Calorimetry Reviewer

CHEM 17 REVIEWER:

CALORIMETRY

Chemical Energy

* contributes to internal energy of a system

Heat of Reaction

* q exchanged when reaction occurs within system at CONSTANT TEMPERATURE

* Exothermic:

* ISOLATED SYSTEM: T INCREASE

NON-ISOLATED SYSTEM: T DECREASE

qrxn < 0

* Endothermic:

ISOLATED SYSTEM: T DECREASE

NON-ISOLATED SYSTEM: T INCREASE

qrxn > 0

Calorimetry

qrxn = -qcal

*qcal = qbomb + qwater + qwires . . .*

qcal = mc ΔT

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qcal = Ccal ΔT

* calibration – establishes a relation bet. quantity value and corresponding measurement

* Bomb Calorimeter

* Coffee-Cup Calorimeter

* system is isolated

* measure ΔT

* standardized using known reaction

1st Law of Thermodynamics

* U – total energy in system

* translational KE (molecule bond)

* molecular rotation (molecule rotates)

* bond vibration (vibrational bond)

* intermolecular attractions

* system contains only U

* heat and work only occur when there is change in system

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ΔU = q + w

Important Equations:

a. 1st Law of Thermodynamics

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qrxn = -qcal

b. Heat of reaction at constant pressure

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qrxn = nLR ΔHrxn

c. Calibration of Calorimeter

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Δ = - Ccal ΔTcal

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nLR

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Ccal = - (nLR * Δ )

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ΔTcal

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d. Determination of Enthalpy Change

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Δ = - [Ccal +( mx cx )] ΔT...