Chapter 11 and supplemental Ms. Lockhart Chemistry Stoichiometry Chapter 11 and supplemental Ms. Lockhart Chemistry

Stoichiometry Importance By understanding the mole we can use the information to Predict mass or volume of a product. Predict how much reactant is needed for a reaction. Make substances of all kinds like Your sneakers Glue Your clothes Gum Candy Petrochemicals (oils, vaseline, gas)

Other uses % by mass (% composition) Empirical Formula Formula of a Hydrate Stoichiometric calculations Limiting Reagent % yield

Stoichiometry You can interpret a lot from a balanced chemical reaction. Iron is added to oxygen gas (O2) to yield iron (III) oxide (ferric oxide). 4 Fe + 3 O2  2Fe2O3 Atoms Moles Mass Total mass

Stoichiometry Nitrogen gas (N2) is added to hydrogen gas (H2) to make ammonia (NH3). N2 + 3 H2  2 NH3 Atoms Moles Mass Total mass

Practice Stoichiometry 3.00 g Magnesium (Mg) is heated with excess oxygen gas (O2) to make magnesium oxide. 2 Mg + O2  2 MgO

Steps to Stoichiometry Copy the word equation (write the chemical reaction in words). Write the word equation into a formula equation. Balance the chemical reaction. 2 Mg + O2  2 MgO

Steps to Stoichiometry Write given information under the balanced chemical reaction 2 Mg + O2  2 MgO 3.00 g

Steps to Stoichiometry Write what you are looking for. 2 Mg + O2  2 MgO 3.00 g ? O2

Steps to Stoichiometry Convert given information into moles. 2 Mg + O2  2 MgO 3.00 g ? O2 3.00 g Mg x 2 moles Mg = 3x2/24.31 = 0.2468 moles Mg 24.31 g Mg

Steps to Stoichiometry Use mole ratio to get moles to the correct representative particles. 2 Mg + O2  2 MgO 3.00 g ? O2 0.247 moles 0.247 moles Mg x 1 mole O2 = 0.247x1/2 = 0.124 moles O2 2 moles Mg

Steps to Stoichiometry Convert mole to grams, particles or whatever the answer ask for. Calculate and write the answer. 2 Mg + O2  2 MgO 3.00 g ? O2 0.247 moles 0.124 moles 0.124 moles O2 x 32 g O2 = 0.124x32/1 = 3.97 g O2 1 moles O2

Practice Stoichiometry Correct significant figures (sig figs) and rewrite the answer. 3.00 g Mg = 3 S.F. S.F. Answer: 3.97 g O2

Let’s Take It Slow…