General Chemistry Week Six Notes
General Chemistry Week Six Notes CHEM103090
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This 9 page Class Notes was uploaded by Nina Drachman on Tuesday October 13, 2015. The Class Notes belongs to CHEM103090 at University of Delaware taught by Graves PhD,Kimberly Susan in Fall 2015. Since its upload, it has received 56 views. For similar materials see General Chemistry in Health and Human Services at University of Delaware.
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Date Created: 10/13/15
Chemistry Lecture Oct 6 Chapter 4 Stoichiometry Applications Focus Question Nitrogen and Phosphorus in Fertilizers In addition to nitrogen provided by ammonia fertilizers often contain phosphorus and potassium compounds Often ammonia will be combined with a phosphorus source such as phosphoric acid to form a compound that provides both 3 NH3 H3PO4 NH43PO4 Reviewing the Haber Process Perhuman yearly totals N2g 1645 kg 3H2g 355 kg 2 NH3g 2000kg Given these amounts of reactants actual mass of NH3 produced is only 8 kg 0 Why 0 What does this mean for N2 and H2 actually used Theoretical and Actual Yield Theoretical yield the amount of product that would result if reagents fully reacted 2000 kg Actual yield the amount of product actually obtained from a reaction some of each reactant is left over 8 kg 0 Usually going to be lower than theoretical Percent Yield Theoretical yield amount of product that would result if reagents fully reacted as expected Actual yield amount of product actually obtained from a reaction some of each reactant is left over Yied actual yieldtheoretical yield x 100 When 355 kg of hydrogen is used 200 kg of ammonia could theoretically be made However only 800 kg is actually made What mass of hydrogen gas is actually needed to make 200 kg of ammonia 888 kg Possible Limits on Yield Nonideal conditions 0 Competing reactions One of our reactions is reacting with something else 0 Transfer issues Ex spilling a beaker Limited amounts of the reactants Limiting Reactant reagent Limiting reactant 0 Substance that is completely consumed in the chemical reaction 0 Determines the amount of product that can be formed during the reaction 0 Completely used up in the reaction Application to the Reaction 4NH3 502 n 6H20 4NO How many moles of N0 are produced if 4 moles NH3 are burned in 20 mol 02 o 4 moles of N0 are produced Which reactant is limiting o NH3 is limiting o 5 moles of 02 will be used so 15 moles of 02 will remain Oxygen is quotin excessquot Limiting Reactant with Moles Glucose is combusted according to the following unbalanced reaction C6H1206 lC02 H20 If 6 moles of oxygen and 6 moles of glucose are reacted what will be the limiting reactant 02 Practice 4NH3 502 n 6H20 4N0 How many grams of N0 are produced if 14 g NH3 are burned in 30 G 02 Which reactant is limiting How could we determine this Mass and Limiting Reactant 4NH3 502 n 6H20 4N0 How many grams of N0 are produced if 14 g NH3 are burned in 30 G 02 mol NH3 14 g NH3 x 1 mol NH3170 g NH3 82 mol NH3 mol 02 30 g 02 x 1 mol 02320 g 02 94 mol 02 Accounting for Reaction Stoichiometry 4NH3 502 D 6H20 4N0 Predict moles of product to compare 82 mol NH3 x 4 mol NO4 mol NH3 82 mol NO 94 mol 02 x 4 mol NO5 mol 02 75 mol NO Determining Final Mass 4NH3 502 n 6H20 4N0 How many grams of NO are produced if 14 g NH3 is burned in 30 G 02 75 mol NO x 300 g NOl mol NO 23 9 NO Conceptual Check The limiting reactant in a chemical reaction is onethat o Produces the smaller number of moles of product Chemistry Lecture Notes Chapter 4 Aqueous Reactions Focus Question Iron Rusting What reaction occurs when irons rusts Why is rust more common when iron is in contact with water Reactions Often Occur in Solution Reactions occur in solution because dissolved particles ions and molecules are oating freely and can easily interact Solvent carries the reactants into contact Types of Reactions Precipitationn strong ionion attraction between mixed reactants leading to solid formation Acidbasel H transfer between reactants Oxidationreduction redox electron transfer between reactants Reviewing Precipitation When solutions are mixed allowing ions to interact a precipitation occurs if one of the new possible combinations is insoluble Claq Agaq AgCls AgCl is precipitate Net ionic equation shows only ions that react with each other Using Solutions in Stoichiometry Measuring Lead in the Water Lead can occur dissolved in water as lead nitrate PbNO32 so to measure the amount you plan to form a precipitate by adding potassium phosphate K3PO4 What s the net ionic equation to describe this reaction 3Pb2 2PO43 Pb3PO42 If you obtain 0122g of lead phosphate from a 100mL sample what concentration in mM of lead ions did you have in the water 450 mM Pb2 Arrhenius Acids and Bases An Arrhenius acid is something that gives off H in solution 0 HCI aq l Haq Claq An Arrhenius base is something that generates 0H in solution 0 Na0H aq l Na aq 0Haq Strong Acids and Bases Strong acidsbases o Dissociate completely in aqueous solution ex strong electrolytes Strong acids HCIO4 HCI HBr Hl HN03 H2504 0 Strong acid ex 0 H2504aq 2Haq SO4aq Strong bases 0 Group 1A and group 2A hydroxides rst two columns 0 Ex NaOHaq Naaq 0Haq AcidBase Reactions Neutralization reaction that takes place when an acid reacts with a base and produces a solution of a salt in water Salt 0 Product of a neutralization reactions 0 Made up of the cation of the base plus the anion of the acid 0 Ex HCI Na0H NaCl H20 How many moles of water will be formed in the neutralization reactions of 1 mole of sulfuric acid H2504 with 1 mole of calcium hydroxide Acids are dangerous because of H Net Ionic View of AcidBase Reactions Soluble ionic compounds 0 HNO3aq NaOHaq l NaNO3aq HZO Total ionic equation 0 Haq NO3aq Naaq OHaq HZO Naaq NO3aq Net ionic equation Haq OHaq HZO Electron Transfer Reactions Electron transfer reactions are oxidationreduction or redox reactions 0 One or more e is transferred from one species to another Results in the generation of an electrical current Redox Reactions Redox reactions are easy to ID just look for changes in charge oxidation number 0 2Mgs 02g 2MgOs Need way to keep track of each atom s electrons in a compound whether ionic or molecular oxidation numbersstate Assigning Oxidation Numbers Prioritized list for assigning oxidation numbers 1 Oxidation numbers of atoms in a neutral compound sum to zero oxidation numbers of atoms in an ion sum to charge on the ion The oxidation number of a free element is always 0 The oxidation number of a manatomic ion equals the charge of the ion ex Cl Be2 4 The oxidation number of hydrogen is 1 in most compounds The oxidation number for uorine in all compounds in 1 The oxidation number of oxygen in most compounds is 2 7 The oxidation number of group IA and group A elements in a compound are 1 and 2 respectively DUN nuI Practice Assigning Oxidation Numbers Assign oxidation numbers to each elements in the following compounds the rst two are provided as examples What elements appear with different oxidation states on this list 502 l oxygen is 2 and sulfur is 4 CrO42 oxygen is 2 and chromium is 6 NH3 CIO3 SF6 Cl2 Understanding Redox Reactions Electron Transger Change in oxidation state results from gain or loss of electrons CH4g 2 02g C02g 2H20g LEO says GER Lose Electrons Oxidation Gain Electrons Reduction Which is a redox reaction Balancing Redox Reactions Copper wire immersed in silver nitrate solution 0 Cus 2Agaq Cu2aq 2Ags Can divide overall redox reaction into halfreactions Oxid Cus l Cu2aq 2e Red 2Agaq e l Ags HalfReaction Method Write separate reduction and oxidation halfreactions Balance number of particles in each halfreaction Balance charge by adding electrons to the appropriate side Multiply halfreactions by appropriate whole number to balance electrons Add halfreactions to generate a redox equation Practice Nas CuNO32aq D NaNO3aq Cus What is the balanced equation Which species is oxidized Which is reduced What is the oxidation halfreaction What is the reduction halfreaction How many electrons are transferred each time the reaction happens Rustron Oxidation Rust is essentially Fe203