Chapter 06: Thermochemistry Flashcards Preview

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Flashcards in Chapter 06: Thermochemistry Deck (35)
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31

Bomb calorimeter

Constant-volume calorimetry

Since volume is constant, no work is done, w = 0

Thus:

ΔErxn = qv = qrxn

-qrxn = qcal = Ccal × ΔT

qcal is heat absorbed by calorimeter
-qrxn is heat released by reaction
Ccal is heat capacity of calorimeter

32

Coffee-cup calorimetry

Constant-pressure calorimetry

Used to measure enthalpy of a reaction: ΔHrxn

qsoln = msoln × Cs, soln × ΔT

and

qrxn = -qsoln = qp =  ΔHrxn

33

Standard enthalpy of formation

ΔHf°

The heat change that results when one mole of a compound is formed from its elements at a pressure of 1 atm

ΔHf° of any element in most stable form is zero

stable liquids: Hg, Br

stable gases: H2, N2, O2, F2, Cl2, noble gases

note: C graphite is stable, not C diamond, though

note: S8 rhombic is stable

34

Standard enthalpy of a reaction

ΔHrxn°

The enthalpy of a reaction carried out at 1 atm

ΔHrxn° = ΣnproductsΔHf° - ΣnreactantsΔHf°

n = number of moles

35

Hess' law

When reactants are converted to products, the change in enthalpy is the same whether the reaction takes place in one step or a series of steps

ΔHrxn° = ΔH1° + ΔH2°