Basic Chemistry Continued

Energy The ability to do work or cause a change Two types of energy Kinetic energy ~ the energy of motion. Examples: falling, heat, light, electricity Potential energy ~ stored energy as a result of location or structure. Examples: rock sitting at the top of cliff, log waiting to be burned. Energy can be converted from one to the other.

Thermodynamics The following laws define how energy changes occur. The First Law of Thermodynamics (Law of Conservation)- energy is neither created nor destroyed. Energy can be changed from one form to another, but there is always as much energy as there was at the beginning. The Second Law of Thermodynamics- Whenever energy is used (changed from one form to another) some of it is wasted, usually as heat or light. Law of Degeneration- in all natural processes there is a net increase in disorder and a net loss of usable energy.

Entropy- an increase in randomness and loss of usable energy.

Kinetic energy of movement Figure 5.10_1 Fuel Energy conversion Waste products Heat energy Carbon dioxide Gasoline   Combustion Kinetic energy of movement Figure 5.10_1 Energy transformations in a car and a cell (part 1) Water Oxygen Energy conversion in a car 7

Energy for cellular work Water Figure 5.10_2 Fuel Energy conversion Waste products Heat energy Cellular respiration Glucose Carbon dioxide   ATP ATP Figure 5.10_2 Energy transformations in a car and a cell (part 2) Oxygen Energy for cellular work Water Energy conversion in a cell 8

Kinetic Energy of Molecules All molecules in a substance are moving. The amount of thermal energy in a substance determines how fast its molecules move and subsequently its physical state.

Potential Energy of a Molecule Each molecule has potential energy held in its chemical bonds

Glycerol Fatty acids Figure 3.8C A fat molecule (triglyceride) consisting of three fatty acids linked to glycerol 12

ATP: Adenosine Triphosphate Phosphate group P P P Adenine Ribose H2O Hydrolysis Figure 5.12A_s2 The structure and hydrolysis of ATP (step 2) P P P Energy ADP: Adenosine Diphosphate 13

Two types of chemical reactions, based on energy: endothermic ~ absorbs or requires energy (ex. photosynthesis) exothermic ~ gives off or releases energy (ex. cellular respiration)

Cells transform energy as they perform work Cells use oxygen in reactions that release energy from fuel molecules. In cellular respiration, the chemical energy stored in organic molecules is converted to a form that the cell can use to perform work. Student Misconceptions and Concerns Students with limited exposure to physics may have never understood the concepts of energy and the conservation of energy or distinguished between potential and kinetic energy. Understanding such broad and new abstract concepts requires time and concrete examples. Teaching Tips 1. In our daily lives, we rely upon many energy transformations. On our classroom walls, a clock converts electrical energy to mechanical energy to sweep the hands around the clock’s face (unless it is digital!). Our physical (mechanical) activities walking to and from the classroom rely upon the chemical energy from our diet. This chemical energy in our diet also helps us maintain a steady body temperature (heat). Consider challenging your students to come up with additional examples of such common energy conversions in their lives. 2. Some students can relate well to the concept of entropy as applied to the room where they live. Despite their cleaning up and organizing the room on a regular (or irregular) basis, the room becomes increasingly disorganized, a victim of entropy, until another energy input (or effort) is exerted to make the room more orderly again. Students might even get to know entropy as the “dorm room effect.” 3. The heat produced by the engine of a car is typically used to heat the car during cold weather. However, is this same heat available in warmer weather? Students are often unaware that their car “heaters” work very well in the summer too. Just as exercise can warm us when it is cold, the same extra heat is released when we exercise in warm conditions. A car engine in the summer struggles to dissipate heat in the same way that a human struggles to cool off after exercising when weather is warm. 4. Here is a question that might make cellular respiration a little more meaningful to your students. Ask your students why they feel warm when it is 30C (86F) outside if their core body temperature is 37C (98.6F). Shouldn’t they feel cold? The answer is, our bodies are always producing heat. At these higher temperatures, we are producing more heat than we need to maintain a core body temperature around 37C. Thus, we sweat and behave in ways that help release our extra heat generated in cellular respiration. © 2012 Pearson Education, Inc. 15

Chemical reactions either release or store energy Exergonic reactions release energy. These reactions release the energy in covalent bonds of the reactants. Burning wood releases the energy in glucose as heat and light. Cellular respiration involves many steps, releases energy slowly, and uses some of the released energy to produce ATP. Student Misconceptions and Concerns 1. Students with limited exposure to physics may have never understood the concepts of energy and the conservation of energy or distinguished between potential and kinetic energy. Understanding such broad and new abstract concepts requires time and concrete examples. 2. All too often we hear or read that some thing or reaction creates energy. We might hear or read that a power plant “produces” energy or that mitochondria “make” energy. Even in our classroom conversations, we may occasionally slip into this error. When discussing the first law of thermodynamics, consider emphasizing the inaccuracy of such statements. 3. Although typically familiar with the concept of dietary calories, students often struggle to think of calories as a source of potential energy. For many students, it is not clear that potential energy is stored in food as calories. Teaching Tips 1. The same mass of fat stores nearly twice as many calories (about 9 kcal per gram) as an equivalent mass of protein or carbohydrates (about 4.5–5 kcal per gram). Thus, when comparing equal masses of fat, protein, and lipid, the fat has nearly twice the potential energy. Fat is therefore an efficient way to store energy in animals and many plants. To store an equivalent amount of energy in the form of carbohydrates or proteins would require about twice the mass, adding a significant burden to the organism’s structure. (For example, if you were 20 lbs overweight, you would be nearly 40 lbs overweight if the same energy were stored as carbohydrates or proteins instead of fat). 2. The amount of energy each adult human needs to generate the ATP required in a day is tremendous. Here is a calculation that has impressed many students. Depending upon the size and activity of a person, a human might burn 2,000 dietary calories (kilocalories) a day. This is enough energy to raise the temperature of 20 liters of liquid water from 0 to 100C. This is something to think about the next time you heat water on the stove! If you can bring in ten 2-liter bottles, you can help students visualize how much liquid water can be raised from 0 to 100C. (Note: 100 calories raises about 1 liter of water 100C, but it takes much more energy to melt ice or to convert boiling water into steam.) © 2012 Pearson Education, Inc. 16

Amount of energy released Reactants Amount of energy released Potential energy of molecules Energy Products Figure 5.11A Exergonic reaction, energy released 17

Chemical reactions either release or store energy An endergonic reaction requires an input of energy and yields products rich in potential energy. Endergonic reactions begin with reactant molecules that contain relatively little potential energy but end with products that contain more chemical energy. Student Misconceptions and Concerns 1. Students with limited exposure to physics may have never understood the concepts of energy and the conservation of energy or distinguished between potential and kinetic energy. Understanding such broad and new abstract concepts requires time and concrete examples. 2. All too often we hear or read that some thing or reaction creates energy. We might hear or read that a power plant “produces” energy or that mitochondria “make” energy. Even in our classroom conversations, we may occasionally slip into this error. When discussing the first law of thermodynamics, consider emphasizing the inaccuracy of such statements. 3. Although typically familiar with the concept of dietary calories, students often struggle to think of calories as a source of potential energy. For many students, it is not clear that potential energy is stored in food as calories. Teaching Tips 1. The same mass of fat stores nearly twice as many calories (about 9 kcal per gram) as an equivalent mass of protein or carbohydrates (about 4.5–5 kcal per gram). Thus, when comparing equal masses of fat, protein, and lipid, the fat has nearly twice the potential energy. Fat is therefore an efficient way to store energy in animals and many plants. To store an equivalent amount of energy in the form of carbohydrates or proteins would require about twice the mass, adding a significant burden to the organism’s structure. (For example, if you were 20 lbs overweight, you would be nearly 40 lbs overweight if the same energy were stored as carbohydrates or proteins instead of fat). 2. The amount of energy each adult human needs to generate the ATP required in a day is tremendous. Here is a calculation that has impressed many students. Depending upon the size and activity of a person, a human might burn 2,000 dietary calories (kilocalories) a day. This is enough energy to raise the temperature of 20 liters of liquid water from 0 to 100C. This is something to think about the next time you heat water on the stove! If you can bring in ten 2-liter bottles, you can help students visualize how much liquid water can be raised from 0 to 100C. (Note: 100 calories raises about 1 liter of water 100C, but it takes much more energy to melt ice or to convert boiling water into steam.) © 2012 Pearson Education, Inc. 18

Amount of energy required Products Amount of energy required Potential energy of molecules Energy Reactants Figure 5.11B Endergonic reaction, energy required 19

Chemical reactions either release or store energy Photosynthesis is a type of endergonic process. Energy-poor reactants, carbon dioxide, and water are used. Energy is absorbed from sunlight. Energy-rich sugar molecules are produced. Student Misconceptions and Concerns 1. Students with limited exposure to physics may have never understood the concepts of energy and the conservation of energy or distinguished between potential and kinetic energy. Understanding such broad and new abstract concepts requires time and concrete examples. 2. All too often we hear or read that some thing or reaction creates energy. We might hear or read that a power plant “produces” energy or that mitochondria “make” energy. Even in our classroom conversations, we may occasionally slip into this error. When discussing the first law of thermodynamics, consider emphasizing the inaccuracy of such statements. 3. Although typically familiar with the concept of dietary calories, students often struggle to think of calories as a source of potential energy. For many students, it is not clear that potential energy is stored in food as calories. Teaching Tips 1. The same mass of fat stores nearly twice as many calories (about 9 kcal per gram) as an equivalent mass of protein or carbohydrates (about 4.5–5 kcal per gram). Thus, when comparing equal masses of fat, protein, and lipid, the fat has nearly twice the potential energy. Fat is therefore an efficient way to store energy in animals and many plants. To store an equivalent amount of energy in the form of carbohydrates or proteins would require about twice the mass, adding a significant burden to the organism’s structure. (For example, if you were 20 lbs overweight, you would be nearly 40 lbs overweight if the same energy were stored as carbohydrates or proteins instead of fat). 2. The amount of energy each adult human needs to generate the ATP required in a day is tremendous. Here is a calculation that has impressed many students. Depending upon the size and activity of a person, a human might burn 2,000 dietary calories (kilocalories) a day. This is enough energy to raise the temperature of 20 liters of liquid water from 0 to 100C. This is something to think about the next time you heat water on the stove! If you can bring in ten 2-liter bottles, you can help students visualize how much liquid water can be raised from 0 to 100C. (Note: 100 calories raises about 1 liter of water 100C, but it takes much more energy to melt ice or to convert boiling water into steam.) © 2012 Pearson Education, Inc. 20