Adiabatic Process and Density Change

The question asks about a specific type of thermodynamic process for a gas where there is a change in density but no heat is exchanged with the surroundings. We need to identify which standard thermodynamic process fits this description.

Heat Exchange Condition

The key condition mentioned is "no heat exchange to and from the gas". In thermodynamics, heat exchange is represented by the symbol $\Delta Q$. So, this condition means $\Delta Q = 0$.

Understanding the Options

Let's look at the given options and their definitions:

• Exothermal process: This is a process that releases heat into the surroundings. This directly contradicts the condition of no heat exchange.
• Adiabatic process: This is a thermodynamic process that occurs without transfer of heat or mass of substance between a thermodynamic system and its surroundings. The condition for an adiabatic process is $\Delta Q = 0$. This matches the condition given in the question.
• Isothermal process: This is a process during which the temperature of a system remains constant ($\Delta T = 0$). While temperature is constant, heat exchange ($\Delta Q$) typically occurs to maintain this constant temperature, especially if work is done. This does not fit the condition of no heat exchange.
• Internal process: This is not a standard term for a specific thermodynamic process type defined by heat or temperature conditions.

Density Change in an Adiabatic Process

The question also mentions a "change in density". Density ($\rho$) is defined as mass ($m$) per unit volume ($V$), i.e., $\rho = \frac{m}{V}$. For a fixed amount of gas (constant mass $m$), a change in density means there must be a change in volume $V$.

In an adiabatic process, even though there is no heat exchange ($\Delta Q = 0$), work ($W$) can be done by or on the gas. According to the first law of thermodynamics, $\Delta U = \Delta Q - W$, where $\Delta U$ is the change in internal energy. If $\Delta Q = 0$, then $\Delta U = -W$.

Work done on the gas (compression) decreases its volume and increases its internal energy (and temperature for an ideal gas). A decrease in volume leads to an increase in density ($\rho = m/V$).

Work done by the gas (expansion) increases its volume and decreases its internal energy (and temperature for an ideal gas). An increase in volume leads to a decrease in density.

Therefore, a change in volume, and consequently a change in density, can certainly occur during an adiabatic process.

Conclusion

The process characterized by no heat exchange ($\Delta Q = 0$) while allowing for changes in volume (and thus density) and temperature is called an adiabatic process.

Based on the analysis, the process described is the adiabatic process.