The composition eg color density 17 copyright 2007

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Unformatted text preview: observed without changing the composition (e.g., color, density). 17 Copyright © 2007 by Concise Books Publishing LLC. Visit us at www.concisechem.com to download other free chapters from "The Concise Guide to Chemistry." CHAPTER 3. 1.4 1: INTRODUCTION TO CHEMISTRY Gram of anything is a gram. The second part of the question is a density question. We know that density of a rock is much higher than that of cotton, which means that the mass of a rock is much higher than that of cotton when we measure equal volumes of each. Energy Do you still remember the challenge posed earlier where you were asked to name something that is not made from chemicals (i.e. something that is not matter)? Well, if you were able to come up with something that wasn’t matter (e.g., light), then you just named a form of energy. The universe as we know it is composed of matter and energy. Change in matter always involves change in energy; hence chemistry is concerned with both matter and energy. The difference between the two is not as obvious as it might seem. 1.4.1 Mass & Weight In common language, we use mass and weight interchangeably, but in the scientific language they are quite different. • Mass is the measure of the amount of material in an object. It does not depend on the location of the object. • It is different from weight, which is a measure of gravitational force that a large body (e.g. earth) exerts on an object, and does depend on the location. Inquisitive Chemist 1.7: Weight on different planets. Planet Mars is about 1/3 as dense as Earth, exerting about 1/3 of the gravity on an object. Hence, if your weight on Earth were 150 lbs, your weight on Mars would be ~ 38 lbs. To explore your weight on different planets, moons and stars, go to http://www.exploratorium.edu/ronh/weight/. 1.4.2 Energy has Mass For many years, mass was used as the distinguishing characteristic between matter and energy. That is, until early in the 20th century, when Albert Einstein pointed out with his famous equation that energy (potential for causing changes; ability to do work) has mass as well. Einstein’s equation showed that matter of mass m possesses an intrinsic rest mass energy given by mc2. E = mc2 where E m c units J = energy = mass kg = = speed of light in vacuum 2.99792458 x 108 m⋅s-1 The fact that energy has mass was later demonstrated with a showcase of bending light ray of a distant star as it passed close to the sun. If light has no mass, there should not have been any gravitational attraction of the light ray toward the sun. 18 Copyright © 2007 by Concise Books Publishing LLC. Visit us at www.concisechem.com to download other free chapters from "The Concise Guide to Chemistry." CHAPTER 1.4.3 1: INTRODUCTION TO CHEMISTRY Energy & Matter Matter and energy are intimately related. • We can see from Einstein’s equation that it is possible to convert matter to energy (observed in reactions involving nuclei of atoms such as fusion a...
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