Reversible and Irreversible Processes — Prelims Questions

Which of the following conditions is NOT essential for a thermodynamic process to be reversible?

An ideal gas undergoes a free expansion. Which of the following statements is true regarding this process?

A system undergoes a reversible isothermal expansion from state 1 to state 2. The work done by the system is $W_{rev}$. If the same system undergoes an irreversible isothermal expansion from state 1 to state 2, what can be said about the work done, $W_{irr}$?

A heat engine operates between a hot reservoir at $T_H = 500\,\text{K}$ and a cold reservoir at $T_C = 300\,\text{K}$. If the engine is reversible, what is its efficiency? If a real engine operating between the same reservoirs has an efficiency of $30\%$, what can be inferred about its process?

Which of the following processes would result in an increase in the entropy of the universe?

A gas is compressed from $V_1$ to $V_2$. If the compression is done reversibly, the work done on the gas is $W_{rev}$. If the same compression is done irreversibly, the work done on the gas is $W_{irr}$. Which of the following relationships is correct?