Final answer:
The energy conversions involved in burning coal to produce thermal energy are chemical energy → thermal energy → mechanical energy → electrical energy.
Step-by-step explanation:
The energy conversions that occur when coal is formed and then burned to produce thermal energy involve different forms of energy. Initially, the chemical energy contained in coal is converted into thermal energy as it burns to turn water into steam in a boiler. This thermal energy in the steam is then converted into mechanical energy as it spins a turbine, which is connected to a generator to produce electrical energy.
To summarize, the energy conversions involved in this process are: chemical energy in coal → thermal energy → mechanical energy → electrical energy.