I am studying Classical Mechanics in this semester, I want to know if there are any suggestions on some problem sets that will help me to master the skills needed.
In a free expansion, I know that we cannot use the equation dS=dQ/T...(1). Instead we use dS>dQ/T...(2).
The question is that why we can use △S=ncᵥln(T_f/T_i)+nRln(V_f/V_i) , which is derived from the equation(1), to calculate the entropy change? Shouldn’t it be a inequality too?
What are the major obstacles in the development of battery encountered currently? Or there are different difficulties in different aspects? I have tried to search it online but it's like searching for a needle in a haystack.