Stoichiometry

Stoichiometry Derived from 2 Greek words: stoicheion = element metro = measure Deals with the calculations of quantities of reactants and products in a chemical reactions.

Math Skills Check - Ratios Current exchange rate of CAD to USD $1 CAD = $0.77 USD If you’re going on vacation to New York and need $500 USD spending money in cash, how much CAD will you need to exchange?

Current exchange rate of CAD to GBP (British Pounds) $1 CAD = $0.71 GBP If you’re going on vacation to London, England and have $1800 CAD to exchange, how much money in GBP will you have?

The Haber Process A process used to make ammonia (NH3) Used in fertilizers Refrigerants Cleaning agents Fermentation

N2 (g) + 3H2 (g)  2 NH3 (g) 1 molecule N2 + 3 molecules H2  2 molecules NH3 2 molecule N2 + 6 molecules H2  4 molecules NH3 6.02 x 1023 molecule N2 + 1.806 x 1024 molecules H2  1.204 x 1024 molecules NH3 1 mol N2 + 3 mol H2  2 mol NH3

Molar Ratios Just like we created ratios for money conversions, we can create molar ratios for mole conversions. N2 (g) + 3H2 (g)  2 NH3 (g) If I have 3.5 mols of N2, how much H2 will I need to create ammonia?

Steps to Solving Stoichiometry Problems Write the balanced chemical equation Write the given and required quantities underneath the appropriate compound in the chemical equation. If required, convert mass to moles. Use molar ratios to find unknown quantity. If required, convert moles back to mass.

CO2 (g) + 2 LiOH (g)  Li2CO3 (g) + H2O (g) Example 1 Lithium hydroxide has been used by astronauts, while in their space suits, to absorb the carbon dioxide that they exhale. If an astronaut exhales approximately 1.00 x 103 g of CO2 (g) in one day, how many grams of LiOH (g) is required to absorb the CO2 (g)? CO2 (g) + 2 LiOH (g)  Li2CO3 (g) + H2O (g)

Example 2 Air bags must inflate in less than a second. The effectiveness of air bags is based on the rapid conversion of a small amount of sodium azide (NaN3) into a large volume of nitrogen gas. (The other product that is formed is solid sodium.) The gas fills up an air bag, preventing the driver and passengers from incurring any life threatening injuries. How much nitrogen gas is produced if a standard airbag contains 0.130 g of sodium azide?