Lecture 9 Notes

H2og molarmassofc3h8 44097gmol nc3h8 500g44097gmol

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Unformatted text preview: 2 H2O(g) ΔH° = −803.05 kJ CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(l) Enthalpy Changes for Chemical Reactions Calculate the heat generated when 500. g of propane burns in excess O2. C3H8(l) + 5 O2(g) 3 CO2(g) + 4 H2O(l) ΔH° = – 2220. kJ ΔH° = −890.36 kJ ΔH° is the standard enthalpy change P = 1 bar. T must be stated (if it isn’t, assume 25°C). ΔH° is a molar value. Burn 1 mol of CH4 with 2 mol O2 to form 2 mol of liquid water and release 890 kJ of heat Change a physical state, change ΔH° : H2O(l) vs. H2O(g) Molar mass of C3H8 = 44.097 g/mol. nC3H8 = (500. g) / (44.097 g/mol) = 11.34 mol C3H8 Since ΔH° = qp = –2220. kJ/(1 mol C3H8) q = (11.34 mol C3H8) (–2220. kJ / mol C3H8 ) = –2.52 x 104 kJ Bond Enthalpies Where Does the Energy Come From? Bond Enthalpy (bond energy) • Equals the strength of 1 mole of bonds • Always positive It takes E to break a bond Separated parts are less stable than the molecule. Less stable = higher E During a chemical reaction: Old bonds break: requires E (endothermic)...
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This note was uploaded on 03/02/2014 for the course CHEM 101 taught by Professor Multipleprofs during the Spring '07 term at Drexel.

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