© L.C.Lee 1997 Stoichiometry: Part 1: Mole Relationships in Chemical Equations

© L.C.Lee 1997 Review of the Mole Atoms are too small to count 1 by 1 Eggs are counted by 12’s (1 dozen) Atoms could be counted by 12’s Atoms are counted by a very large number: 602,000,000,000,000,000,000,000 OR: 6.02 X atoms = 1 mole

© L.C.Lee 1997 Formulas, atoms and the mole In a formula like CO 2, Subscripts tell quantity of atoms in single molecule/formula unit and also tell quantity of moles in one mole of compound.

© L.C.Lee 1997 Mole equivalents In a formula like CO 2, in one molecule CO 2, how many C atoms? how many O atoms? in one mole CO 2, how many moles of C? how many moles of O?

© L.C.Lee 1997 What’s in a formula? In a formula like KNO 3, in one unit KNO 3, how many K atoms? how many N atoms? how many O atoms? in one mole KNO 3, how many moles of K? how many moles of N? how many moles of O? in one mole KNO 3, how many moles of K + ? how many moles of NO 3 -1 ?

© L.C.Lee 1997 Mole-Mole Factors (ratios) Show the mole-to-mole ratio between two of the substances in a balanced equation Use the coefficients of two substances in the equation

© L.C.Lee 1997 Writing Mole Factors (ratios) 4 Fe + 3 O 2 2 Fe 2 O 3 Fe and O 2 4 mole Fe and 3 mole O 2 3 mole O 2 4 mole Fe Fe and Fe 2 O 3 4 mole Feand2 mole Fe 2 O 3 2 mole Fe 2 O 3 4 mole Fe O 2 and Fe 2 O 3 3 mole O 2 and 2 mole Fe 2 O 3 2 mole Fe 2 O 3 3 mole O 2

© L.C.Lee 1997 Learning Check S1 3 H 2 (g) + N 2 (g) 2 NH 3 (g) A. A mole ratio for H 2 and N 2 is 1) 3 mole N 2 2) 1 mole N 2 3) 1 mole N 2 1 mole H 2 3 mole H 2 2 mole H 2 B. A mole ratio for NH 3 and H 2 is 1) 1 mole H 2 2) 2 mole NH 3 3) 3 mole N 2 2 mole NH 3 3 mole H 2 2 mole NH 3

© L.C.Lee 1997 Solution S1 3 H 2 (g) + N 2 (g) 2 NH 3 (g) A. A mole factor for H 2 and N 2 is 2) 1 mole N 2 3 mole H 2 B. A mole factor for NH 3 and H 2 is 2) 2 mole NH 3 3 mole H 2

© L.C.Lee 1997 Chemical Calculations 4 Fe + 3 O 2 2 Fe 2 O 3 How many moles of Fe 2 O 3 are produced when 6.0 moles O 2 react? 6.0 mole O 2 x 2 mole Fe 2 O 3 = 4.0 mole Fe 2 O 3 3 mole O 2

© L.C.Lee 1997 Learning Check S2 4 Fe + 3 O 2 2 Fe 2 O 3 How many moles of Fe are needed to react with 12.0 mole of O 2 ? 1) 3.00 mole Fe 2) 9.00 mole Fe 3) 16.0 mole Fe

© L.C.Lee 1997 Solution S2 4 Fe + 3 O 2 2 Fe 2 O mole O 2 x 4 mole Fe = 16.0 mole Fe 3 mole O 2

© L.C.Lee 1997 Stoichiometry: Part 2: Mass Relationships in Chemical Equations

© L.C.Lee 1997 Mass - Mass Problem The reaction between H 2 and O 2 produces 13.1 g of water. How many grams of O 2 reacted? Write the equation H 2 (g) + O 2 (g)H 2 O (g) Balance the equation 2 H 2 (g) + O 2 (g)2 H 2 O (g)

© L.C.Lee 1997 Points to Remember 1. Read an equation in moles 2. Convert given amount to moles 3. Use mole factor to give desired moles 4. Convert moles to grams grams (given)grams (desired) moles (given)moles (desired)

Organize data: mole bridge ? g 13.1 g 2 H 2 (g) + O 2 (g)2 H 2 O (g) Plan g H 2 O mole H 2 O mole O 2 g O 2 Setup 13.1 g H 2 O x 1 mole H 2 O x 1 mole O 2 x 32.0 g O g H 2 O2 mole H 2 O 1 mole O 2 = 11.6 g O 2

© L.C.Lee 1997 Learning Check S 3 4 Fe + 3 O 2 2 Fe 2 O 3 How many grams of O 2 are needed to produce mole of Fe 2 O 3 ? 1) 38.4 g O 2 2) 19.2 g O 2 3) 1.90 g O 2

© L.C.Lee 1997 Solution S 3 2) 19.2 g O mole Fe 2 O 3 x 3 mole O 2 x 32.0 g O 2 2 mole Fe 2 O 3 1 mole O 2 = 19.2 g O 2

© L.C.Lee 1997 Learning Check S 4 How many grams of O 2 are need to react 50.0 grams of Na in the reaction 4 Na + O 2 2 Na 2 O Complete the set up: 50.0 g Na x 1 mole Na x ________ x _______ 23.0 g Na

© L.C.Lee 1997 Solution S 4 4 Na + O 2 2 Na 2 O 50.0 g Na x 1 mole Na x 1 mole O 2 x 32.0 g 23.0 g Na 4 mole Na 1 mole O 2 = g O 2

© L.C.Lee 1997 Learning Check S5 Acetylene gas C 2 H 2 burns in the oxyactylene torch for welding. How many grams of C 2 H 2 are burned if the reaction produces 75.0 g of CO 2 ? 2 C 2 H O 2 4 CO H 2 O

© L.C.Lee 1997 Solution S5 2 C 2 H O 2 4 CO H 2 O 75.0 g CO 2 x 1 mole CO 2 x 2 mole C 2 H 2 x 26.0 g C 2 H g CO 2 4 mole CO 2 1 mole C 2 H 2 = 22.2 g C 2 H 2

© L.C.Lee 1997 Pathways for Problems Using Equations Given (A) Find (B) grams (A)grams (B) moles (A) moles (B) particles (A)particles (B)

© L.C.Lee 1997 Pathways for Problems Using Equations Given (A) Find (B) grams (A)grams (B) molar molar mass (A) mass (B) coefficients moles (A) moles (B) Avogadro's Avogradro’s number number particles (A)particles (B)