Chapter 3

# Coolingslowlythevapor

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Unformatted text preview: calculate the entropy change ΔS = SB ‐ SA for an irreversible process  between A and B, one cannot integrate δq / T, the ratio of the heat  increment over the temperature, along the actual path followed during the  A‐B process, since dS = δq / T only applies to reversible processes. Indeed,  the second law states that: dS &gt; δ q / T for an irreversible process.  However, since the entropy is a state function, the entropy change ΔS does  not depend on the path chosen. Since we know how to calculate entropy  change for the system along any reversible path, we will imagine a  hypothetical path between A and B that is reversible.  We will now  consider some examples to illustrate this concept.    Example 1:   Two blocks of metal A, and B, of masses mA and mB, initially at  temperatures TA and TB are placed in contact with one another in a  thermally insulated container.  As a result of the difference in their initial  temperatures and of the fact that they are placed in contact with each  other, they will exchange heat with each other until they exhibit the same  final temperature, TF.  Heat is exchanged only between the two blocks since  Marand’s Notes: Chapter 3 ‐ The Second Law of Thermodynamics  102  they are placed in a thermally insulated container (adiabatic process).  Considering the two blocks to form the System, no heat is exchanged  between system and surroundings.  Therefore: q = qA‐B + qB‐A = 0   where qA‐B is the heat received by A from B (qA...
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## This note was uploaded on 01/26/2014 for the course CHEM 3615 taught by Professor Aresker during the Spring '07 term at Virginia Tech.

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