Chapter 3 Resource: Matter and its Changes

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Name Date Class Meeting Individual Needs 2 Enrichment One chemical property is the sensitivity of a substance to heat. Some chemicals might change form when their temperature changes; others might undergo chemical reactions with other substances. When these changes result in a change in color, the chemicals involved are called thermochromic. (Thermo means “heat,” and chrom means “color.”) Thermochromic Labels Some thermochromic chemicals undergo irreversible changes when they are heated. In other words, once the color change occurs, the chemical does not have the ability to return to its original color even after it is cooled. These types of thermochromic chemicals are being used on a new type of labels for fresh meats. All fresh meat contains a certain amount of bacteria. Because the bacteria grow very slowly at cool temperatures, the meat is safe to eat for a certain amount of time as long as it is kept refrigerated. However, if the meat is exposed to high temperatures anywhere on its way from a packing plant to a grocery store to your kitchen, the bacteria in the meat will grow much more quickly. They might even build up to levels that would make the meat unsafe to consume. Color Change A thermochromic label is designed to help people tell if meat has been exposed to high temperatures. When the meat is packaged, a thermochromic label is placed on the outside. Using Chemical Reactions on Food Labels The label is then activated, which allows two or more chemicals inside the label to mix. If the temperature increases to a certain level, a reaction will occur between these chemicals that causes the label to change color. (For example, some labels change from white to black or from green to yellow.) This color change tells customers that the meat is not safe to eat. Time-Temperature Indicators The chemicals in thermochromic labels used on meat are not only sensitive to temperature. They are also sensitive to time. For this reason, these labels are sometimes called TTI (Time-Temperature Indicator) labels. Regular labels on meat usually have an expiration or “sell-by” date. After this date, the meat is no longer safe to be sold. A TTI label is not marked with a date, however. Instead, the label changes color after a certain amount of time has passed (regardless of whether the meat has been exposed to high temperatures). Because different combinations of chemicals have different sensitivities to temperature and time, scientists can design TTI labels that will change color at almost any temperature or after almost any period of time. This allows TTI labels to be used on a variety of different foods, including milk, eggs, and even fresh fruit and vegetables. You will probably be seeing more of these labels in the near future. 1. Why is it important that the color change in a thermochromic meat label is irreversible 2. How is a thermochromic chemical similar to an acid-base indicator How are they different 3. Is sensitivity to time a physical property or a chemical property Explain. 4. Think of another application for thermochromic chemicals besides food labels. On a separate sheet of paper write a short paragraph describing this use. Will this application use chemicals that undergo a reversible or irreversible color change Who would be likely to use or benefit from the application Copyright © Glencoe/McGraw-Hill, a division of the McGraw-Hill Companies, Inc. 30 Matter and Its Changes
Name Date Class Note-taking Worksheet Matter and Its Changes Section 1 Physical Properties and Changes A. Physical _________________—any characteristic of matter that can be observed or measured without changing the identity of the matter; a physical _______________ makes physical properties change, but identity remains the same. 1. Length and _____________ (amount of material in an object) are properties that can be measured. 2. _______________ is a measure of how much space an object takes up; ________________ is the amount of mass a material has for a given volume. 3. Density changes as pressure or temperature change. B. Solid, liquid, gas, and plasma are four _________________________; state of matter depends on its temperature and pressure. 1. Matter is made up of _________________________; solid particles have less energy than liquid particles, which have less energy than gas particles. Meeting Individual Needs 2. ________________ point—temperature at which a solid becomes a liquid; example: Copyright © Glencoe/McGraw-Hill, a division of the McGraw-Hill Companies, Inc. ice melting 3. ________________ point—temperature at which a liquid becomes a gas; example: water becoming steam C. _________________ properties can include luster, malleability, ductility, and magnetism. D. Physical properties can be used to identify, classify, and separate ___________________. Section 2 Chemical Properties and Changes A. Chemical _________________—characteristic that gives a substance the ability to undergo a change that results in a new substance 1. Flammability 2. Reacts with oxygen, ___________________, water, or other substances Matter and Its Changes 31
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Chapter 3 Resource: Matter and its Changes

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