Absolute Entropy and Entropy Change
Sophie Anderson
7 min read
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Study Guide Overview
This study guide covers entropy and spontaneity, focusing on absolute entropy (S°) and change in entropy (ΔS°). It explains how to calculate ΔS° using standard entropy values and predict its sign based on phase changes, number of moles, and molecular complexity. The guide also includes practice problems and emphasizes the concept of state functions. Key exam topics and tips for predicting and calculating entropy changes are provided.
#Thermodynamics: Entropy and Spontaneity
Hey there, future AP Chem master! Let's dive into entropy, a concept that's all about disorder and spontaneity. This guide will help you nail those tricky questions on the exam. Let's get started!
#Entropy (S) - The Measure of Disorder
#Absolute Entropy (S°) vs. Change in Entropy (ΔS°)
- Entropy (S) is a measure of the disorder or randomness of a system. Think of it as how many ways a system can be arranged.
Absolute Entropy (S°): This is the entropy of a substance at standard conditions (1 atm and 273 K). It's a measure of the number of possible states a molecule can take. You'll usually find these values in tables (like the one below) and you'll be given these values on the exam.
Caption: A table showing standard entropies (S°) for various substances. Note that these values are always positive, unlike ΔH° values.
#State Functions: Pathway Independence
- A state function is a property that depends only on the current state of the system, not on how it got there. It's pathway-independent.
- Examples of state functions: Altitude change when climbing a mountain, enthalpy (H), and, you guessed it, entropy (S).
- Non-state function example: Distance traveled. The distance you travel depends on the path you take.
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