Question 3.2: For liquid acetone at 20°C and 1 bar, β = 1.487 × 10^−3 °C^...
For liquid acetone at 20°C and 1 bar,
β = 1.487 \times 10^{−3 }° C^{−1} κ = 62 \times 10^{−6} bar^{ −1} V = 1.287 cm^{3} ⋅g^{−1}
For acetone, find:
(a) The value of (∂ P / ∂ T) V at 20°C and 1 bar.
(b) The pressure after heating at constant V from 20°C and 1 bar to 30°C.
(c) The volume change when T and P go from 20°C and 1 bar to 0°C and 10 bar.
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(a) The derivative ( ∂ P / ∂ T )_{V} is determined by application of Eq. (3.5) to the case for which V is constant and dV = 0:
\frac{dV}{V} =\beta dT – k dP (3.5)
β dT − κ dP = 0 ( const V )
or
\left(\frac{∂ P}{∂ T} \right) _{V} = \frac{\beta }{K} = \frac{1.487 \times 10^{-3} }{62 \times 10^{-6} }= 24 bar ⋅ °C^{-1}
(b) If β and κ are assumed constant in the 10°C temperature interval, then for constant volume Eq. (3.6) can be written:
\frac{V_{2} }{V_{1} }= \beta (T_{2} – T_{1} ) – k (P_{2 } – P_{1} ) (3.6)
p_{2} = p_{1} + \frac{\beta }{k} \left(T_{2} – T_{1} \right) = 1 bar + 24 bar . °C^{−1} × 10°C = 241 bar
(c) Direct substitution into Eq. (3.6) gives:
In \frac{V_{2} }{V_{1} } = ( 1.487 \times 10^{−3} ) ( −20 ) − ( 62 \times 10^{−6} ) ( 9 ) = −0.0303
\frac{V_{2} }{V_{1} } = 0.9702 and V_{2} = ( 0.9702 ) ( 1.287 ) = 1.249 cm^{ 3}⋅g^{−1}
Then,
ΔV = V_{2} – V_{1} = 1.249 − 1.287 = −0.038 cm^{ 3} ⋅g^{ −1}