Isothermal reaction or isothermal process is when the temperature during the time reaction takes place or during the time process takes place the temperature of the system is held at the same temperature.
There is a possibility of an exchange of heat from the environment to the system in isothermal process. The heat energy supplied to the system or the heat energy released from the system is shared with the environment and surroundings, with the temperature of system being held same.
In an adiabatic change, there is no exchange of heat energy between the environment and the system. Hence, all the heat supplied to the system remains within the system and hence, increases the internal energy of the system. The energy supplied will be changing the temperature of the system.