
• 1 mol

12
Try it!
• Pg 73 38-43
• Extra Pg 74 1-6

13
Mole to Mole In class Assignment
• The average human requires 120.0 grams of glucose
per day. How many grams of CO2 (in the
photosynthesis reaction) are required for this
amount of glucose? The photosynthetic reaction
is 6 CO2 6 H2O ---gt C6H12O6 6 O2
• Given the following equation
• 8 Fe S8 ---gt 8 FeS
• What mass of iron is needed to react with 16.0
grams of sulfur?
• How many grams of FeS are produced?