Reading Essentials Energy Changes in Chemical Reactions PDF

LESSON 3 Matter: Properties and Changes...

LESSON 3 Matter: Properties and Changes Energy Changes in Chemical Reactions Key Concept Why do some reactions What do you think? Read the two statements below and decide give off thermal energy whether you agree or disagree with them. Place an A in the Before and some absorb thermal column if you agree with the statement or a D if you disagree. After energy? you’ve read this lesson, reread the statements to see if you have changed your mind. Before Statement After Reactions that release energy require energy to get started. Energy can be created during a chemical reaction. Mark the Text Where does the energy in a chemical Create a Quiz Write a quiz question for each reaction come from? paragraph. Answer the When an injury occurs, someone might place a medical question with information instant cold or hot pack on the injury. How do these packs from the paragraph. Then become hot or cold so quickly? Each pack has a different work with a partner to quiz each other. chemicals inside. When the chemicals are mixed in the hot and cold packs, a temperature change happens. For the temperature of the packs to change, the energy of the system has to change. Copyright © McGraw-Hill Education. Permission is granted to reproduce for classroom use. This energy has to either come from the chemical bonds holding the atoms together or the surrounding environment. Energy Transfers All matter is constantly moving. The more energy particles have, the more they move and collide with one another. When they collide with each other with the right amount of force, the bonds between the atoms break. The breaking of chemical bonds requires energy. When individual atoms collide and form bonds, energy is released. The atoms Scientific Vocabulary release this energy to the environment as light or heat. Chemical dependent potential energy is the energy released when atoms form (adjective) determined by bonds. The chemical potential energy is dependent on the something else arrangement and strength of the bonds. Reading Essentials Matter: Properties and Changes 11 THIS MATERIAL IS PROVIDED FOR INDIVIDUAL EDUCATIONAL PURPOSES ONLY AND MAY NOT BE DOWNLOADED OR FURTHER DISTRIBUTED.  How does energy input and output compare between chemical reactions? If all chemical reactions both absorb energy and release energy, then how can you explain the temperature changes in the hot and cold packs? The transfer of energy can be tracked as energy flows through a system. When the hot pack became hot, it was because energy was released by the chemical reaction to the surroundings. The cold pack became cold because it absorbed energy from the surroundings. Energy in Chemical Reactions Not all bonds release and absorb the same amount of energy. Some atoms release a high amount of energy when they form compounds. For instance, the chemical reactions that occurs in a firework release a large amount of energy in the form of thermal energy, light, and sound. Other compounds require a lot of energy to break apart. The elements and compounds involved in the chemical reaction determine if an overall change in energy is noticeable. Scientists connected the evidence of temperature change to the explanation of thermal energy transfers. Energy Absorbed On a very warm day, have you ever heard someone say that the sidewalk was hot enough to fry an egg? To fry, the egg must absorb energy. Chemical reactions where more energy is required to break the bonds of the reactants than is released when products form are endothermic reactions. For an endothermic reaction to continue, energy must be constantly added. reactants + thermal energy → products The overall reaction absorbs energy. This is why thermal energy appears on the side with the reactants in the chemical Copyright © McGraw-Hill Education. Permission is granted to reproduce for classroom use. equation above. Academic Vocabulary Energy Released Some chemical reactions release energy as opposed to as opposed to absorbing it. In an exothermic reaction more (phrase) rather than; energy is released when the products form than is required to instead of break the bonds in the reactants. Word Origin reactants → products + thermal energy exothermic The overall reaction releases energy. This is why thermal from Greek exo-, means energy appears on the side with the products in the chemical “outside”; therm, means “heat” equation above. The bonds of the reactants contain more energy than the bonds of the products. 12 Matter: Properties and Changes Reading Essentials THIS MATERIAL IS PROVIDED FOR INDIVIDUAL EDUCATIONAL PURPOSES ONLY AND MAY NOT BE DOWNLOADED OR FURTHER DISTRIBUTED.  Life Science Connection Energy changes in chemical reactions do not just create changes in temperature. They also Scientific Vocabulary provide the energy that we use every day. All living organisms organism harness chemical reactions to supply their cells with energy. (noun) a living thing, such Plants and some unicellular organisms use the Sun’s energy for as an animal or plant photosynthesis. During photosynthesis, plant cells use the energy from sunlight to split water into hydrogen atoms and oxygen Scientific Vocabulary atoms. The cells then release the gaseous oxygen atoms into the harness (verb) to use something atmosphere. A second set of reactions involves energy, hydrogen, for a particular purpose and carbon dioxide from the air. The energy absorbed by the cells breaks the bonds between the hydrogen molecules and the Scientific Vocabulary carbon dioxide molecules. The sugar glucose, a molecule with 6 gaseous carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms (C6H12O6) (adjective) having the is formed. The plant can then store the glucose for later use. form of gas When the plant is eaten by animals, the animals obtain the glucose molecules from the plant cells. When the chemical bonds of glucose are broken, by either a plant or an animal, energy is released. This process is called cellular respiration. The chemical bonds of glucose molecules break, which releases energy cells can then use. The photosynthesis/cellular respiration combination is a process in which plants absorb radiant energy from the Sun and transfer it into the chemical bonds of the molecule glucose. When other organisms eat the plant, the glucose bonds break and energy is released. Concentration What happens to a plant if any one of the reactants needed for photosynthesis is reduced? Can the reaction happen in the same way? No, if the amount of carbon dioxide, water, or light is reduced, the plant will not function normally. The plant needs to have enough concentration of all the reactants to function properly. This is also true of other reactions, like the hot and cold packs. The correct concentration Copyright © McGraw-Hill Education. Permission is granted to reproduce for classroom use. of reactants will lead to the most products. Think of a crowded hallway. Because the concentration of people is higher in the crowded hallway than in an empty hallway, people probably collide more often. Similarly, increasing the concentration of one or more reactants increases collisions between particles. More collisions result in a faster reaction rate. When particles are closer together, more collisions occur. Reading Essentials Matter: Properties and Changes 13 THIS MATERIAL IS PROVIDED FOR INDIVIDUAL EDUCATIONAL PURPOSES ONLY AND MAY NOT BE DOWNLOADED OR FURTHER DISTRIBUTED.  Conserving Energy As you have seen, when atoms collide with each other, they transfer energy and chemical reactions occur. Some reactions absorb more energy than they give off, and others release more energy than they absorb. Energy is Academic Vocabulary constantly transferring between the surroundings and chemical overall bonds. Yet the total amount of overall energy remains the same. (adjective) considered as The law of conservation of energy states that even though a whole; in general energy is always transferring, energy is not created and energy is not destroyed. Energy is constantly being reused. In a hot pack, energy moves to the environment as it is released by the chemical bonds of the reactants. In a cold pack, energy is absorbed. So, the energy moves from the environment into the chemical bonds of the products. Life Science Connection The laws of conservation of energy and matter apply to both the physical and living environments. Plants store glucose molecules in their tissues. When plants are eaten by animals, energy and matter transfer to the consumer. One way energy can return to the environment is in the form of thermal energy given off by organisms. Another way is when plants and animals die, the energy and matter contained in their tissues is recycled by decomposers. Food webs model how matter and energy are transferred through ecosystems. Reread the statements at the beginning of the lesson. Fill in the After column with an A if you agree with the statement or a D if you disagree. Did you change your mind? Copyright © McGraw-Hill Education. Permission is granted to reproduce for classroom use. 14 Matter: Properties and Changes Reading Essentials THIS MATERIAL IS PROVIDED FOR INDIVIDUAL EDUCATIONAL PURPOSES ONLY AND MAY NOT BE DOWNLOADED OR FURTHER DISTRIBUTED.