# U NIT 8: M EASUREMENTS AND C ALCULATIONS IN CHEMISTRY – S TOICHIOMETRY II Dr. Chin Chu Chemistry River Dell High School.

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U NIT 8: M EASUREMENTS AND C ALCULATIONS IN CHEMISTRY – S TOICHIOMETRY II Dr. Chin Chu Chemistry River Dell High School

C HEMICAL R EACTIONS Nitrogen gas reacts with hydrogen gas to form ammonia gas.

C HEMICAL REACTIONS

S TOICHIOMETRY – GENERALIZED FORM

S TOICHIOMETRY II – E XAMPLE 1 Nitrogen gas reacts with hydrogen gas to form ammonia gas. How many grams of ammonia gas will be produced when 34.5 grams of hydrogen gas is completely reacted with excess of nitrogen gas?

S TOICHIOMETRY II – E XAMPLE 2 Nitrogen gas reacts with hydrogen gas to form ammonia gas. How many molecules of ammonia gas will be produced when 34.5 grams of hydrogen gas is completely reacted with excess of nitrogen gas?

S TOICHIOMETRY II – EXERCISE PROBLEMS How many grams of methane is needed to produce 36.4 grams of water in the following chemical reaction: CH 4 + 2O 2  CO 2 + 2H 2 O? How many grams of diphosphorus pentoxide will be produced when 12.6 grams of element phosphorus reacts with excess oxygen gas? 2Ag 2 O  4Ag + O 2, how many grams of metallic silver and oxygen gas will be produced when 3.27 grams of silver oxide are completely decomposed? The balanced chemical equation for a double-replacement reaction is: FeCl 3 (aq) + 3NaOH(aq)  Fe(OH) 3 (p) + 3NaCl(aq). What are the formula units of each reactant needed to produce 26.8 grams of Fe(OH) 3 precipitate?

S TOICHIOMETRY – ANSWERS How many grams of methane is needed to produce 36.4 grams of water in the following chemical reaction: CH 4 + 2O 2  CO 2 + 2H 2 O? [16.2 g(CH 4 )] How many grams of diphosphorus pentoxide will be produced when element phosphorus reacts with excess oxygen gas? [28.9 g(P 2 O 5 )] 2Ag 2 O  4Ag + O 2, how many grams of metallic silver and oxygen gas will be produced when 3.27 grams of silver oxide are completely decomposed? [Ag: 3.04 g; O 2 : 0.23 g] The balanced chemical equation for a double-replacement reaction is: FeCl 3 (aq) + 3NaOH(aq)  Fe(OH) 3 (p) + 3NaCl(aq). What are the formula units of each reactant needed to produce 26.8 grams of Fe(OH) 3 precipitate? [FeCl 3 : 1.51x10 -23 formula units, NaOH: 4.53x10 -23 formula units]

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