Unit 9: Topic 1 - Introduction to Entropy Flashcards
What is entropy?
Entropy is a measure of the molecular disorder of a system. To be more specific, it is a measure of a system’s thermal energy unavailable to do work per unit temperature.
Does entropy increase or decrease in phase changes from solid to liquid and liquid to gas?
For phase changes from solid to liquid and liquid to gas, entropy increases. This is due to the differences between the movement of molecules in solids, liquids, and gases. Molecules in a solid are confined to only some vibration and are held in place by intermolecular bonds. In a liquid, molecules are free to move by sliding over one another. Gas molecules can freely disperse away from one another. As freedom of movement increases, entropy also increases.
Does entropy increase or decrease in phase changes from gas to liquid and liquid to solid?
For phase changes from gas to liquid and liquid to solid, entropy decreases. This is because the particles become more confined and result in less disorder.
For a gas at constant temperature, does entropy increase or decrease when the volume increases?
As entropy is a measure of molecular disorder, it can also be described as the number of possible molecular configurations of a system (microstates). When volume increases, the gas molecules will disperse to fill up that additional volume. As a result, there are more possible locations for each gas molecule to be in, which increases the number of microstates and thus entropy as well.
When does entropy increase for reactions involving gas-phase reactants or products? When does entropy decrease?
When there are more moles of gas-phase products than gas-phase reactants, entropy increases. Similarly, when there are more moles of gas-phase reactants than gas-phase products, entropy decreases.
Does entropy increase or decrease in the reaction CaCO3(s) –> CaO(s) + CO2(g)?
Entropy increases in the reaction because the reactants have 0 moles of gas, whereas the products have 1 mole of gas.
Why does entropy increase with temperature?
When temperature increases, particles have greater kinetic energy and thus move faster. This creates more disorder and, as a result, increases entropy.
