Gas Stoich Lecture 3Gas Stoichiometry

Ways We’ve Already Gotten In/Out of Moles

• Grams Moles• Can use the molar mass of the compound to do that

• Liters Moles• Can use molarity equation to solve for moles (into moles),

or solve for volume/molarity (out of moles)

Gas Stoichiometry

• Can now use the ideal gas law to get into/out of moles

• Into moles: PV = nRT

Can use gas information to solve for moles

Gas Stoichiometry

• Can now use the ideal gas law to get into/out of moles

• Out of moles: PV = nRT

After doing the mole ratio, can solve for a quantity of gas

Gas Stoichiometry• STP: 0°C and 1 atm = 760 mm Hg = 101.3 kPa

• If you are at STP (and ONLY if you are at STP) –• 1 mole = 22.4 L• Can use as a way to get in and out of moles too!

Same Steps for Stoichiometry

1. Get it into moles

2. Do the mole ratio

3. Get it out of moles

Gas Stoich Example 1 - together• Sodium bicarbonate is heated.

• How many grams of carbon dioxide are produced if 2.76 grams of solid sodium bicarbonate are heated?

Gas Stoich Example 2 – on your own• Sodium metal is added to water.

• If 43.2 mL of hydrogen gas are produced at 767 torr and 59°C in excess water, how many grams of sodium were reacted?

Gas Stoichiometry

• All of stoichiometry still in play!• Limiting reactants

• Excess reactants

• Theoretical yields

• Percent yield

• Using gas stoich to find % composition in unknown

• Etc……..

Gas Stoich Example 3 – A bit more complicated….

• Acetic acid reacts with solid sodium carbonate.

• 5.00 grams of sodium carbonate is added to 20.0 mL of 1.50 M acetic acid. What volume of CO2 is produced at 0.878 atm and 23°C?

Dalton Law of Partial Pressures

Ptotal = P1 + P2 + P3 +….

• The total pressure = the sum of all the partial pressures

We’ll do more with this later in the unit, just one application for now….

Application of Dalton’s Law of Partial Pressures

HUGE!

Collecting pressure over water

Pair

Pgas PH2O vapor

Application of Dalton’s Law of Partial Pressures• Collecting pressure over water

• Because the water level is equal, we can assume pressure inside is EQUAL to the pressure outside

• So …… Pair = Pgas + PH2O vapor solve for Pgas

• PH2O is temperature dependent can look up on chart

• Pair is barometric pressure can look up on weather station

Pair

Pgas PH2O vapor

Gas Stoichiometry Demo• Magnesium and hydrochloric acid……