# Quantification of Entropy and the 2nd Law of Thermodynamics

• transmini

#### transmini

All of my information comes from my current chemistry class, I just want to know where I either may have misread, misinterpreted, or was mistold information.

With the 2nd Law of Thermodynamics we can say $$\space\space \Delta{S}_{universe} = \Delta{S}_{surroundings} + \Delta{S}_{system} > 0$$
Then using $$\space\space \Delta{S}_{system} = \frac{q_{rev}}{T}$$
with (at constant pressure) $$\space\space q = \Delta{H}$$
and (from the 1st Law of Thermodynamics) $$\space\space \Delta{H}_{system} + \Delta{H}_{surroundings} = 0$$
we can get $$\space\space \Delta{S}_{system} = \frac{\Delta{H}_{system}}{T}$$ $$\space\space \Delta{S}_{surroundings} = \frac{\Delta{H}_{surroundings}}{T} = \frac{-\Delta{H}_{system}}{T}$$.
Substituting these back into  would give $$ \space\space \Delta{S}_{universe} = \frac{-\Delta{H}_{system}}{T} + \frac{\Delta{H}_{system}}{T} > 0$$
which simplifies to $$0 > 0$$
which is not true.

I'm assuming I did something wrong with this, but cannot figure out what. Where is the issue?

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