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MindTouch
Copyright (c) 2006-2014 MindTouch Inc.
http://mindtouch.com

This file and accompanying files are licensed under the MindTouch Master Subscription Agreement (MSA).

At any time, you shall not, directly or indirectly: (i) sublicense, resell, rent, lease, distribute, market, commercialize or otherwise transfer rights or usage to: (a) the Software, (b) any modified version or derivative work of the Software created by you or for you, or (c) MindTouch Open Source (which includes all non-supported versions of MindTouch-developed software), for any purpose including timesharing or service bureau purposes; (ii) remove or alter any copyright, trademark or proprietary notice in the Software; (iii) transfer, use or export the Software in violation of any applicable laws or regulations of any government or governmental agency; (iv) use or run on any of your hardware, or have deployed for use, any production version of MindTouch Open Source; (v) use any of the Support Services, Error corrections, Updates or Upgrades, for the MindTouch Open Source software or for any Server for which Support Services are not then purchased as provided hereunder; or (vi) reverse engineer, decompile or modify any encrypted or encoded portion of the Software.

A complete copy of the MSA is available at http://www.mindtouch.com/msa

# 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

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

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)

08:19, 5 Dec 2013

## Classifications

Vet2
Fundamental

### Textbook Maps

An NSF funded Project