Chem 1211 1st Edition Lecture 15Outline of Last Lecture I. Specific HeatII. State Functions and Changes of StateIII. Thermochemical EquationsOutline of Current Lecture I. Thermochemical equations continued Current LectureI. Thermochemical Equations Continueda. Thermochemical equations: balances chemical reaction plus the delta Hrxnb. C5H12 + 8 O2 5 CO2 + 6 H2O + 3523 kJc. Heat released during reaction (3523 kJ) assuming stoichiometric units are moles: 1 mole of C5H12 reacts with 8 moles of O2 to produce 5 moles of CO2, 6 moles of H2Od. Change in enthalpy (heat)e. Exothermic- heat producedf. ConcepTest: What is the enthalpy change for the first reaction?i. 2 C (s) + O2 (g) 2 CO (g) delta Hrxn=?ii. 2 CO (g) + O2 (g) 2 CO2 (g) delta Hrxn= -566kJiii. C (s) + O2 (g) CO2 (g) delta Hrxn= -393kJ1. ANSWER: -221 kJ2. Reasoning: a. Double everything in the third equation (gives you -786 kJ) b. Delta H1 + Delta H2 = Delta H3c. ? + -566 = -786d. ? = -220g. Example (Hess’s Law):i. A + B C delta H = xii. 2 A +2 B 2 C delta H = 2xThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.iii. .5 A + .5 .5C delta H = .5x1. C A +B delta H = -xh. Δ Hrxn= Σ n deltaH (products) – Σ n deltaH (reactants)i. n=stoichiometric coefficientsi. ConcepTest: Write the equation for the reaction of aluminum with oxygen to form Al2O3i. ANSWER: 4 Al (s) + 3 O (g) 2 Al2O3 (s)j. Bond- something that holds elements togetheri. When you break them, it costs energyk. ConcepTest: Calculate the enthalpy change for the reaction in which 30.0 g of aluminum reacts with oxygen to form Al2O3 at 25 degrees Celsius and one atmosphere:i. 4 Al (s) + 3 O (g) 2 Al2O3 (s) delta Hf (Al2O3) = -1676 kJ/molii. ANSWER: Use stoichiometry. Convert 30 grams of Al to 1.11 moles Al. It takes two moles of Al to get one mole of Al2O3 (according to the equation), so divide 1.11 by 2 to get .555 moles Al2O3. Multiply .555 by -1676 kJ/moles to get your answer (approx. -930.2 kJ)l. ConcepTest: For this reaction, which delta Hf values do we need from the table?i. C3H8 (g) + 5 O2 (g) 3 CO2 (g) + 4 H2O (l)1. Propane, CO2, and water (need to know all
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