Stoichiometry and the Math of Equations

Part 2: Mass-Volume

Objectives

• -Determine the molar relationships between reactants and products in a reaction equation

• -Use molar relationships and molar volume to convert between mass and volumes of components in a reaction

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Equations

• Equations are quantitative-there is a mathematical relationship between reactants and products

a) mass-mass problems b) mass-volume problems c) volume-mass problems d) volume-volume problems•

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Molar Volume

• Molar volume- the volume of 1 mole of ANY gas – Directly related to the number of gas

molecules – 1 mole of any gas contains the same

number of molecules (6.02 1023) so the volume of 1 mole of any gas is the same volume! 22.4 liters!

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Molar Volume• The volume of one mole is affected by

temperature and pressure changes– Assume we’re working under standard

conditions of temp and pressure, called STP, which is T =273 K (0° Celsius) and P =1 atm pressure

• Conversion factors: 22.4 liters OR 1 mole 1 mol 22.4 liters

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Molar Volume Problem #1• Mass – Volume• How many liters of hydrogen will

combine with 10.0 grams of oxygen to make water vapor?

• Steps(1) write and balance the equation (2) indicate the given and required (3) indicate the mole relationship

between the given and the required below the equation

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How many liters of hydrogen will combine with 10.0 grams of oxygen to

make water vapor?• Steps (1-3) ? L 10.0 g

2 H2 + O2 2 H2O

2 mole 1 mole? L H2 =• Step (4)10.0 g O2 x 1 mol O2 x 2 mol H2 x 22.4 L H2

1 32.0 g O2 1 mol O2 1 mol H2

= 14.0 L H2

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Molar Volume Problem #2

• Volume – Mass• How many grams of hydrogen will

combine with 15 liters of oxygen to make water vapor?

• Steps (1-3)

? g 15 L

2 H2 + O2 2 H2O

2 mole 1 mole8

How many grams of hydrogen will combine with 15 liters of oxygen to make

water vapor?

• Step (4)

? g H =

15L O2 x 1 mol O2 x 2 mol H2 x 2.02g H2 = 1 22.4 L O2 1 mol O2 1 mol H2

= 2.7 g H2

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Molar Volume Problem #3

• Volume-VolumeHow many liters of water vapor can be made if 5.0 liters of hydrogen combine with oxygen?Steps (1-3)

5.0L ? L2 H2 + O2 2 H2O

2 mole 2 mole10

How many liters of water vapor can be made if 5.0 liters of hydrogen combine

with oxygen?

• Step (4)

? L H2O =

5.0 L H2 x 1 mol H2 x 2 mol H2O x 22.4 L H2O

1 22.4 L H2 2 mol H2 1 mol H2O

= 5.0 L H2O11

Objectives

• -Determine the molar relationships between reactants and products in a reaction equation

• -Use molar relationships and molar volume to convert between mass and volumes of components in a reaction

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