Which out of the following can be determined ? Absolute internal energy, absolute enthalpy, absolute entropy.
Answers
Can we measure the absolute entropy and internal energy or enthalpy? Why?
We can measure the absolute entropy of a substance because of the existence of the third law of thermodynamics. It basically says that the entropy of a perfect crystal at absolute zero is 0. With your lower reference point as 0, you can be assured that any entropy you measure above that will be its absolute. Let’s say you have a ruler marked from x to y and 0 to y. When you measure with the former, you can only get a relative sense because the lower bound cannot be determined. We know that from x, it is y length long but what we do not know is the value of x. However, in the second case, you can get an absolute sense as the lower bound is well defined as 0.
We cannot measure absolute enthalpy or internal energy for the same reason as stated above. There is no lower reference point we can take with absolution, so we have to develop a relative scale.