Introduction to entropy  Applications of thermodynamics  AP Chemistry  Khan Academy  Summary and Q&A
TL;DR
Entropy is related to the number of microstates in a system, representing the possible arrangements and energies of particles. Increasing the number of microstates increases entropy, while decreasing it decreases entropy.
Questions & Answers
Q: What is entropy and how is it related to microstates?
Entropy is a measure of the number of microstates in a system, representing the possible arrangements and energies of particles. An increase in microstates leads to an increase in entropy, while a decrease leads to a decrease in entropy.
Q: How do changes in volume affect the number of microstates and entropy?
Increasing the volume of a system increases the number of possible positions for the particles, resulting in an increase in the number of microstates and entropy. Conversely, decreasing the volume decreases the number of microstates and entropy.
Q: How does increasing temperature affect the number of microstates and entropy?
Increasing the temperature of a system increases the average speed and range of velocities of the particles. This leads to more possible speeds and kinetic energies, increasing the number of microstates and entropy.
Q: How does the number of moles of gas particles affect entropy?
Increasing the number of moles increases the number of possible arrangements and distributions of particles, leading to an increase in the number of microstates and entropy.
Summary & Key Takeaways

Entropy is a measure of the number of microstates in a system, representing the possible positions and energies of particles.

An increase in the number of microstates leads to an increase in entropy, while a decrease in the number of microstates leads to a decrease in entropy.

Changes in volume, temperature, number of moles, and intermolecular forces can all affect the number of microstates and, therefore, the entropy of a system.