CHEMICAL THERMODYNAMICS 1 chem 16 4 slides per page

Negative exothermic t is tfinal tinitial increase

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Unformatted text preview: reactant molecules (in case of reaction), and the solvent: surroundings heat hheat system Because the entire system is adiabatic: qsystem = 0 THEREFORE: qsystem = 0 The entire system is ADIABATIC qcalorimeter + qreaction + qwater = 0 Therefore: (qcalorimeter+ qwater) = – qreaction Heat Surroundings = - Heat System 9 1/7/2014 REMEMBER: (qcalorimeter+ qwater) = – qreaction For reactions: qcalorimeter = Ccal • ∆T qwater = mH2O • cH2O • ∆T qreaction = ∆Horeaction x nLR – ∆Horeaction is “negative”: EXOTHERMIC, ∴ ∆T is + (Tfinal > Tinitial ), Increase temperature (Ccal∆T + mH2OcH2O∆T) = -(∆Horeaction x nLR) − ∆T(C cal + m H 2O c H 2O ) n LR = ∆H rxn • Example: A coffee-cup calorimeter is used to determine the heat of reaction for the acid-base neutralization CH3COOH(aq) + NaOH(aq) → NaCH3COO(aq) + H2O(l) When we add 25.00 mL of 0.500 M NaOH at 23.000oC to 25.00 mL of 0.600 M CH3COOH initially placed in the calorimeter at the same temperature, the resulting temperature is observed to be 25.947oC. The heat capacity of the empty calorimeter has previously been determined to be 27.8 J/0C. Assume that the specific heat of the mixture is the same as that of water, 4.18 J/g0C and that the density of the mixture is 1.02 g/mL. Determine the Heat of Reaction ∆Hrxn for this process. – ∆Horeaction is “positive”: ENDOTHERMIC, ∴ ∆T is - (Tfinal < Tinitial ), Decrease temperature Instead of reaction, a specific amount of heat is added (or removed) in the calorimeter (example, when a hot metal bar or ice cubes is placed in a pail of water): (qcal + qwater) = - qinvolved For direct heat transfe...
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This document was uploaded on 03/26/2014.

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