* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Document
Safety data sheet wikipedia , lookup
Enantioselective synthesis wikipedia , lookup
Nuclear fusion wikipedia , lookup
Electrolysis of water wikipedia , lookup
Chemical potential wikipedia , lookup
Acid–base reaction wikipedia , lookup
Chemical industry wikipedia , lookup
Hypervalent molecule wikipedia , lookup
Computational chemistry wikipedia , lookup
Nucleophilic acyl substitution wikipedia , lookup
Asymmetric induction wikipedia , lookup
Multi-state modeling of biomolecules wikipedia , lookup
Supramolecular catalysis wikipedia , lookup
Hydrogen-bond catalysis wikipedia , lookup
Photoredox catalysis wikipedia , lookup
Biochemistry wikipedia , lookup
Chemical equilibrium wikipedia , lookup
Electrochemistry wikipedia , lookup
Ring-closing metathesis wikipedia , lookup
Marcus theory wikipedia , lookup
Strychnine total synthesis wikipedia , lookup
Discodermolide wikipedia , lookup
Thermometric titration wikipedia , lookup
Rate equation wikipedia , lookup
Physical organic chemistry wikipedia , lookup
Photosynthetic reaction centre wikipedia , lookup
Chemical reaction wikipedia , lookup
Petasis reaction wikipedia , lookup
Lewis acid catalysis wikipedia , lookup
George S. Hammond wikipedia , lookup
Click chemistry wikipedia , lookup
Transition state theory wikipedia , lookup
Process chemistry wikipedia , lookup
Chemical thermodynamics wikipedia , lookup
Chemistry 25 Chapter 8 Quantities in Chemical Reactions Global Warming z z z Scientists have measured an average 0.6 °C rise in atmospheric temperature since 1860. During the same period atmospheric CO2 levels have risen 25%. Are the two trends causal? 1 The Source of Increased CO2 z The primary source of the increased CO2 levels are combustion reactions of fossil fuels we use to get energy. • 1860 corresponds to the beginning of the Industrial Revolution in the U.S. and Europe. CH 4(g) + 2 O 2(g) → CO 2(g) + 2 H 2 O(g) 2 C8H18(l) + 25 O 2(g) → 16 CO 2(g) + 18 H 2O(g) Quantities in Chemical Rxns z The amount of every substance used and made in a chemical reaction is related to the amounts of all the other substances in the reaction. z Stoichiometry 2 Making Molecules Mole-to-Mole Conversions z The balanced equation is the “recipe” for a chemical reaction. 3 H2(g) + N2(g) → 2 NH3(g) z Since we count molecules by moles: Example z How Many Moles of NaCl Result from the Complete Reaction of 3.4 Mol of Cl2? 2 Na(s) + Cl2(g) → 2 NaCl 3 Practice z According to the following equation, how many moles of water are made in the combustion of 0.10 moles of glucose? C6H12O6 + 6 O2 → 6 CO2 + 6 H2O Making Molecules Mass-to-Mass Conversions z z z We know there is a relationship between the mass and number of moles of a chemical. 1 mole = Molar Mass in grams. The molar mass of the chemicals in the reaction and the balanced chemical equation allow us to convert from the amount of any chemical in the reaction to the amount of any other. 4 Example z How Many Grams of Glucose Can Be Synthesized from 58.5 g of CO2 in Photosynthesis? Practice z How Many Grams of O2 Can Be Made from the Decomposition of 100.0 g of PbO2? 2 PbO2(s) → 2 PbO(s) + O2(g) (PbO2 = 239.2, O2 = 32.00) 5 Representative for the Combustion of Fossil Fuel CH4[g] + 2 O2[g] → CO2[g] + 2 H2O[g] + energy Unfortunately … CH4[g] + 2 O2[g] → CO2[g] + 2 H2O[g] + energy 6 Limiting Reagent z The limiting reactant (or limiting reagent) • For example, bicycles require one frame and two wheels. If you have 20 wheels but only 5 frames, it is clear that the number of frames will determine how many bicycles can be made. z The theoretical yield of product Practice z Zinc metal reacts with hydrochloric acid by the following reaction. Zn(s) + __ HCl(aq) → ZnCl2(aq) + H2(g) – If 0.30 mol Zn is added to hydrochloric acid containing 0.52 mol HCl, how many moles of H2 are produced? 7 However Actual Yield z We may not get the maximum amount of product , theoretical yield. Because z Therefore, we will only obtain less product than theoretical yield • the actual yield. z Percent yield: 8 Review z Find Limiting Reagent z Calculate percent Yield Example z What Is the Limiting Reactant and Theoretical Yield When 0.552 Mol of Al React with 0.887 Mol of Cl2? 2 Al(s) + 3 Cl2(g) → 2 AlCl3 9 Practice z How Many Moles of Si3N4 Can Be Made from 1.20 Moles of Si and 1.00 Moles of N2 in the Reaction? More Practice z Three moles of 1-propanol, C3H7OH, reacts with one mole of phosphorus trichloride to produce 1-chloropropane, C3H7Cl, and phosphorus acid, H3PO3. What is the percent yield if you begin with 75.0 g of both 1propanol and phosphorus trichloride and obtain 1.0 mole of 1-chloropropane? (1propanol= 60.10 mg/mol, phosphorus trichloride= 137.33 mg/mol) 10 Measuring Amounts in the Lab z z In the lab, our balances do not measure amounts in moles, unfortunately, they measure amounts in grams. This means we must add two steps to each of our calculations: first convert the amount of each reactant to moles, then convert the amount of product into grams. Example z When 11.5 g of C Are Allowed to React with 114.5 g of Cu2O in the Reaction Below, 87.4 g of Cu Are Obtained. Cu2O(s) + C(s) → 2 Cu(s) + CO(g) 11 Practice z How Many Grams of N2(g) Can Be Made from 9.05 g of NH3 Reacting with 45.2 g of CuO? 2 NH3(g) + 3 CuO(s) → N2(g) + 3 Cu(s) + 3 H2O(l) If 4.61 g of N2 Are Made, What Is the Percent Yield? Enthalpy Change z We previously described processes • Exothermic: • Endothermic: z The enthalpy of reaction is the amount of thermal energy that flows through a process. • At constant pressure. • ΔHrxn 12 Sign of Enthalpy Change z For exothermic reactions, the sign of the enthalpy change is negative when: • Sign of Enthalpy Change z For endothermic reactions, the sign of the enthalpy change is positive when: 13 Enthalpy and Stoichiometry z The amount of energy change in a reaction depends on the amount of reactants. • z Writing a reaction implies that amount of energy changes for the stoichiometric amount given in the equation. Example z How Much Heat Is Associated with the Complete Combustion of 11.8 x 103 g of C3H8(g)? 14 Practice z How Much Heat Is Evolved When a 0.483 g Diamond Is Burned? (ΔHcombustion = −395.4 kJ/mol C) Vocabularies z z z z z Stoichiometry The limiting reactant (or limiting reagent) The theoretical yield Percent yield Exothermic/endothermic reactions 15