Define an isothermal process and state two essential conditions for such a process to take place.

Answer

### Step-by-Step Solution

1. **Definition of Isothermal Process**:
An isothermal process is a thermodynamic process in which the temperature of the system remains constant throughout the entire process. This means that there is no change in temperature, and thus the change in internal energy of the system is zero for an ideal gas.

2. **Essential Condition 1 - Conducting Walls**:
For an isothermal process to occur, the walls of the system must be conducting. This allows for the transfer of heat between the system (the gas) and its surroundings. The conducting walls ensure that any heat added to or removed from the system can maintain the temperature at a constant level.

3. **Essential Condition 2 - Slow Compression or Expansion**:
The second essential condition is that the expansion or compression of the gas must occur very slowly. This slow process ensures that the system remains in thermal equilibrium with its surroundings, preventing any temperature difference from arising during the process.

### Summary of Conditions:
- **Condition 1**: The walls of the system must be conducting to allow heat exchange.
- **Condition 2**: The expansion or compression of the gas must be done slowly to maintain thermal equilibrium.