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Reaction Stoichiometry Chapter 9 Notes Reaction Stoichiometry Problems Problem Type 1: Given and Unknown quantities are given in moles. Amount of given substance (in moles) → Amount of unknown substance (in moles) Reaction Stoichiometry Problems Problem Type 2: Given is an amount in moles and the Unknown is a mass in grams. Amount of given substance (in moles) → Amount of unknown substance (in moles) → Mass of unknown substance (in grams) Reaction Stoichiometry Problems Problem Type 3: Given is a mass in grams and the Unknown is an amount in moles. Mass of given substance (in grams) → amount of given substance (in moles) → amount of unknown substance (in moles) Reaction Stoichiometry Problems Problem Type 4: Given is a mass in grams and the Unknown is a mass in grams. Mass of given substance (in grams) → amount of given substance (in moles) → amount of unknown substance (in moles) → mass of unknown substance (in grams) Reaction Stoichiometry Problems Mole Ratio: conversion factor that relates the amounts in moles of any two substances involved in a chemical reaction. 2Al2O3 → 4Al + 3O2 2HgO → 2Hg + O2 4NH3 +6NO → 5N2 +6H2O Ideal Stoichiometry Calculations Conversions of Quantities in Moles In a spacecraft, the carbon dioxide exhaled by astronauts can be removed by its reaction with lithium hydroxide according to the following equation: CO2(g) + 2 Li(OH)(s) → Li2CO3(s) + H2O(l) How many moles of lithium hydroxide are required to react with 20 mol of CO2, the average amount exhaled by a person each day? Conversions of Quantities in Moles Ammonia, NH3, is widely used as a fertilizer and in many household cleaners. How many moles of ammonia are produced when 6 moles of hydrogen gas react with an excess of nitrogen gas? Conversions of Quantities in Moles The decomposition of potassium chlorate, K(ClO3), is used as a source of oxygen in the laboratory. How many moles of potassium chlorate are needed to produce 15 moles of oxygen? Conversions of Amounts in Moles to Mass In photosynthesis, plants use energy from the sun to produce glucose, C6H12O6, and oxygen from the reaction of carbon dioxide and water. What mass of glucose is produced when 3.00 moles of water react with carbon dioxide? Ideal Stoichiometry Calculations What mass of carbon dioxide is needed to react with 3.00 moles of H2O in a photosynthetic reaction? When magnesium burns in air, it combines with oxygen to form magnesium oxide. What mass of magnesium oxide is produced from 2.00 moles of magnesium? Conversion of Mass to Amounts in Moles The first step in the industrial manufacture of nitric acid is the catalytic oxidation of ammonia. NH3 + O2 → NO + H2O (not balanced) The reaction is run using 824g of NH3 and excess oxygen. How many moles of NO are formed? How many moles of H2O are formed? Conversion of Mass to Amounts in Moles Oxygen was discovered by Joseph Priestley in 1774 when he heated mercury (II) oxide to decompose it to form its constituent elements. How many moles of mercury (II) oxide are needed to produce 125g of oxygen? How many moles of mercury are produced? Mass to Mass Calculations Tin (II) fluoride is used in some toothpastes. It is made by the reaction of tin with hydrogen fluoride. How many grams of SnF2 are produced from the reaction of 30.00g of HF with Sn? Mass to Mass Calculations Laughing gas (N2O) is sometimes used as an anesthetic in dentistry. It is produced when ammonium nitrate is decomposed to form N2O and water. How many grams of NH4NO3 are required to produce 33.0g of N2O? How many grams of water are produced in this reaction? Mass to Mass Calculations When copper metal is added to silver nitrate in solution, silver metal and copper (II) nitrate are produced. What mass of silver is produced from 100.0g of Cu? What mass of aluminum is produced by the decomposition of 5.0 kg of Al2O3? Gas Stoichiometry You can apply the discoveries of Gay-Lussac and Avogadro to calculate the stoichiometry of reactions involving gases For gaseous reactants or products, the coefficients in chemical equations not only indicate mole ratios but also reveal volume ratios. 2 CO(g) + O2(g) → 2 CO2(g) Gas Stoichiometry Propane, C3H8, is a gas that is sometimes used as a fuel for cooking and heating. The complete combustion of propane occurs according to the following balanced equation. C3H8(g) + 5 O2(g) → 3 CO2(g) + 4H2O(g) What will be the volume, in liters, of oxygen required for the complete combustion of 0.350L of propane? Gas Stoichiometry C3H8(g) + 5 O2(g) → 3 CO2(g) + 4H2O(g) What will be the volume of carbon dioxide produced in the reaction? What volume of hydrogen gas is needed to completely react with 4.55 L of oxygen gas to produce water vapor? Gas Stoichiometry What volume of oxygen gas is needed to react completely with 0.626 L of carbon monoxide to form gaseous carbon dioxide? Nitric acid can be produced by the reaction of gaseous nitrogen dioxide with water: 3 NO2(g) + H2O(g) → 2 HNO3(l) + NO(g) If 708 L of NO2 gas react with water, what volume of NO gas will be produced? Gas Stoichiometry One mole of any gas takes up the same volume at the same temperature as one mole of any other gas. In order to make stoichiometric comparisons, chemists use Standard Temperature and Pressure when measuring Standard Molar Volume. At STP 1 mole of any gas occupies 22.4 Liters. Gas Stoichiometry What volume does 0.0685 mol of gas occupy at STP? What quantity of gas, in moles, is contained in 2.21 L at STP? At STP, what is the volume of 7.08 mol of nitrogen gas? A sample of hydrogen gas occupies 14.1 L at STP. How many moles of the gas are present? Limiting Reactants The limiting reactant is the reactant that is used up first. When the limiting reactant is gone, the reaction stops. The excess reactant is the reactant left after the limiting reactant is gone. It is analogous to making a cheese sandwich. Limiting Reactants Silicon dioxide is usually quite unreactive but reacts readily with hydrogen fluoride. SiO2(s) + 4HF(g) → SiF4(g) + 2H2O(l) If 6 mol HF is added to 4.5 mol SiO2, which is the limiting reactant? Limiting Reactants Some rocket engines use a mixture of hydrazine, N2H4, and hydrogen peroxide, H2O2, as the propellant. The equation is: N2H4(l) + 2H2O2(l) → N2(g) + 4H2O(g) Which is the limiting reactant in this reaction when 0.750 mol hydrazine is mixed with 0.500 mol hydrogen peroxide? Limiting Reactants N2H4(l) + 2H2O2(l) → N2(g) + 4H2O(g) How much of the excess reactant, in moles, remains unchanged? How much of each product, in moles, is formed? Limiting Reactants The black oxide of iron, Fe3O4, occurs in nature as the mineral magnetite. This substance can also be made in the laboratory by the reaction between red – hot iron and steam according to the following equation. 3Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g) When 36.0 g H2O is mixed with 67.0 g Fe, which is the limiting reactant? Limiting Reactants 3Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g) What mass in grams of black iron oxide is produced? What mass in grams of excess reactant remains when the reaction is complete? Limiting Reactants Zinc and sulfur, S8(s) react to form zinc sulfide. 8Zn(s) + S8(s) → 8ZnS(s) If 2.00 mol of Zn are heated with 1.00 mol of S8 identify the limiting reactant. How many moles of excess reactant remain? How many moles of the product are formed? Limiting Reactants Carbon reacts with steam to produce hydrogen and carbon monoxide. If 2.40 mol of carbon are exposed to 3.10 mol of steam, identify the limiting reactant. How many moles of each product are formed? What mass of each product is formed? Percentage Yield The theoretical yield is the maximum amount of product that can be produced from a given amount of reactant. The actual yield is the measured amount of a product obtained from a reaction. P. Y. = actual yield/theoretical yield x 100 Percentage Yield Chlorobenzene, C6H5Cl, is used in the production of many important chemicals, such as aspirin, dyes, and disinfectants. One industrial method of preparing chlorobenzene is to react benzene, C6H6, with chlorine. C6H6(l) + Cl2(g) → C6H5Cl(l) + HCl(g) When 36.8 g benzene react with an excess of Cl2, the actual yield of chlorobenzene is 38.8 g. What is the percentage yield of chlorobenzene? Percentage Yield Methanol can be produced through the reaction of CO and H2 in the presence of a catalyst. CO(g) + 2H2(g) → CH3OH(l) If 75.0 g of CO reacts to produce 68.4g CH3OH, what is the percentage yield of CH3OH? Percentage Yield Aluminum reacts with excess copper(II) sulfate according to the reaction below. If 1.85 g of aluminum react and the percentage yield of Cu is 56.6%, what mass of Cu is produced? Al(s) + CuSO4(aq) → Al2(SO4)3(aq) + Cu(s) (unbalanced)