Consider a mixture of air and gasoline vapor in a cylinder with a piston. The original volume is 40. cm3. If the combustion of this mixture releases 950. J of energy, to what volume will the gases expand against a constant pressure of 650. torr if all the energy of combustion is converted into work to push back the piston

Respuesta :

Answer:

The volume needed to expand the gas is = 11 Lit = 11000 [tex]cm^{3}[/tex]

Explanation:

Given :

Initial volume [tex]V_{1} = 40 cm^{3} = 0.04[/tex] Lit.

Energy [tex]W = 950[/tex] J = 9.38 Lit × atm.   ⇒ ( 1 Lit×atm. = 101.325 J )

Pressure [tex]P =[/tex] 650 torr = 0.855 atm. ⇒ ( 1 torr = 0.00132 atm )

In this example we have to be aware of unit conversion system.

From the laws of thermodynamics,

 [tex]W = P \Delta V[/tex]  

Here in this example, all the energy of combustion is converted into work to push back the piston

[tex]W = P (V_{2} - V_{1} )[/tex]

[tex]V_{2} - 0.04 = 10.96[/tex]

[tex]V_{2} = 11[/tex] Lit = [tex]11000 cm^{3}[/tex]

The given system is a constant pressure system where the work done is the product of the pressure and the volume change.

  • The volume to which the gas expands to is approximately 11 liters

Reasons:

Given parameters;

The original volume, V₁ = 40 cm³

The energy released, E = 950 J

Constant pressure applied, P = 650 torr.

Condition: All energy is converted to work to push back the piston

Required:

The volume to which the gas will expand

Solution;

The work done, W = Energy releases, E = 950 J

Work done at constant pressure, W = P·(V₂ - V₁)

Where;

V₂ - The volume to which the gas will expand

Converting the volume to from cm³ to m³ gives;

V₁ = 40 cm³ = 0.00004 m³

Converting the pressure given in torr to Pascals gives;

650 torr. = 86659.54 Pa.

Therefore, we get;

950 J = 86659.54 Pa. × (V₂ - 0.00004 m³)

[tex]V_2 = \dfrac{950 \, J}{86659.54 \, Pa} + 0.00004 \, m^3 = \dfrac{2888}{263445} \ m^3 + 0.00004 \, m^3 = \dfrac{2683}{243855} \, m^3[/tex]

Converting to liters gives;

[tex]V_2 =\dfrac{2683}{243855} \, m^3 \times \dfrac{1,000 \, l }{m^3} \approx 11.00244\, l \approx 11 \, l[/tex]

  • The volume to which the gas expands, V₂ ≈ 11 liters.

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