C401Ch17LN1 - Chapter 17: Thermodynamics Part 1 Spontaneity...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
Chapter 17: Thermodynamics Part 1 Spontaneity What does it mean when we say a process is spontaneous? A spontaneous process is one which occurs naturally with no external influence. The reverse process will not occur naturally under the same conditions! Spontaneous processes may occur slowly or quickly, spontaneous does not mean that it is an instantaneous process. What are some examples of spontaneous processes? Water running downhill (Ever see it go uphill naturally?) A ball rolling downhill Iron rusts in the presence of oxygen and water A gas fills an empty container (It would never evacuate the container on its own!) Wood burns to form carbon dioxide and water Hydrogen gas reacting with oxygen gas to form water (With a bang!) Water freezes below 0°C; water melts above 0°C (What does it do at 0°C?) • Cold packs • Hot packs So, how can you tell whether a chemical rxn or physical process will occur spontaneously (naturally with no external influence)? Also, why is a rxn spontaneous and under what conditions (temperature, etc.)? To answer this, we need to talk about the two factors of spontaneity: enthalpy (a measure of the heat energy change in a system) and entropy (a measure of the randomness or disorder of a system) Entropy Entropy, S, is a measure of the molecular disorder or randomness. Like enthalpy, entropy is a state function, so it is independent of path. ± S is the change in entropy of a system, ± S = S f – S i , and this value is also independent of path. You can see from the above equation, that if the entropy of a system increases, then ± S is positive, while it will be negative if the entropy decreases. It is true that chemical systems tend to move spontaneously in the direction which will increase the randomness or entropy of the system.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 06/25/2008 for the course CHEM 400-401 taught by Professor Dr.samples during the Fall '06 term at American River.

Page1 / 4

C401Ch17LN1 - Chapter 17: Thermodynamics Part 1 Spontaneity...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online