Molecular Physics | Thermodynamics Answers

A system consisting of 1 kg of an ideal gas at 5 bar pressure and 0.02 m3

volume executes a cyclic process comprising the following three distinct operations : (i) Reversible

expansion to 0.08 m3 volume, 1.5 bar pressure, presuming pressure to be a linear function of

volume (p = a + bV), (ii) Reversible cooling at constant pressure and (iii) Reversible hyperbolic

compression according to law pV = constant. This brings the gas back to initial conditions.

(i) Sketch the cycle on p-V diagram.

(ii) Calculate the work done in each process starting whether it is done on or by the system

and evaluate the net cyclic work and heat transfer.

a cylinder of 8 cm inside diameter having a piston loaded

with a spring (stiffness = 150 N/cm of compression). The initial pressure, volume and tempera￾ture of air in the cylinder are 3 × 105 N/m2, 0.000045 m3 and 20°C respectively. Determine the

amount of heat added to the system so that piston moves by 3.5 cm.

Assume cv = 0.71 kJ/kg K and R = 0.287 kJ/kg K.

10 kg of fluid per minute goes through a reversible steady flow process. The

properties of fluid at the inlet are : p1 = 1.5 bar, ρ1 = 26 kg/m3, C1 = 110 m/s and u1 = 910 kJ/kg and

at the exit are p2 = 5.5 bar, ρ2 = 5.5 kg/m3, C2 = 190 m/s and u2 = 710 kJ/kg. During the passage,

the fluid rejects 55 kJ/s and rises through 55 metres. Determine :

(i) The change in enthalpy (∆ h) ;

(ii) Work done during the process (W).

. 0.15 m3 of an ideal gas at a pressure of 15 bar and 550 K is expanded

isothermally to 4 times the initial volume. It is then cooled to 290 K at constant volume and then

compressed back polytropically to its initial state.

Calculate the net work done and heat transferred during the cycle.

1. 0.1 m3 of an ideal gas at 300 K and 1 bar is compressed adiabatically to 8

bar. It is then cooled at constant volume and further expanded isothermally so as to reach the

condition from where it started. Calculate :

(i) Pressure at the end of constant volume cooling.

(ii) Change in internal energy during constant volume process.

(iii) Net work done and heat transferred during the cycle. Assume

cp = 14.3 kJ/kg K and cv = 10.2 kJ/kg K.

Nitrogen is contained in a 80-L tank and the initial pressure and temperature is 250 kPa and 200 ⁰C, respectively.

Determine:

a. the mass of the gas in kg.

b. Now, if 0.05 kg of gas leaks out of the tank and in the process the temperature drops to 33 ^oC. Find the gage pressure of the gas remaining in the tank in kPa, if the atmospheric is 100 kPa.

a. m = _____ kg Answer in 3 decimal places

b. P = _____ kPag

For a certain ideal gas R = 25.8 ft-lb_f/lb_m-⁰R and k = 1.09 (a) What are the values of c_p and c_v? (b) What mass of this gas would occupy a volume of 15 cu ft at 75 psia and 80⁰F? (c) If 30   Btu are transferred to this gas at constant volume in (b), what are the resulting temperature and pressure?

a. C_p = ____ Answer in 4 decimal places

C_v = _____ Answer in 4 decimal places

b. m = ______ lb Answer in 2 decimal places

c. T₂ = _____

P₂ = ______ psia

An ideal gas at 0.80 atmospheres and 87°C occupies 0.450 liter. How many moles are in the sample? (R = 0.0821 liter-atm/mole – K)

n = ____ mol

An insulated box containing helium gas falls from a balloon 4.5 km above the earth’s surface. Calculate the temperature rise in ^oC of the helium when box hits the ground.

Temperature rise = ____ ^oC