Stoichiometry The Arithmetic of Equations Prentice-Hall Chapter 12.1 Dr. Yager

Objectives Explain how balanced equations apply to both chemistry and everyday situations. Interpret balanced chemical equations in terms of moles, representative particles, mass, and gas volume at STP. Identify the quantities that are always conserved in chemical reactions.

A balanced chemical equation provides the same kind of quantitative information that a recipe does.

Here is the Problem! Cupcake Recipe for 10 cupcakes: 2 eggs 3 cups of flour 1 cup sugar You have: 3 eggs 4 cups of flour 2 cups of sugar What limits the number of cupcakes you can make?

The original recipe is: 2:3:1 2 eggs, 3 C flour, 1 C sugar Given: 3 eggs, 4 C flour, 2 C sugar 3 eggs requires: 4.5 cups of flour and 1.5 cups of sugar 4 cups of flour requires: 2 2/3 eggs and 1 1/3 cups of sugar 2 cups of sugar requires: 4 eggs and 6 cups of flour The only one possible is #2!

The Chemist: Uses the ratio or balanced equation to calculate how much reactant is needed or product formed. The calculation of quantities in chemical reactions is a subject of chemistry called stoichiometry.

Stoichiometry Defined as the calculation of quantities in chemical reactions Form of bookkeeping for chemists Generally, one of the reactants limits the calculations

An equation can represent the manufacturing of a single tricycle.

A balanced chemical equation can be interpreted in terms of different quantities, including numbers of atoms, molecules, or moles; mass; and volume.

Interpreting Chemical Equations N2(g) + 3H2(g) 2NH3(g)

Atoms, Molecules, etc..

Moles

Mass

Volume

What is Conserved? Mass and atoms are conserved. Molecules, formula units, moles and volumes are not necessarily conserved. Example where they are conserved: H2(g) + I2(g) 2HI(g)

Balance and Tell What is Conserved C2H2 (g) + O2 (g) CO2 (g) + H2O(g) 2C2H2 (g) + 5O2 (g) 4CO2(g) + 2H2O(g) Atoms – Yes Mass - Yes Molecules – No Formula Units – No Moles – No Volume – No

1. A manufacturer of bicycles has 5350 wheels, 3023 frames, and 2655 handlebars. How many bicycles can be manufactured using these parts? 2675 bicycles 2655 bicycles 3023 bicycles 5350 bicycles

1. A manufacturer of bicycles has 5350 wheels, 3023 frames, and 2655 handlebars. How many bicycles can be manufactured using these parts? 2675 bicycles 2655 bicycles 3023 bicycles 5350 bicycles

2. A reaction that produces iron metal from iron ore: Fe2O3•H2O(s) + 3CO(g)  2Fe(s) + 3CO2(g) + H2O(g) What is the volume of gas at STP that reacts and the volume of gas at STP produced? 3 L and 4 L. 67.2 L and 89.6 L. 67.2 L and 67.2 L 3 L and 3 L

2. A reaction that produces iron metal from iron ore: Fe2O3•H2O(s) + 3CO(g)  2Fe(s) + 3CO2(g) + H2O(g) What is the volume of gas at STP that reacts and the volume of gas at STP produced? 3 L and 4 L. 67.2 L and 89.6 L. 67.2 L and 67.2 L 3 L and 3 L

3. What is conserved in this reaction? H2(g) + Cl2(g)  2HCl(g) only mass only mass and number of moles only mass, number of moles, and number of molecules mass, number of moles, number of molecules, and volume

3. What is conserved in this reaction? H2(g) + Cl2(g)  2HCl(g) only mass only mass and number of moles only mass, number of moles, and number of molecules mass, number of moles, number of molecules, and volume