Stoichiometry Molar Relationships in Chemical Reactions Sections 7

Stoichiometry Molar Relationships in Chemical Reactions Sections 7. 1 and 7. 2 - Homework Pg. 320 #1 -9 Pg. 324 #2, 3 Pg. 325 #2, 3, 5 -10

Stoichiometry: The study of proportions (ratios) in a chemical reaction

O 2 (g) + 2 H 2 (g) 2 H 2 O (g) Number of O 2 molecules Number of H 2 O molecules 1 2 25 6. 02 x 1023 = 1 mol 10 mol The ratio of the quantities of substances in the reaction is always the same.

Mole Ratio – The ratio of the moles of reactants or products in a chemical equation. • comes from the coefficients in the balanced equation O 2 (g) Mole ratio: + 2 H 2 (g) 2 H 2 O (g) O 2 : H 2 O 1 : 2

Calculations Involving MOLES Example 1: What amount of H 2 is produced when 5. 2 mol of ammonia decomposes? 2 NH 3 N 2 n NH 3 = 5. 2 mol Strategy: The molar ratio is provided in the balanced equation. Use it as a conversion factor! + 3 H 2 n H 2 = ? mol

Example 2: What amount of oxygen is required to produce 0. 25 mol of product? P 4 + 5 O 2 2 P 2 O 5

Practice! Page 319 #3 What amount of potassium is produced when 0. 15 mol of K 2 O decomposes? [0. 30 mol] 2 K 2 O 4 K + O 2

Calculations Involving MASS • balanced chemical equations give information about ratios of particles and moles • each substance has a different molar mass • equal masses of two different substances do not contain the same number of particles • the mole is the ONLY UNIT that links quantities in a reaction

n = m/M m=n*M gases – next unit) n = N/NA (for N = n * NA

Example 3: Calculate the mass of hydrogen needed to produce 15. 5 g of ammonia. N 2 + 3 H 2 m H 2 = ? g 2 NH 3 m NH 3 = 15. 5 g Strategy: (All paths go through Mole Island!) m NH 3 n NH 3 : n H 2 m. H 2 = 1. 441 mol H 2 x 2. 02 g/mol = 2. 91 g (to 3 SD)

Example 4: Determine the number of molecules of ammonia that are produced when 43. 5 g of nitrogen reacts with an excess of hydrogen. N 2 + 3 H 2 m N 2 = 43. 5 g Strategy: m N 2 n N 2: n NH 3 N NH 3 2 NH 3 N NH 3 = ? molecules

Practice! Page 323 #1 A typical antacid tablet contains 0. 50 g of calcium carbonate. The chemical equation for the neutralization of hydrochloric acid (stomach acid) with calcium carbonate is: Ca. CO 3 (s) + 2 HCl CO 2 (g) + H 2 O (l) + Ca. Cl 2 (aq) a) What mass of hydrochloric acid will this mass of calcium carbonate neutralize? [0. 36 g] b) Predict what mass of calcium chloride will be produced. [0. 55 g]

Homework • Pg. 320 #1 -9 • Pg. 324 #2, 3 • Pg. 325 #2, 3, 5 -10