My doubts about the law of conservation of energy?

The total amount of energy is constant, but the transformation of energy is directional.

1, for example, when coal is burned, chemical energy is converted into heat energy. But it can't spontaneously convert thermal energy into chemical energy in coal.

2. Let me give you another example: electric light converts electric energy into light energy and heat energy-light energy will also become heat energy after repeated reflection and absorption. Once the electricity is used up, if the non-ideal situation is not considered, the indoor temperature should be measured to rise a little. However, the temperature in the room can't drop a little spontaneously, so you can turn on the electricity again.

-

So energy is conserved. However, the "available" energy is limited, so human beings will face energy problems.

-

There is also the second law of thermodynamics about the direction of energy conversion. From this, it can be concluded that the destination of the universe is a state with the largest entropy-the so-called "theory of heat death". You can learn about it if you are interested.