Chapter 12 Stoichiometry

Stoichiometry Topics Conservation of mass and the balanced chemical equation Mole ratios in a chemical equation Stoichiometric calculations involving reactants and products Limiting Reactants Percent Yield

What is Stoichiometry? Stoichiometry is the study of quantitative relationships between amounts of reactants used and products formed by a chemical reaction.

Practical Applications of Stoichiometry In a spacecraft, the carbon dioxide exhaled by astronauts can be removed by its reaction with lithium hydroxide, LiOH, according to the following chemical equation. CO 2 (g) + 2LiOH(s) Li 2 CO 3 (s) + H 2 O(l) How many moles of lithium hydroxide are required to react with 20 mol of CO 2, the average amount exhaled by a person each day?

Strategy – Relate everything to the mole The mole is the common thread that links reactants to products. 1CO 2 (g) + 2LiOH(s) 1Li 2 CO 3 (s) + 1H 2 O(l) Mole Ratios

The Mole Super Highway Mole Mass Particles 1 mole = molar mass 1 mole = 6.02 x particles Mole Mass Particles 1 mole = molar mass 1 mole = 6.02 x particles MOLE RATIO

What mass of oxygen is needed to fully combust 12.5g ethane (C 2 H 6 )? Practice Problems How many moles of water are formed when 3.8 moles of Hydrogen react with an excess of Oxygen?

Limiting Reactants Why do reactions end? Some or all of the reactants get used up. Limiting Reactants limit the extent of the reaction and thereby determines the amount of the product. Leftover reactants are called excess reactants

How do you determine which reactant is limited? If 200g of sulfur reacts with 100g of chlorine, what mass of disulfur dichloride is produced? 1.Determine the moles of the reactants based on their masses. 2.Determine if the two reactants are in the correct mole ratio as given by the balanced chemical equation. 3.Use the number of moles of the limiting reaction as your given value to calculate the mass of the product that could be produced.

Pre-class Question 5/6 How many grams of iron are produced when 25 moles of Fe 2 O 3 react with 30 moles CO?

Percent Yield Stoichiometric calculations provide a theoretical yield or maximum amount of product that can be produced from a given amount of reactants. The actual yield is the amount that is actually produced when a reaction is carried out. The percent yield reflects the ratio of the theoretical and actual yields

Percent Yield Problem Ethanol (C 2 H 5 OH) is produced from the fermentation of sucrose. Determine the theoretical and percent yields of ethanol if 684g sucrose undergoes fermentation and 349g of ethanol are obtained.