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CHEM 1310
Sarrah Vakili

 Internal energy - based on work and q  State function - constant, only changes in terms of size Bond Energies  Energy required to break 1 mol of chemical bonds into the gaseous phase  Also known as bond enthalpy and bond dissociation energy  Will always be positive in value for the breaking of bonds o Break bonds - positive o Create bonds - negative  For reactions it may be: o Exothermic - stronger bonds in products then reactants - more stable products o Endothermic - stronger bonds in reactants then products Question: Estimate ∆E for the reaction: ethane + air → carbon dioxide + water Ie: combustion reaction Answer:  2C2H6 + 7O2 → 4CO2 + 6H2O  Note: CO2 energy for C-O is different then other C=O bonds  Bonds to break: o 6 C-H bonds o 1 C-C bonds o 7/2 O=O bonds  2 x 2 C=O bonds o 4 bonds total ∆ ∆ ∆ ∆ ∆ ∆  Ereacttants6 E (C-H) + 1 E(C-O) + 7/2 E(O=O) - [4 E(C=O) + 6 E(H-O)]  Look up values in the tables  ∆ E = [6 mol(414 kJ/mol) + 1 mol(347 kJ/mol) + 7/2(498 kJ/mol)] - [4 mols(799 kJ/mol) reactats + 6 mols(464 kJ/mol)] = -1406 kJ/mol o Expiremental = 1428 kJ Calorimetry  The isolated system used to determine quantities of heat where q reactionqcalormeter  2 types o Bomb calorimeter (qv, constant volume) - isolated network o Coffee cup calorimeter (qp, constant pressure) - closed system  P is ignored  Requires heat and water  ∆ E = qv + wv  C calpecific heat of calorimeter (total heat capacity) o -qcalormeter determined experimentally and the amount of heat required to raise the temperature of the calorimeter by 1ᵒ C  C calalibrate/find by a known standard or using a heater o Usually includes the center inside the calorimeter, especially if a coffee cup  Ie: you will need to find this  If not then qcalq bomb + qH2O Question: Chocolate chip cookies weighing 7.25 g are burnt in a bomb calorimeter to determine the energy content. The heat capacity of the calorimeter is 39.97 kJ/ᵒC. During combustion, the temperature of the water in the ca
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