aula #07 · a comparison of dh and du dh 2na (s) + 2h 2 o (l) 2naoh (aq) + h2 (g) dh = -367.5...
TRANSCRIPT
Aula #07
Thermodynamics/Thermochemistry
Work ….
p as function of V …p ..constant…isobaric expansion
W1….W2….
- W2 > - W1dW = -pdV
e.g. p=RT/V
Thermodynamics &Thermochemistry
H ≡ U + pV (Defined as…)DU = q + w If dV=0… constant volume
dU = dq + dwDU = q
dH ≡ dU + d(pV)
DH = q
If dp=0… constant pressure dH ≡ dU + d(pV)
Work …. dW = -pdV
If dV=0… constant volume
If dp=0… constant pressureDH = q
DU = qWork ….
dW = -pdV
Thermodynamics/Thermochemistry dU = dq + dw
W2….
A Comparison of DH and DU
2Na (s) + 2H2O (l) 2NaOH (aq) + H2 (g) DH = -367.5 kJ/molDH
DU
DH = DU + pDV
P = 1 bar, T = 25 ºC
Dn(g) = 1 mol
DH = q
Thermodynamics &Thermochemistry
A Comparison of DH and DU
2Na (s) + 2H2O (l) 2NaOH (aq) + H2 (g) DH = -367.5 kJ/molDH
DU DH = DU + pDV
DU = DH - pDV
DU ≡ DH - Dn(g) RT = -367.5 - 2.5 = -370.0 kJ/mol
(pDV = Dn(g)RT)
P = 1 bar, T = 25 ºC
Dn(g) = 1 mol
Thermodynamics &Thermochemistry
dW = -pdV
Thermochemistry
Constant-Pressure CalorimetryNo heat enters or leaves!
qsys = qwater + qcal + qrxn
qrxn = - (qwater + qcal)
qwater = m x c x Dt qcal = Ccal xDt
Reaction occurs at Fixed P DH = qrxn
qsys = 0
Thermochemistry
Constant-Volume Calorimetry
qsys = qwater + qbomb + qrxn
qsys = 0
qrxn = - (qwater + qbomb)
qwater = m x c x Dt
qbomb = Cbomb xDt
Reaction at Constant V DU = qrxn
Atomization
Thermodynamics &Thermochemistry
e.g. The Solution Process for NaCl
DHsoln = Step 1 + Step 2 = 788 – 784 = 4 kJ/mol
Thermodynamics &Thermochemistry
Acetone
e.g. The Solution Process for NaCl
NaCl
Thermodynamics &Thermochemistry
water
Thermodynamics &Thermochemistry
Acetone
e.g. The Solution Process for NaCl
NaCl
Thermodynamics &Thermochemistry
water