CHEM 139: Zumdahl Chapter 10 page 1 of 6 CHAPTER 10: ENERGY Active Learning Questions: 2-3, 5-6; End-of-Chapter Problems: 2-14, 21 10.1 THE NATURE OF ENERGY Energy: the ability to do work or produce heat potential energy (PE): energy due to position or its composition (chemical bonds) – A 10-lb bowling ball has higher PE when it is 10 feet off the ground compared to 10 inches off the ground → Greater damage on your foot after falling 10 feet compared to falling only 10 inches – In terms of chemical bonds, the stronger the bond, → more energy is required to break the bond, → the higher the potential energy of the bond kinetic energy (KE): energy associated with an object’s motion – e.g. a car moving at 55 mph has much greater KE than the same car moving at 15 mph → A car traveling 55 mph can cause more damage than a car traveling 15 mph. The Law of Conservation of Energy: In a chemical reaction, energy is neither created nor destroyed, so the total energy of the reactants must equal the total energy of the products. → Energy is simply converted from one form to another in a chemical reaction. Six Forms of Energy: heat, light, chemical, electrical, mechanical, and nuclear – Each can be converted to another. Example: Identify at least two types of energy involved for each of the following: 1. When you turn on a lamp 2. When using solar panels 3. At the Springfield Power Plant in The SimpsonsCHEM 139: Zumdahl Chapter 10 page 2 of 6 Energy changes accompany physical and chemical changes due to changes in potential and kinetic energy. Kinetic Energy and Physical States Solids have the lowest KE of the three physical states – Highest attraction between particles → particles are fixed Liquids have slightly higher KE than solids – Particles are still attracted to each other but can move past one another → particles are less restricted Gases have greatest KE compared to solids and liquids – Attractive forces completely overcome, so particles fly freely within container → particles are completely unrestricted 10.2 TEMPERATURE AND HEAT Temperature: A measure of the average kinetic energies of the particles in a substance – i.e., a measure of the random motions of the particles in a substance Heat: A measure of the total energy of the particles in a system (also called thermal energy) Example: Consider two beakers containing boiling water. Beaker A contains 100.0 mL of water while beaker B contains 500.0 mL of water. a. Which beaker contains water with a higher temperature? Explain. b. Which beaker contains water with a higher thermal energy? Explain.CHEM 139: Zumdahl Chapter 10 page 3 of 6 Heat: Energy that is transferred from a body at a higher temperature to one at a lower temperature → heat always transfers from the hotter to the cooler object! – "heat flow" means heat transfer Heat Transfer and Temperature – An object becomes hotter by gaining heat. – An object becomes colder by losing heat—i.e., when you “feel cold”, you are losing heat! Ex. 1: Fill in the blanks to indicate how heat is transferred: a. You burn your hand on a hot frying pan. ________________ loses heat, and ______________ gains the heat. b. Your tongue feels cold when you eat ice cream. ________________ loses heat, and ______________ gains the heat. Ex. 2: A small chunk of gold is heated in beaker #1, which contains boiling water. The gold chunk is then transferred to beaker #2, which contains room-temperature water. a. The temperature of the water in beaker #2 _____. ↑ ↓ stays the same b. Fill in the blanks: _____________ loses heat, and ____________ gains the heat. Ex. 3: Why do surfaces like a stone countertop or metal flatware (forks, knives, etc.) feel cold in restaurant? Aren’t they at room temperature like you? Explain. 10.3 EXOTHERMIC AND ENDOTHERMIC PROCESSES Energy and Chemical and Physical Change endothermic change: a physical or chemical change that requires energy or heat to occur – boiling water requires energy: H2O(l) + heat energy → H2O(g) – electrolysis of water requires energy: 2 H2O(l) + electrical energy → 2 H2(g) + O2(g) exothermic change: a physical or chemical change that releases energy or heat – water condensing releases energy: H2O(g) → H2O(l) + heat energy – hydrogen burning releases energy: 2 H2(g) + O2(g) → 2 H2O(g) + heat energyCHEM 139: Zumdahl Chapter 10 page 4 of 6 For physical changes, consider whether the reactants or products have more kinetic energy. – If the reactants have greater kinetic energy than the products → exothermic process. – If the products have greater kinetic energy than the reactants → endothermic process. system: that part of the universe being studied surroundings: the rest of the universe outside the system For chemical changes, observe if the surroundings (including you) feel hotter or colder after the reaction has occurred. – If the surroundings are hotter, the reaction released heat → exothermic reaction. – If the surroundings are colder, the reaction absorbed heat → endothermic reaction. Ex. 1: Circle all of the following changes that are exothermic: freezing vaporizing sublimation melting depositionCHEM 139: Zumdahl Chapter 10 page 5 of 6 Ex. 2: A student adds ammonium chloride (NH4Cl) salt to a test tube containing water and notices that the test tube feels colder as the ammonium chloride dissolves. Is this process exothermic or endothermic? Explain. Ex. 3: A student mixes two solutions, hydrochloric acid and sodium hydroxide, and notices the beaker with the substances feels hotter as they mix. Is this reaction exothermic or endothermic? Explain. Units of Energy calorie (cal): unit of energy used most often in the US – amount of energy required to raise the temperature of 1 g of water by 1˚C – But a nutritional calorie (abbreviated Cal) is actually 1000 cal: 1 Cal = 1 kcal joule (J): SI unit of energy – To recognize the size of a joule, note that 1 watt = 1 sJ → So a 100-watt light bulb uses 100 J every second. – Heat is also often reported in kilojoules (kJ), where 1 kJ = 1000 J – To