Unit 12: Stoichiometry Stoicheion = element Metron = to measure

A. Stoichiometry Chemists use balanced chemical equations to calculate how much reactant is needed or how much product is formed Provides same kind of quantitative information that a recipe does

B. Stoichiometry is… Calculation of the quantities of reactants and products in a chemical reaction The study of the quantitative relationships between the amounts of reactants and products in a chemical reaction Based on the Law of Conservation of Mass MASS and the NUMBER OF ATOMS are conserved in every chemical reaction

C. Interpreting Chemical Equations Chemical equations can be interpreted in terms of different quantities Number of atoms, molecules or particles Number of moles Mass Volume

Interpreting Chemical Equations Number of Atoms 12.1

Interpreting Chemical Equations Number of Molecules molecule N molecules H 2  2 molecules NH 3

Interpreting Chemical Equations Number of Molecules molecule N molecules H 2  2 molecules NH 3

Interpreting Chemical Equations Moles molecule N molecules H 2  2 molecules NH 3 1 mole N moles H 2  2 moles NH 3

Interpreting Chemical Equations Mass molecule N molecules H 2  2 molecules NH 3 1 mole N moles H 2  2 moles NH 3 28 g N x 2 g H 2  2 x 17 g NH 3

Interpreting Chemical Equations Mass molecule N molecules H 2  2 molecules NH 3 1 mole N moles H 2  2 moles NH 3 28 g N x 2 g H 2  2 x 17 g NH 3 34 g reactants  34 g products

D. Mole Ratios in Chemical Reactions The ratio between the coefficients of any two compounds in a balanced chemical reaction. Example: 4 Fe (s) + 3 O 2 (g)  2 Fe 2 O 3 (s)

Ch. 11 vs. Ch. 12 Ch. 11 – Converted amount of the same substance to different units Chapter 12 – determine amount of product made from given amount of reactant; determining how much reactant is needed to make a given amount of product.

Mole Map Volume Given Wanted ParticlesMolesMolesParticles GivenGivenWanted Wanted MassMass GivenWanted

Mole Map MassMolesMoles Mass GivenGivenWanted Wanted

E. Mole-Mole Conversions Given (moles of the given)# moles wanted = calculated moles of wanted # moles given MOLE RATIO USING COEFFICIENTS FROM CHEM. RXN. The mole ratio you use depends on what substance your given is (“given”) and which substance you want to calculate (“wanted”)

E. Mole – Mole Conversions Example Problem: If 2 moles of N 2 react with excess H 2, how many moles of NH 3 are produced? 1 N H 2  2 NH 3 Given: 2 moles N2 Wanted: __ moles NH3 Mole Ratio: moles “wanted” = 2 moles NH3 moles “given” 1 mole N 2

Mole-Mole Conversions - Example N H 2  2 NH 3 Given (moles of the given)# moles wanted = calculated moles of wanted # moles given MOLE RATIO USING COEFFICIENTS FROM CHEM. RXN. 2 moles N 2 2 moles NH 3 = 4 moles NH 3 1 mole N 2

1 N H 2  2 NH 3 Problem: If 2 moles of N 2 react with excess H 2, how many moles of NH 3 are produced?

Problem: If I have 8 moles of O 2 and excess H 2, how many moles of H 2 O can I make? “KNOWN” (given): “WANTED”: MOLE RATIO: Mole-Mole Conversions - Example 2 H O 2  2 H 2 O 8 moles O 2 moles H 2 O “wanted”

Mole-Mole Conversions - Example 2 H 2 + O 2  2 H 2 O Given (moles of the known) # moles wanted = calculated moles of wanted # moles known MOLE RATIO USING COEFFICIENTS FROM CHEM. RXN. 8 moles O 2 2 moles H 2 O = 16 moles H 2 O 1 mole O 2

Problem: If I have 8 moles of O 2 and excess H 2, how many moles of H 2 O can I make? Mole-Mole Conversions - Example 2 H O 2  2 H 2 O

Mole-Mole Calculations – You try… 4 Al + 3 O 2  2 Al 2 O 3 If I have 12 moles of Al 2 O 3 how many moles of O 2 do I need?