If you like us, please share us on social media, tell your friends, tell your professor or consider building or adopting a Wikitext for your course.

GeoWiki.png
ChemWiki: The Dynamic Chemistry Hypertext > Core > Physical Chemistry > Thermodynamics > State Functions > Internal Energy

Internal Energy

The internal energy of a system is identified with the random, disordered motion of molecules; the total (internal) energy in a system includes potential and kinetic energy. This is contrast to external energy which is a function of the sample with respect to the outside environment (e.g. kinetic energy if the sample is moving or potential energy if the sample is at a height from the ground etc). The symbol for Internal Energy Change is\( ΔU\).

Energy on a smaller scale

  • Internal energy includes energy on a microscopic scale
  • It is the sum of all the microscopic energies such as:
    1. translational kinetic energy
    2. vibrational and rotational kinetic energy
    3. potential energy from intermolecular forces

 

Example

One gram of water at zero °Celsius compared with one gram of copper at zero °Celsius do NOT have the same internal energy because even though their kinetic energies are equal, water has a much higher potential energy causing its internal energy to be much greater than the copper's internal energy.

Internal Energy Change Equations

The first law of thermodynamics

ΔU = q+w

where q is heat and w is work

An isolated system cannot exchange heat or work with its surroundings making the change in internal energy equal to zero.

ΔUisolated system = 0

Energy is Conserved

Ryan's chem wiki.jpg

ΔUsystem = -ΔUsurroundings

The signs of internal energy

  • Energy entering the system is POSITIVE (+), meaning heat is absorbed, q>0. Work is thus done on the system, w>0
  • Energy leaving the system is NEGATIVE (-), meaning heat is given off by the system, q<0 and work is done by the system, w<0
  • Since ΔUisolated system = 0, ΔUsystem = -ΔUsurroundings and energy is conserved.

Quick Notes

  • A system contains ONLY internal Energy
  • a system does NOT contain energy in the form of heat or work
  • Heat and work only exist during a change in the system
  • Internal energy is a state function

Contributors

  • Lorraine Alborzfar (UCD)

You must to post a comment.
Last modified
08:19, 5 Dec 2013

Tags

This page has no custom tags.

Classifications

(not set)
Vet2
Fundamental

CORE

TEXTMAPS

WIKI-TEXTS

HOMEWORK

WORKSHEETS

This material is based upon work supported by the National Science Foundation under Grant Numbers 1246120, 1525057, and 1413739.

Creative Commons License Unless otherwise noted, content in the UC Davis ChemWiki is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License. Permissions beyond the scope of this license may be available at copyright@ucdavis.edu. Questions and concerns can be directed toward Prof. Delmar Larsen (dlarsen@ucdavis.edu), Founder and Director. Terms of Use