Boyle’s Law states that when a sample of gas is compressed at a constant temperature, the pressure P of the gas is inversely proportional to the volume V of the gas. (a) Suppose that the pressure of a sample of air that occupies 0.106 m3 at 25°C is 50 kPa. Write V as a function of P. (b) Calculate dVydP when P − 50 kPa. What is the meaning of the derivative? What are its units?

Respuesta :

Answer:

a)[tex]V=\dfrac{5.3}{P}[/tex]

b)[tex]ML^{-4}T^{-2}[/tex].

Explanation:

Given that

Boyle's law

P V = Constant ,at constant temperature

a)

Given that

[tex]P_1=50KPa[/tex]

[tex]V_1=0.106m^3[/tex]

We know that for PV=C

[tex]P_1V_1=P_2V_2=PV[/tex]

Now by putting the values

PV= 50 x 0.106

[tex]V=\dfrac{5.3}{P}[/tex]

Where P is in KPa and V is in [tex]m^3[/tex]

b)

PV= C

Take ln both sides

So [tex]\ln(PV)=\ln C[/tex]

lnP + lnV =lnC               ( C is constant)

By differentiating

[tex]\dfrac{dP}{P}+\dfrac{dV}{V}=0[/tex]

So

[tex]\dfrac{dP}{dV}=-\dfrac{P}{V}[/tex]

When P= 50 KPa

[tex]\dfrac{dP}{dV}=-\dfrac{50}{V}\ \dfrac{KPa}{m^3}[/tex]

It indicates the slope of PV=C curve.

It unit is [tex]\dfrac{Pa}{m^3}[/tex].

Or we can say that [tex]ML^{-4}T^{-2}[/tex].

Answer:

(a) V = [tex]\frac{8.3}{P}[/tex]

(b) (i) the value of [tex]\frac{dV}{dP}[/tex] when P = 50kPa is - 0.00332 [tex]\frac{m^{3} }{kPa}[/tex]

(ii) the meaning of the derivative [tex]\frac{dV}{dP}[/tex] is the rate of change of volume with pressure.

(iii) and the units are [tex]\frac{m^{3} }{kPa}[/tex]

Explanation:

Boyle's law states that at constant temperature;

P ∝ 1 / V

=> P = k / V

=> PV = k   -------------------------(i)

Where;

P = pressure

V = volume

k = constant of proportionality

According to the question;

When;

V = 0.106m³, P = 50kPa

Substitute these values into equation (i) as follows;

50 x 0.106 = k

Solve for k;

k = 5.3 kPa m³

(a) To write V as a function of P, substitute the value of k into equation (i) as follows;

PV = k

PV = 8.3

Make V subject of the formula in the above equation as follows;

V = 8.3/P

=> V = [tex]\frac{8.3}{P}[/tex]        -------------------(ii)

(b) Find the derivative of equation (ii)  with respect to V to get dV/dP as follows;

V = [tex]\frac{8.3}{P}[/tex]

V = 8.3P⁻¹

[tex]\frac{dV}{dP}[/tex] = -8.3P⁻²

[tex]\frac{dV}{dP}[/tex] = [tex]\frac{-8.3}{P^{2} }[/tex]

Now substitute P = 50kPa into the equation as follows;

[tex]\frac{dV}{dP}[/tex] = [tex]\frac{-8.3}{50^{2} }[/tex]   [[tex]\frac{kPam^{3} }{(kPa)^{2} }[/tex]]               -----  Write and evaluate the units alongside

[tex]\frac{dV}{dP}[/tex] = [tex]\frac{-8.3}{2500 }[/tex]    [[tex]\frac{kPam^{3} }{k^{2} Pa^{2} }[/tex]]

[tex]\frac{dV}{dP}[/tex] = - 0.00332 [[tex]\frac{m^{3} }{kPa}[/tex]]

Therefore,

(i) the value of [tex]\frac{dV}{dP}[/tex] when P = 50kPa is - 0.00332 [tex]\frac{m^{3} }{kPa}[/tex]

(ii) the meaning of the derivative [tex]\frac{dV}{dP}[/tex] is the rate of change of volume with pressure.

(iii) and the units are [tex]\frac{m^{3} }{kPa}[/tex]