A 2 cm thick 10 cm tall candle is burning in a wellinsulated

A 2 cm thick, 10 cm tall candle is burning in a well-insulated room. It will take 100 hours for the candle to exhaust itself. Taking the room (the air plus the candle) as the system, determine the rate of heat transfer and the change in internal energy of the system during one hour of the burning process.

Solution

If you consider both candle and the air as the system, there will not be any heat transfer nor a change in the internal energy.

Firstly, the room is insulated, that is no heat can leave the room/system. So heat transfer is zero

And the internal energy also remains the same. Before the candle burns, the internal energy of the system is in the form of chemical energy of candle wax. After it is exhausted this internal energy gets converted to inter molecular energy of room air.

Whether it is 1 hour or 10 hours, the results are same