Mechanical Engineering - MCQ Practice Questions

Which of the following statements is correct regarding the first law of thermodynamics?

During an adiabatic expansion of an ideal gas, the temperature of the gas decreases. This is because:

What is the SI unit of entropy?

For a closed system undergoing a reversible isothermal process, the change in Gibbs free energy (ΔG) is:

A Rankine cycle (ideal steam cycle) is used in thermal power plants. Which process has the highest irreversibility?

If the specific heat at constant volume (Cv) for a diatomic ideal gas is 5R/2, what is its specific heat at constant pressure (Cp)?

During throttling of a real gas through an expansion valve, which thermodynamic property remains constant?

A system undergoes a cyclic process. The net work done by the system is 150 kJ and the net heat absorbed is 150 kJ. Which statement is correct?

In a turbocharger application, compressed air enters a turbine. If the isentropic efficiency of the turbine is 0.85, what does this indicate?

For an ideal gas in a constant pressure (isobaric) process from state 1 to state 2, the change in specific entropy is:

Which of the following processes has zero work done by/on the gas?

A heat pump operating between 280 K and 350 K has a coefficient of performance (COP) of 5. How much work input is required to transfer 1000 J of heat to the hot reservoir?

For a real gas undergoing Joule-Thomson expansion through a throttle valve, the Joule-Thomson coefficient (μ_JT) is negative. This means:

Steam at 80 kPa with enthalpy 2660 kJ/kg and entropy 7.31 kJ/kg·K. What is the thermodynamic state of this steam?

Which statement correctly describes the second law of thermodynamics?

In a diesel cycle, the expansion process (power stroke) is adiabatic. If the pressure and temperature at the end of compression are 40 bar and 850 K respectively, and the expansion ratio is 8, what is approximately the temperature at the end of expansion? (Take γ = 1.4)

A compressor compresses air from 1 bar and 25°C to 8 bar. If the isentropic efficiency is 0.80 and the process is adiabatic, what is the actual temperature of air after compression? (γ = 1.4, R = 287 J/kg·K)

For a substance, the triple point and critical point data are important in phase diagrams. At the triple point, how many phases can coexist?

A gas mixture contains N2 (40%) and O2 (60%) by mole fraction. What is the partial pressure of N2 if total pressure is 5 bar?

A reversible isothermal process occurs at 300 K for an ideal gas. If 5 kJ of heat is absorbed, what is the change in entropy of the system?