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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 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

Gas Pressure

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

Joseph Louis Gay-Lussac

- Measured the volume of gases before and after

reactions

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

Along came Avogadro.

- 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

Avogadros Law

n1 n2 V1 V2

- n number of moles
- V volume
- Molar volume (MV) V/n
- (Units L/mol)

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

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

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

Try it!

- Pg 73 38-43
- Extra Pg 74 1-6

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?