Slide 1 / 31 Slide 2 / 31 New Jersey Center for Teaching and Learning AP Chemistry Progressive Science Initiative This material is made freely available at www.njctl.org and is intended for the non-commercial use of students and teachers. These materials may not be used for any commercial purpose without the written permission of the owners. NJCTL maintains its website for the convenience of teachers who wish to Unit 3: Presentation B make their work available to other teachers, participate in a virtual professional learning Chemical Reactions and community, and/or provide access to course materials to parents, students and others. Stoichiometry Click to go to website: www.njctl.org www.njctl.org Slide 3 / 31 Slide 4 / 31 Chemical Reactions Chemical Reactions and Stoichiometry The world is full of chemical reactions. They power our batteries, To review, all chemical reactions must obey the law of conservation of allow us to see, and make nice red paint for sports cars! mass - they must be "balanced". light 3H 2 (g) + N 2 (g) --> 2NH 3 (g) Reactants Products 6 H atoms 6 H atoms cis-retinal trans-retinal 2 N atoms 2 N atoms The conversion of cis-retinal to trans-retinal is the first step of many that allows us to see. This supports the Bohr notion that atoms are simply rearranged in a chemical reaction, not created or destroyed. Nuclear reactions do "destroy" atoms as we shall see but still obey the law of conservation of mass Slide 5 / 31 Slide 6 / 31 Chemical Reactions Chemical Reactions When balancing a reaction, only the coefficients may be changed as Make sure to write the correct formulas of reactants and products changing the subscripts changes the nature of the material itself. NH 4 CO 3 --> NH 3 + CO 2 + H 2 O H 2 (g) + O 2 (g) --> H 2 O(g) Incorrect formula makes balancing impossible One cannot balance the O atoms by making O 2 suddenly O! Singular O is not reacting here, O 2 gas is! (NH 4 ) 2 CO 3 --> 2NH 3 + CO 2 + H 2 O Instead, one must change the number of oxygen or water Correct formula makes things easy!! molecules that react. H 2 (g) + 1/2 O 2 (g) --> H 2 O(g)
Slide 7 / 31 Slide 8 / 31 Chemical Reactions Reaction Stoichiometry Fractions may be used as coefficients which can then be Coefficients represent the relative number of molecules, multiplied through by a number to get whole number coefficients. elements, or compounds involved in the reaction. 4 NaCl(s) + 2 H 2 O(g) + 2 SO 2 (g) + O 2 (g) --> 4 HCl(g) + 2 Na 2 SO 4 2 NaCl(s) + H 2 O(g) + SO 2 (g) + 1/2 O 2 (g) --> 2 HCl(g) + Na 2 SO 4 4 moles of NaCl(s) produce 2 moles of Na 2 SO 4 To get whole number coefficients, multiply all 0.1 moles of NaCl(s) produce ______ moles Na 2 SO 4 coefficients by 2! 4.5 x 10 23 formula units NaCl(s) produce ___________ formula units Na 2 SO 4 4 NaCl(s) + 2 H 2 O(g) + 2 SO 2 (g) + O 2 (g) --> 4 HCl(g) + 2 Na 2 SO 4 *Note, the coefficients DO NOT represent the mass ratios - ie. 4 grams of NaCl will NOT produce 4 grams of HCl. Slide 9 / 31 Slide 10 / 31 Reaction Stoichiometry 1 What is the proper coefficient in front of the oxygen molecule after the following equation is balanced? Coefficients can be used to determine the relative amounts of substances involved in a reaction. NH 3 (g) + O 2 (g) --> NO(g) + H 2 O(l) 4 NaCl(s) + 2 H 2 O(g) + 2 SO 2 (g) + O 2 (g) --> 4 HCl(g) + 2 Na 2 SO 4 Answer How many grams of oxygen would be needed to produce 3 moles of HCl(g)? 3 moles of HCl x 1 mol O 2 x 32 g O 2 = 24 g O 2 4 mol HCl 1 mol O 2 molar ratio from balanced equation Slide 10 (Answer) / 31 Slide 11 / 31 1 What is the proper coefficient in front of the oxygen 2 The fermentation of sugar produces ethyl alcohol and molecule after the following equation is balanced? carbon dioxide gas. How many moles of carbon dioxide would be produced from the fermentation of 0.4 mol of glucose? NH 3 (g) + O 2 (g) --> NO(g) + H 2 O(l) C 6 H 12 O 6 (s) --> C 2 H 5 OH + CO 2 Answer 2.5 or whole number = 5 Answer [This object is a pull tab]
Slide 11 (Answer) / 31 Slide 12 / 31 2 The fermentation of sugar produces ethyl alcohol and 3 What is the sum total of coefficients when the equation carbon dioxide gas. How many moles of carbon dioxide below is balanced and all coefficients are simplified to the would be produced from the fermentation of 0.4 mol of lowest whole number ratio? glucose? C 6 H 12 O 6 (s) --> C 2 H 5 OH + CO 2 C 2 H 5 NH 2 + O 2 --> CO 2 + N 2 + H 2 O Answer Answer 0.8 moles [This object is a pull tab] Slide 12 (Answer) / 31 Slide 13 / 31 3 What is the sum total of coefficients when the equation 4 Given the UNBALANCED reaction below, determine how below is balanced and all coefficients are simplified to the many L of nitrogen gas would be produced when 110 lowest whole number ratio? grams of NaN 3 decompose completely @STP? NaN 3 (s) ---> Na(s) + N 2 (g) C 2 H 5 NH 2 + O 2 --> CO 2 + N 2 + H 2 O A 22.4 L B 44.8 L Answer Answer 43 C 33.1 L D 57.2 L E 11.2 L [This object is a pull tab] Slide 13 (Answer) / 31 Slide 14 / 31 4 Given the UNBALANCED reaction below, determine how 5 Phosphorus pentachloride decomposes into phosphorus many L of nitrogen gas would be produced when 110 trichloride gas and chlorine gas. How many total moles of grams of NaN 3 decompose completely @STP? gas will be produced after 50% of a 414 gram sample of phosphorus pentachloride decomposes? NaN 3 (s) ---> Na(s) + N 2 (g) A 22.4 L A 0.5 moles B 44.8 L Answer B 1.0 moles Answer C 33.1 L D C 1.5 moles D 57.2 L D 2.0 moles E 11.2 L [This object is a pull tab] E 3.0 moles
Slide 14 (Answer) / 31 Slide 15 / 31 5 Phosphorus pentachloride decomposes into phosphorus 6 If a 20 mL solution of 0.3 M Ca(NO 3 ) 2 were mixed with a trichloride gas and chlorine gas. How many total moles of solution of 3 M NaOH, how many mL of the 3 M NaOH gas will be produced after 50% of a 414 gram sample of solution would be needed to react with all of the calcium phosphorus pentachloride decomposes? ions? Ca 2+ (aq) + 2OH - (aq) --> Ca(OH) 2 (s) A 0.5 moles Answer B 1.0 moles D Answer C 1.5 moles D 2.0 moles [This object is a pull tab] E 3.0 moles Slide 15 (Answer) / 31 Slide 16 / 31 Reaction Stoichiometry 6 If a 20 mL solution of 0.3 M Ca(NO 3 ) 2 were mixed with a solution of 3 M NaOH, how many mL of the 3 M NaOH solution would be needed to react with all of the calcium The theoretical yield is the anticipated amount of product that ions? should be made based on the amounts of reactants used and reaction conditions. Ca 2+ (aq) + 2OH - (aq) --> Ca(OH) 2 (s) CaCO 3 (s) --> CO 2 (g) + CaO(s) What is the theoretical yield of CaO (in moles) if 200 grams of Answer 4 mL calcium carbonate completely decompose? 200 g CaCO 3 x 1 mol CaCO 3 x 1 mol CaO = 2 mol CaO 100 g CaCO 3 1 mol CaCO 3 [This object is a pull tab] Slide 17 / 31 Slide 18 / 31 Reaction Stoichiometry Reaction Stoichiometry Steps When two or more reactants are present, the reactant that is STEP 1: Convert known quantities to moles used up first (the limiting reactant) will determine the theoretical yield of product. N 2 (g) + 3H 2 (g) --> 2NH 3 (g) N 2 (g) + 3H 2 (g) --> 2NH 3 (g) If 44.8 L of nitrogen gas reacts with 44.8 L of hydrogen gas @STP, what is the theoretical yield of ammonia? If 44.8 L of nitrogen gas reacts with 44.8 L of hydrogen gas @STP, what is the theoretical yield of ammonia? 44.8 L N 2 (g) = 2 mol N 2 (g) 44.8 L H 2 (g) = 2 mol H 2 (g) This type of problem can be easily solved via a series of steps. One might think that since both reactants are found in the same quantities, we would run out of both at the same time. Why is this not true for this reaction?
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