If gas in a cylinder is maintained at a constant temperature T, the pressure P is related to the volume by a formula of the form
\(P=\frac{nRT}{V-nb}-\frac{an^2}{V^2}\)
(a) in which a, b, n, and R are constants. Find dP/dV.
(b) Now suppose temperature is not constant and that T, P, and V are functions of time t. Find dP/dt.
(c) Describe in words the meanings of dP/dV and dP/dt.

Respuesta :

Answer:

(a)  [tex]\frac{dP}{dV}=\frac{2an^2}{V^3}-\frac{nRT}{(V-nb)^2}[/tex]

(b) [tex]\frac{dP}{dt}=\frac{nR(V-nb)\frac{dT}{dt}-nRT\frac{dV}{dt}}{(V-nb)^2}+\frac{2an^2\frac{dV}{dt}}{V^3}[/tex]

(c) [tex]\frac{dP}{dV}[/tex] is the rate change of pressure of the gas per unit volume.

[tex]\frac{dP}{dt}[/tex] is the rate change of pressure of the gas per unit time.

Step-by-step explanation:

Formula:

  • [tex]\frac{d}{dx}(\frac uv)=\frac {v\frac{d}{dx}v-u\frac{d}{dx}v}{v^2}[/tex]

Given that,

[tex]P=\frac{nRT}{V-nb}-\frac{an^2}{V^2}[/tex]

(a)

[tex]P=\frac{nRT}{V-nb}-\frac{an^2}{V^2}[/tex]

Differentiating with respect to V

[tex]\frac{dP}{dV}=\frac{(V-nb)\frac{d}{dV}(nRT)-(nRT)\frac{d}{dV}(V-nb)}{(V-nb)^2}-\frac{V^2\frac{d}{dV}(an^2)-(an^2)\frac{d}{dV}V^2}{(V^2)^2}[/tex]

      [tex]=\frac {-nRT}{(V-nb)^2}-\frac{-an^2. 2V}{V^4}[/tex]

     [tex]=\frac{2an^2}{V^3}-\frac{nRT}{(V-nb)^2}[/tex]

(b)

[tex]P=\frac{nRT}{V-nb}-\frac{an^2}{V^2}[/tex]

Differentiating with respect to t

[tex]\frac{dP}{dt}=\frac{(V-nb)\frac{d}{dt}(nRT)-(nRT)\frac{d}{dt}(V-nb)}{(V-nb)^2}-\frac{V^2\frac{d}{dt}(an^2)-(an^2)\frac{d}{dt}V^2}{(V^2)^2}[/tex]

    [tex]=\frac{(V-nb)nR\frac{dT}{dt}-nRT\frac{dV}{dt}}{(V-nb)^2}-\frac{-an^2.2V\frac{dV}{dt}}{V^4}[/tex]

    [tex]=\frac{nR(V-nb)\frac{dT}{dt}-nRT\frac{dV}{dt}}{(V-nb)^2}+\frac{2an^2\frac{dV}{dt}}{V^3}[/tex]

(c)

[tex]\frac{dP}{dV}[/tex] is the rate change of pressure of the gas per unit volume.

[tex]\frac{dP}{dt}[/tex] is the rate change of pressure of the gas per unit time.