Go to Section : Matter and Energy Have you ever sat around a campfire or watched flames flicker in a fireplace? The burning of wood is a chemical reaction—a process that changes one set of chemicals into another set of chemicals. A chemical reaction always involves changes in chemical bonds that join atoms in compounds. The elements or compounds that enter into a chemical reaction are called reactants. The elements or compounds produced by a chemical reaction are called products. As wood burns, molecules of cellulose are broken down and combine with oxygen to form carbon dioxide and water vapor, and energy is released. Section 2-4 Interest Grabber
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Matter and Energy
Have you ever sat around a campfire or watched flames flicker in a fireplace? The burning of wood is a chemical reaction—a process that changes one set of chemicals into another set of chemicals. A chemical reaction always involves changes in chemical bonds that join atoms in compounds. The elements or compounds that enter into a chemical reaction are called reactants. The elements or compounds produced by a chemical reaction are called products. As wood burns, molecules of cellulose are broken down and combine with oxygen to form carbon dioxide and water vapor, and energy is released.
Section 2-4
Interest Grabber
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1. What are the reactants when wood burns?
2. What are the products when wood burns?
3. What kinds of energy are given off when wood burns?
4. Wood doesn’t burn all by itself. What must you do to start a fire? What does this mean in terms of energy?
5. Once the fire gets started, it keeps burning. Why don’t you need to keep restarting the fire?
Section 2-4
Interest Grabber continued
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2–4 Chemical Reactions and EnzymesA. Chemical Reactions
B. Energy in Reactions
1. Energy Changes
2. Activation Energy
C. Enzymes
D. Enzyme Action
1. The Enzyme-Substrate Complex
2. Regulation of Enzyme Activity
Section 2-4
Section Outline
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Chemical reactions
•A chemical reaction is a process that changes one set of chemicals into another set of chemicals by changing chemical bonds.•The reactants are the elements or compounds that enter into a chemical reaction•The products are the elements or compounds produced by a chemical reaction.•On notes label reactants and products
2-4 Chemical reactions and enzymes
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Energy in reactions
•Energy is either released or absorbed when chemical bonds are formed or broken.
•Activation energy is the energy needed to get a reaction started.
2-4 Chemical reactions and enzymes
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Energy-Absorbing Reaction Energy-Releasing Reaction
Products
Products
Activation energy
Activation energy
Reactants
Reactants
Section 2-4
Figure 2-19 Chemical Reactions
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Energy-Absorbing Reaction Energy-Releasing Reaction
Products
Products
Activation energy
Activation energy
Reactants
Reactants
Section 2-4
Figure 2-19 Chemical Reactions
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Enzymes
•A catalyst is a substance that speeds up the rate of a chemical reaction•An enzyme is a protein that acts as a biological catalyst•Enzymes speed up reaction by lowering the activation energy of the chemical reaction•Show video 2D
2-4 Chemical reactions and enzymes
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Reaction pathwaywithout enzyme Activation energy
without enzyme
Activationenergywith enzymeReaction pathway
with enzyme
Reactants
Products
Section 2-4
Effect of Enzymes
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Enzyme Action
•Substrates are the reactants of enzyme-catalyzed reactions•An active site is the site on the enzyme where the substrate binds.•The active site and substrates in an enzyme-catalyzed reaction are often compared to a lock and key because the active site and substrate have complementary shapes and the fit is precise.
2-4 Chemical reactions and enzymes
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Glucose
Substrates
ATP
Substratesbind toenzyme
Substratesare convertedinto products
Enzyme-substratecomplex
Enzyme(hexokinase)
ADPProducts
Glucose-6-phosphate
Productsare released
Section 2-4
Figure 2-21 Enzyme Action
Active site
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Glucose
Substrates
ATP
Substratesbind toenzyme
Substratesare convertedinto products
Enzyme-substratecomplex
Enzyme(hexokinase)
ADPProducts
Glucose-6-phosphate
Productsare released
Section 2-4
Figure 2-21 Enzyme Action
Active site
Go to Section:
Glucose
Substrates
ATP
Substratesbind toenzyme
Substratesare convertedinto products
Enzyme-substratecomplex
Enzyme(hexokinase)
ADPProducts
Glucose-6-phosphate
Productsare released
Section 2-4
Figure 2-21 Enzyme Action
Active site
Go to Section:
Glucose
Substrates
ATP
Substratesbind toenzyme
Substratesare convertedinto products
Enzyme-substratecomplex
Enzyme(hexokinase)
ADPProducts
Glucose-6-phosphate
Productsare released
Section 2-4
Figure 2-21 Enzyme Action
Active site
Videos
Click a hyperlink to choose a video.
Atomic Structure
Energy Levels and Ionic Bonding
Covalent Bonding
Enzymatic Reactions
Click the image to play the video segment.
Video 1
Atomic Structure
Click the image to play the video segment.
Video 2
Energy Levels and Ionic Bonding
Click the image to play the video segment.
Video 3
Covalent Bonding
Click the image to play the video segment.
Video 4
Enzymatic Reactions
Career links on forensic scientists
Interactive test
Articles on organic chemistry
For links on properties of water, go to www.SciLinks.org and enter the Web Code as follows: cbn-1022.
For links on enzymes, go to www.SciLinks.org and enter the Web Code as follows: cbn-1024.
Go Online
1. Give an example of solid matter.
Sample answers: books, desks, chairs
2. Give an example of liquid matter.
Sample answers: water, milk
3. Give an example of gaseous matter.
Sample answers: air, helium in a balloon
4. Is all matter visible?
No
5. Does all matter take up space?
Yes
Interest Grabber Answers
Interest Grabber Answers
1. Working with a partner, make a list of ten things that have water in them.
Possible answers: bodies of water, rain and snow, soft drinks and other beverages, juicy foods such as fruits, and so on.
2. Exchange your list for the list of another pair of students. Did your lists contain some of the same things? Did anything on the other list surprise you?
Students’ answers will likely be similar, but not exactly alike.
3. Did either list contain any living things?
Students’ lists may include plants, animals, or other living things.
Interest Grabber Answers
1. On a sheet of paper, make a list of at least ten things that contain carbon.
Students will likely know that charcoal and coal contain carbon. They may also list carbohydrates (starches and sugars), oil, gasoline, wood, or carbon dioxide.
2. Working with a partner, review your list. If you think some things on your list contain only carbon, write “only carbon” next to them.
Students will say that charcoal and coal contain only carbon. While these materials do contain small amounts of other elements, such as sulfur, they are composed mostly of carbon.
3. If you know other elements that are in any items on your list, write those elements next to them.
Students may know that many carbon compounds also contain oxygen and/or hydrogen.
Interest Grabber Answers
1. What are the reactants when wood burns?Reactants are oxygen and cellulose.
2. What are the products when wood burns?Products are carbon dioxide and water.
3. What kinds of energy are given off when wood burns?Light and heat are given off. Some students may also mention sound (the crackling of a fire).
4. Wood doesn’t burn all by itself. What must you do to start a fire? What does this mean in terms of energy?To start a fire, you must light it with a match and kindling. You are giving the wood some energy in the form of heat.
5. Once the fire gets started, it keeps burning. Why don’t you need to keep restarting the fire?Once the fire gets going, it gives off enough heat to start more of the wood burning.
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