Chemical Reaction Stoichiometry Key

Chemical Reaction Stoichiometry Key 1. Propane (C3H8) undergoes combustion in air according to the following balanced equation: C3H8(g) + 5 O2(g)  3 CO2(g) + 4 H2O(g) a. How many molecules of CO2 will be formed when 25 molecules of C3H8 react? 25 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑒𝑠 𝐶3 𝐻8 × 3 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑒𝑠 𝐶𝑂2 = 75 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑒𝑠 𝐶3 𝐻8 1 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑒 𝐶3 𝐻8 b. How many moles of oxygen are needed to react with 12.5 mol of C3H8? 12.5 𝑚𝑜𝑙 𝐶3 𝐻8 × 5 𝑚𝑜𝑙 𝑂2 = 62.5 𝑚𝑜𝑙 𝑂2 1 𝑚𝑜𝑙 𝐶3 𝐻8 c. How many grams of C3H8 react with 500.0 grams of oxygen? 𝟓𝟎𝟎. 𝟎 𝑔 𝑂2 × 1 𝑚𝑜𝑙 𝑂2 1 𝑚𝑜𝑙 𝐶3 𝐻8 44.097 𝑔 𝐶3 𝐻8 = 𝟏𝟑𝟕. 𝟖03 = 137.8 𝑔 𝐶3 𝐻8 × × 32.00 𝑔 𝑂2 5 𝑚𝑜𝑙 𝑂2 1 𝑚𝑜𝑙 𝐶3 𝐻8 d. If a cylinder of propane contains 1.00 kg of C3H8, how many grams of CO2 are formed when it burns? 𝟏. 𝟎𝟎 𝑘𝑔 𝐶3 𝐻8 × 1000 𝑔 1 𝑚𝑜𝑙 𝐶3 𝐻8 3 𝑚𝑜𝑙 𝐶𝑂2 44.01 𝑔 𝐶𝑂2 = 𝟐𝟗𝟗4.08 × × × 1 𝑚𝑜𝑙 𝐶𝑂2 44.097 𝑔 𝐶3 𝐻8 1 𝑚𝑜𝑙 𝐶3 𝐻8 1 𝑘𝑔 = 2990 𝑔 𝑜𝑟 2.99 × 103 𝑔 𝐶𝑂2 e. How many moles of oxygen gas are required to form 5.25 x 1024 molecules of CO2? 𝟓. 𝟐𝟓 × 1024 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑒𝑠 𝐶𝑂2 × 5 𝑚𝑜𝑙 𝑂2 1 𝑚𝑜𝑙 𝐶𝑂2 = 𝟏𝟒. 𝟓348 × 6.02 × 1023 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑒𝑠 𝐶𝑂2 3 𝑚𝑜𝑙 𝐶𝑂2 = 14.5 𝑚𝑜𝑙 𝑂2 f. If 15.0 g of C3H8 are burned in excess oxygen gas, how many molecules of water will be formed? 𝟏𝟓. 𝟎 𝑔 𝐶3 𝐻8 × 1 𝑚𝑜𝑙 𝐶3 𝐻8 6.02 × 1023 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑒𝑠 𝐻2 𝑂 4 𝑚𝑜𝑙 𝐻2 𝑂 × × 1 𝑚𝑜𝑙 𝐻2 𝑂 44.097 𝑔 𝐶3 𝐻8 1 𝑚𝑜𝑙 𝐶3 𝐻8 = 𝟖. 𝟏𝟗1 × 1023 = 8.19 × 1023 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑒𝑠 𝐻2 𝑂 2. Suppose that 24.3 grams of solid calcium carbonate are decomposed with heat to produce solid calcium oxide and carbon dioxide gas. a. Write the decomposition reaction (remember to balance the equation and include state symbols) Δ CaCO3 (s)  CaO (s) + CO2 (g) b. How many grams of each product is formed? 𝟐𝟒. 𝟑 𝑔 𝐶𝑎𝐶𝑂3 × 𝟐𝟒. 𝟑 𝑔 𝐶𝑎𝐶𝑂3 × 1 𝑚𝑜𝑙 𝐶𝑎𝐶𝑂3 × 100.09 𝑔 𝐶𝑎𝐶𝑂3 1 𝑚𝑜𝑙 𝐶𝑎𝐶𝑂3 × 100.09 𝑔 𝐶𝑎𝐶𝑂3 1 𝑚𝑜𝑙 𝐶𝑎𝑂 1 𝑚𝑜𝑙 𝐶𝑎𝐶𝑂3 1 𝑚𝑜𝑙 𝐶𝑂2 1 𝑚𝑜𝑙 𝐶𝑎𝐶𝑂3 × × 56.08 𝑔 𝐶𝑎𝑂 1 𝑚𝑜𝑙 𝐶𝑎𝑂 44.01 𝑔 𝐶𝑂2 1 𝑚𝑜𝑙 𝐶𝑂2 = 𝟏𝟑. 𝟔 𝑔 𝐶𝑎𝑂 = 𝟏𝟎. 𝟕 𝑔 𝐶𝑂2 3. What mass of aluminum, in kg, is needed to react with 10.0 kg of chromium(III) oxide to produce chromium metal and aluminum oxide? The balanced chemical equation for this reaction is shown below. 2 Al (s) + Cr2O3 (s)  2 Cr (s) + Al2O3 (s) 1000 𝑔 𝟏𝟎. 𝟎 𝑘𝑔 𝐶𝑟2 𝑂3 × 1 𝑘𝑔 1 𝑚𝑜𝑙 𝐶𝑟 𝑂 2 𝑚𝑜𝑙 𝐴𝑙 2 3 × 152.00 𝑔 𝐶𝑟 × 1 𝑚𝑜𝑙 𝐶𝑟 𝑂 × 𝑂 2 3 26.98 𝑔 𝐴𝑙 2 3 1 𝑚𝑜𝑙 𝐴𝑙 × 1 𝑘𝑔 1000 𝑔 = 𝟑. 𝟓𝟓 𝑘𝑔 𝐴𝑙 4. When a hydrocarbon burns, water and carbon dioxide are produced. The density of gasoline is 0.79 g/mL. Assume that gasoline is completely made up of octane, C8H18. a. Write the balanced equation for the combustion of octane (remember state symbols): 2 C8H18 (l) + 25 O2 (g)  18 H2O (g) + 16 CO2 (g) b. Calculate the mass of water produced from the combustion of 2.0 L of gasoline. 𝟐. 𝟎 𝐿 × 1000 𝑚𝐿 1𝐿 × 0.79 𝑔 𝐶8 𝐻18 1 𝑚𝐿 × 1 𝑚𝑜𝑙 𝐶8 𝐻18 114.26 𝑔 𝐶8 𝐻18 18 𝑚𝑜𝑙 𝐻2 𝑂 8 𝐻18 × 2 𝑚𝑜𝑙 𝐶 × 18.02 𝑔 𝐻2 𝑂 1 𝑚𝑜𝑙 𝐻2 𝑂 = 𝟐. 𝟐 × 103 𝑔 𝐻2 𝑂 5. If 11.0 pounds of iron(III) oxide is reacted with excess carbon monoxide gas to yield solid iron ore and carbon dioxide gas, as shown in the balanced chemical equation below, how many grams of iron ore is produced? Fe2O3 (s) + 3 CO (g)  2 Fe (s) + 3 CO2 (g) 𝟏𝟏. 𝟎 𝑙𝑏 𝐹𝑒2 𝑂3 × 453.59 𝑔 𝐹𝑒2 𝑂3 1 𝑙𝑏 𝐹𝑒2 𝑂3 1 𝑚𝑜𝑙 𝐹𝑒 𝑂 2 𝑚𝑜𝑙 𝐹𝑒 2 𝑂3 2 3 × 159.70 𝑔 𝐹𝑒 × 1 𝑚𝑜𝑙 𝐹𝑒 𝑂 2 3 × 55.85 𝑔 𝐹𝑒 1 𝑚𝑜𝑙 𝐹𝑒 = 𝟑. 𝟒𝟗 × 103 𝑔 𝐹𝑒 6. Consider the following reaction between copper and oxygen gas: 2 Cu (s) + O2 (g) → 2 CuO (s) a) How many grams of Cu are required to react with 24.0 g of oxygen gas to form CuO? 𝟐𝟒. 𝟎 𝑔 𝑂2 × 1 𝑚𝑜𝑙 𝑂2 2 𝑚𝑜𝑙 𝐶𝑢 63.55 𝑔 𝐶𝑢 = 𝟗𝟓. 𝟑25 = 𝟗𝟓. 𝟑 𝒈 × × 1 𝑚𝑜𝑙 𝐶𝑢 32.00 𝑔 𝑂2 1 𝑚𝑜𝑙 𝑂2 b) How many grams of CuO will be formed? Total mass reactants = total mass products (Law of Conservation of Mass) so mass CuO = mass Cu + mass O2 = 95.3 + 24.0 = 119.3 g 7. A mixture of 60.0% ZnS and 40.0% CuS is heated in air until the sulfides are completely converted to oxides as shown by the following equations. 2 ZnS (s) + 3 O2 (g)  2 ZnO (s) + 2 SO2 (g) 2 CuS (s) + 3 O2 (g)  2 CuO (s) + 2 SO2 (g) How many grams of SO2 are produced from the reaction of 82.5 g of the sulfide mixture? 60.0 𝑔 𝑍𝑛𝑆 𝟖𝟐. 𝟓 𝑔 𝑚𝑖𝑥𝑡𝑢𝑟𝑒 × 100 𝑔 𝑚𝑖𝑥𝑡𝑢𝑟𝑒 × 𝟖𝟐. 𝟓 𝑔 𝑚𝑖𝑥𝑡𝑢𝑟𝑒 × 40.0 𝑔 𝐶𝑢𝑆 100 𝑔 𝑚𝑖𝑥𝑡𝑢𝑟𝑒 × 1 𝑚𝑜𝑙 𝑍𝑛𝑆 97.44 𝑔 𝑍𝑛𝑆 1 𝑚𝑜𝑙 𝐶𝑢𝑆 95.61 𝑔 𝐶𝑢𝑆 × × 2 𝑚𝑜𝑙 𝑆𝑂2 2 𝑚𝑜𝑙 𝑍𝑛𝑆 2 𝑚𝑜𝑙 𝑆𝑂2 2 𝑚𝑜𝑙 𝐶𝑢𝑆 32.5 g SO2 + 22.1 g SO2 = 54.6 g SO2 are produced. × 64.06 𝑔 𝑆𝑂2 1 𝑚𝑜𝑙 𝑆𝑂2 = 𝟑𝟐. 𝟓 𝑔 𝑆𝑂2 × 64.06 𝑔 𝑆𝑂2 1 𝑚𝑜𝑙 𝑆𝑂2 = 𝟐𝟐. 𝟏 𝑔 𝑆𝑂2