Jack asked in Science & MathematicsPhysics · 7 years ago

n = 2.75 mol of Hydrogen gas is initially at T = 324 K temperature and pi = 2.20×105 Pa pressure. The gas is t?

n = 2.75 mol of Hydrogen gas is initially at T = 324 K temperature and pi = 2.20×105 Pa pressure. The gas is then reversibly and isothermally compressed until its pressure reaches pf = 6.76×105 Pa. What is the volume of the gas at the end of the compression process?

How much work did the external force perform?

How much heat did the gas emit?

How much entropy did the gas emit?

What would be the temperature of the gas, if the gas was allowed to adiabatically expand back to its original pressure?

Totally confused, any help would be awesome

2 Answers

Relevance
  • Mohasa
    Lv 4
    7 years ago
    Favorite Answer

    For an isothermal process

    PV = nRT = constant

    So PiVi = nRTi = PfVf

    Vf = nRTi/Pf

    n = 2.75 moles

    R = 8.31 J/(mol.°K)

    Ti = 324 °K

    Pf = 6.76 x 10^5 Pa

    Vf = 2.75*8.31*324 / (2.20 * 10^5) m^3

    Vf = 3.366 x 10^(-2) m^3 <===

    For an isothermal process, the work is

    W = nRT ln(Vi/Vf)

    Since PiVi = PfVf, we have Vi/Vf = Pf/Pi and

    W = 2.75*8.31*324 ln(6.76 * 10^5/ (2.20*10^5)) J

    W = 8311.7 J <===

    ΔE = Q + W

    For an isothermal process, the change in internal energy is zero : ΔE = 0

    Thus Q = - W = - 8311.7 J is the heat emitted <===

    ΔS = nCv ln(Tf/Ti) + nR ln(Vf/Vi) for the entropy change of an ideal gas

    For an isothermal process, Tf = Ti and

    ΔS = nR ln(Vf/Vi)

    From PiVi = PfVf, we have Vf/Vi = Pi/Pf so

    ΔS = nR ln(Pi/Pf) = 2.75*8.31 ln(2.20 * 10^5/ (6.76*10^5)) J/°K

    ΔS = -25.65 J/°K <=== is the change of entropy

    For an adiabatic process, PV^γ = constant where γ = 1.384 for hydrogen

    So P1/P2 = (V2/V1)^γ....(i)

    Note: V1, P1 are the initial values and V2, P2 the final values of the volume

    and pressure in this question.

    We use the gas law PV = nRT to replace V2/V1

    P1V1 = nRT1 and P2V2 = nRT2 which gives

    V2/V1 = (nRT2/P2)/(nRT1/P1)

    or V2/V1 = P1 T2/ (P2 T1). Substitute this in eqn (i)

    P1/P2 = (P1 T2/ (P2 T1))^γ

    P1/P2 = (P1/P2)^γ (T2/T1)^γ

    So (P1/P2)^(1-γ) = (T2/T1)^γ

    γ ln(T2/T1) = (1-γ) ln(P1/P2)

    lnT2 - lnT1 = (1-γ)/γ * ln(P1/P2)

    lnT2 = lnT1 + (1-γ)/γ * ln(P1/P2)

    T1 = 324 °K

    γ = 1.384 for hydrogen

    P1 = 6.76 x 10^5 Pa

    P2 = 2.20 x 10^5 Pa so

    lnT2 = ln324 + (1-1.384)/1.384 ln(6.76 * 10^5/ (2.20*10^5))

    lnT2 = 5.7807 - 0.3115

    T2 = 237.3 °K <=== is the final temperature

    Hope this helps

    • Login to reply the answers
  • Anonymous
    3 years ago

    the main serious techniques that the folk can try against worldwide warming is getting rid of their older form vehicles (1979 Buick) because of the fact, older vehicles emmitt extra poisonous fumes into the air. Its obtrusive that the extra technological stepped forward a vehicle is, the fewer risky gases it emmitts. A vehicle that become outfitted 3 or 4 years in the past would be extra financial device friendly than a vehicle that become assembled 35 years in the past. for best populated cities at the same time with long island, Bus and Taxi companys ought to replace present day vehicles with vehicles that are powered by skill of hydrogen or electricity. purely think of, if each and every significant city used the Toyota Prius as taxi's, there could be a decreased point of pollution, and additionally taxi fares would desire to be notably decrease as nicely.

    • Login to reply the answers
Still have questions? Get your answers by asking now.