If you like us, please share us on social media.

The latest UCD Hyperlibrary newsletter is now complete, check it out.

ChemWiki: The Dynamic Chemistry E-textbook > Physical Chemistry > Thermodynamics > State Functions > Kinetic Energy

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

- 1. Introduction
- 2. Kinetic Energy of a Bouncing Ball
- 3. Kinetic Energy of Atoms and Molecules
- 4. Kinetic Energy of Chemical Reactions
- 5. Relation Between Kinetic Energy and Thermal Energy
- 6. Rotational Kinetic Energy
- 7. Kinetic Energy Equation
- 8. Calculating the Kinetic Energy of Noble Gases
- 9. Practice Problems
- 10. Solutions
- 11. References
- 12. Outside Sources
- 13. Contributors

Kinetic energy is the energy of motion. *Kinetic* in Greek translates to "motion." The kinetic energy of an object depends on two factors: mass (m) and velocity (v). The mass of an object can be measured in kilograms (kg) and velocity of the object in meters per second(m/s).

The relationship between work and energy is visible when we compare the units of the two quantities. Since kinetic energy of an object is dependent upon mass (m) and velocity (v), the equation for kinetic energy is:

.

Work is dependent on mass, acceleration, and distance. The equation for work is:

When the units for both equations are added together the resulting units are kg m 2 s-2 which translated to the SI unit of energy called joule (J).

For example, if we were to pick up a bouncing ball from the ground and bring it up to a height of 6 feet, we would have to apply a force over six feet to overcome the gravitational force pulling the ball down. The work done over the six feet is then stored in the ball in terms of potential energy, which can be simply defined as the potential to do work if the ball is released. When the ball is released it falls down, pulled by gravitational force. The potential energy the ball had when it was at rest at six feet gets converted into kinetic energy as the ball falls to the ground. Potential energy gets converted into kinetic energy because when the ball falls it is no longer at rest, but in motion. Kinetic energy is at its highest right before the ball hits the ground. Once the ball bounces off the ground, kinetic energy begins to decrease because the ball slows down. As the ball comes up after hitting the ground potential energy increases because the height of the ball increases.

For a chemical reaction to occur there must be collisions between atoms or molecules to form a product. In order for the collisions to occur the atoms or molecules must have enough kinetic energy. The average kinetic energy of molecules can be measured in terms of temperature. Molecules with a high temperature have a greater kinetic energy than molecules with a low temperature. For example as the temperature of a gas begins to increase, the molecules of that solution begin to move faster, causing kinetic energy to increase.

Chemical reactions can either release energy (exothermic) or absorb energy (endothermic). During an exothermic reaction stored heat is released. When a chemical reaction releases energy, potential energy is converted into kinetic energy. When a chemical reaction absorbs energy, kinetic energy is converted into potential energy.

As discussed earlier, Kinetic energy is the energy of motion of all objects that can be defined by the equation

.

Thermal energy on the other hand is the kinetic energy of atoms and molecules of matter. We can find the thermal energy of atoms and molecules by measuring their temperature. As temperature increases, thermal energy of the atoms and molecules increases and as temperature decreases thermal energy of the atoms and molecules decreases.

Rotational kinetic energy is similar to the kinetic energy of an object traveling in a straight line, but rotational kinetic energy is represented in a different context. The mass of a rotational object is moving in a circle rather than a straight line. Since the object is rotating its speed depends on the distance from the center of the object (radius) and angular speed. The equation for rotational kinetic energy is

.

with the moment of inertia, I, is equal to m (mass) x r^{2}(radius).

For example a spinning wheel has a moment of interia of 7.2 and an angular speed of 10 m/s, its rotational kinetic energy would be equal to 360.

The equation for kinetic energy is:

.

Calculate the kinetic energy of a 40 kg object traveling 15 m/s.

Solution: mass= 40kg, velocity= 15 m/s, plug in these number into the kinetic energy equation

Calculate the kinetic energy of a 40 kg object traveling 30 m/s

Solution:

As you double the velocity of an object its kinetic energy increases by four times, so the velocity of an object has a lot more impact on kinetic energy than the mass of an object.

The kinetic energy of gases can be calculated using the equation:

,

where n is the moles of the gas, R is the gas constant 8.3145 J mole^{-1} K^{-1}, and T is temperature in kelvin

Example: A 5g sample of He has a temperature of 100K, calculate the kinetic energy of the He atoms

Solution: convert 5g of He to moles of He 5g/ 4.00260g = 1.25 moles of He, then plug in 100k for T, and 8.3145 for R

- Kinetic energy is dependent upon which two factors?
- Work is dependent upon which three factors?
- If you were to pick up a bike from the ground to six feet in the air how much of a force would you have to apply?
- When the bike is held at six feet in the air, does it have kinetic or potential energy?
- How is the average kinetic energy of molecules measured?
- Do molecules with a high temperature or low temperature have a greater kinetic energy? state why
- What happens in terms of potential and kinetic energy when a reaction is exothermic?
- What is the difference between kinetic energy and thermal energy?
- Calculate the kinetic energy of a 100 kg football player running with a velocity of 10 m/s
- A 2 grams sample of Ne has a temperature of 200k, calculate the KE of the Ne atoms.

- Kinetic energy is dependent on mass and velocity of an object.
- Work is dependent on mass, acceleration, and distance.
- To pick up a bike six feet, you would have to apply a force of six feet to overcome the gravitational force.
- When the bike is held six feet in the air, it has potential energy because if dropped it has the "potential" to do work and it is at rest.
- Average kinetic energy of molecules is measured in taking the temperature of the molecules in motion.
- Molecules with a high temperature have a greater kinetic energy than molecules with a low temperature, because the higher the temperature the faster the molecules move.
- When a reaction is exothermic, energy is released, because potential energy gets converted into kinetic energy.
- Kinetic energy is a generalized way of looking at the energy of all objects, while thermal energy is more specific because it deals with the kinetic energy of atoms and molecules
- Convert 2 grams of Ne into moles of NE, you get 0.91743 moles Ne, then plug in information into equation

- Petrucci, Harwood, Herring, Madura. General Chemistry Principles & Modern Applications. Prentice Hall. New Jersey, 2007
- Viegas, Jennifer.
*Kinetic And Potential Energy: Understanding Changes Within Physical Systems*. Rosen Group, 2004. - Chang, Raymond.
__General Chemistry: The Essential Concepts__. McGraw-Hill Science/Engineering/Math, 2007 - Bouncing Ball Image and Rotating Axel from http://commons.wikimedia.org/w/index.php?title=Special%3ASearch&search=kinetic+energy

- Eureka! Episode 9 - Kinetic Energy http://www.youtube.com/watch?v=zhX01toLjZs
- Eureka! Episode 10 - Potential Energy http://www.youtube.com/watch?v=Rn470XtSYK0&feature=related
- Potential Energy: Wile E Coyote & Roadrunner http://www.youtube.com/watch?v=Jnj8mc04r9E&feature=related
- Bill Nye The Science Guy on Energy (Full Clip) http://www.youtube.com/watch?v=0ASLLiuejAo&feature=related
- Potential and Kinetic Energy http://www.youtube.com/watch?v=8abzpXCjyjA&feature=related
- Potential and Kinetic Energy http://www.youtube.com/watch?v=qZ4FFWvZtyo&feature=related
- Physics II P- Rotational Kinetic Energy (a) http://www.youtube.com/watch?v=rXWgvUsXCuU
- Physics II P- Rotational Kinetic Energy (b) http://www.youtube.com/watch?v=cPG3nFwVoik&feature=related
- Energy Calculator - http://www.mhi-inc.com/Converter/Energy%20Converter.htm

- Harjeet Bassi (UCD)

Last Modified

13:15, 29 Dec 2013

**Analytical Chemistry**

**Biological Chemistry**

**Inorganic Chemistry**

**Organic Chemistry**

**Physical Chemistry**

**Theoretical Chemistry**

**Cal Poly Pomona**

**Diablo Valley College**

**Florida State U**

**Hope College**

**Howard University**

**Purdue**

**Sacramento City College**

**UC Davis**

**UC Irvine**

**Zumdahl 9 ^{ed}**

An NSF funded Project

- © Copyright 2014 Chemwiki

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