All we know that heat is transferred from high temperature region to low temperature region always. And this process is also the spontaneous process.
The second law of thermodynamics is based on the heat energy and work energy transfer and which is stated as follows.
Statement:
According to second law of thermodynamics, heat cannot be totally converted into work untill there will be no permanent changes produced in the system or in the surrounding.
Explanation:
- Let us consider a heat engine which continuously converts heat energy into work energy. The heat engine may take heat energy from the high temperature region and converts it into work but some amount heat energy will be remained and it is given to the sink which is at lower temperature. And efficiency of engine is the ratio of work done to the total heat absorbed.
- The efficiency of heat engine will be unity only when total heat energy absorbed will be converted into work totally.
- And hence we can say that, there is no machine is developed which is having 100% efficiency.
- And this is another statement of the second law of the thermodynamics.
Applications:
- The second law of thermodynamics proved that the heat is always transferred from high temperature region to the lower temperature region only.
- The second law of thermodynamics is applicable in all types of heat engines.
- Also, in case of plants, during the process of photosynthesis the total heat or light energy absorbed is not used to form the food but some of it get reflected and some of get evolved in the surrounding. So, this is also the second law of thermodynamics.