Chapter 2 Energy - Mariano Marcos State University

 Energy Unit Two Engr. Jaerell Brent Pedro, RChT Instructor I [email protected] COLLEGE OF ARTS & SCIENCES Department of Physical Scien...

 Energy Unit Two Engr. Jaerell Brent Pedro, RChT Instructor I [email protected] COLLEGE OF ARTS & SCIENCES Department of Physical Sciences  CHAPTER 2 Energy 1. Introduction to Energy 3. Nuclear Chemistry and Energy a. Definition of Energy a. Radioactivity and Nuclear Reactions b. Forms and Units of Energy b. Kinetics of Radioactive Decay c. Heat and Work: Forms of Energy Transfer c. Nuclear Stability d. Energetics of Nuclear Reactions d. Heat Capacity and Specific Heat e. Transmutation, Fission, and Fusion e. Introduction to Calorimetry f. The Interaction of Radiation and Matter 2. Electrochemical Energy 4. Fuels a. Redox Reaction a. Meaning of Fuels b. Galvanic Cells b. Classification of Chemical Fuels c. Standard Reduction Potential c. Gaseous Fuels d. Batteries d. Liquid Fuels e. Corrosion e. Solid Fuels COLLEGE OF ARTS & SCIENCES Department of Physical Sciences Introduction to Energy Definition of Energy Energy – the capacity to supply heat or do work Work (w) – done when movement occurs against a restraining force w = Fd Heat (q) – energy that flows from a hotter to a colder object Everything is ENERGY! https://chem.libretexts.org/Courses/Oregon_Tech _PortlandMetro_Campus/OT_-_PDX_- _Metro%3A_General_Chemistry_I/08%3A_Therm ochemistry/8.01%3A_The_Basics_of_Energy Introduction to Energy Forms and Units of Energy Because energy takes many forms, only some of which can be seen or felt, it is defined by its effect on matter. For example, microwave ovens produce energy to cook food, but we cannot see that energy. In contrast, we can see the energy produced by a light bulb when we switch on a https://www.quora.com/How-efficient-is-a-microwave-oven-at-converting- lamp. electrical-energy-into-microwave-radiation-and-then-transferring-the- energy-into-the-food The forms of energy include mechanical energy, thermal energy, radiant energy, electrical energy, nuclear energy, and chemical energy. Introduction to Energy Forms and Units of Energy Mechanical Energy – is energy that results from either the movement or location of an object. Mechanical energy is the sum of kinetic energy and potential energy. e.g. A moving car has kinetic energy. If you move the car up a mountain, it has kinetic and potential energy. A book sitting on a table has potential energy. Introduction to Energy Forms and Units of Energy Kinetic Energy – is the energy of motion EK= ½ mv2 = ½ m (v22 - v12) Potential Energy – is stored energy EP= mg∆h = mg(h2 – h1) Let’s test your knowledge A 2562 g rock is at a height of 280 meters. What is the rock’s gravitational potential energy (in Joules) at 280 meters high? A 3-kg arrow is being released from the bow at a speed of 30 m/s. How much kinetic energy (in BTU) does the arrow have? (1 kg = 2.2 lb, 1 m = 3.28 ft) A box has a mass of 5.8kg. The box is lifted from the garage floor and placed on a shelf. If the box gains 145J of Potential Energy, how high is the shelf ? Introduction to Energy Forms and Units of Energy Thermal Energy – results from atomic and molecular motion; the faster the motion, the greater the thermal energy. The temperature of an object is a measure of its thermal energy content. e.g. A cup of hot coffee has thermal energy. Additionally, you produce heat and possess thermal energy in relation to your surroundings. Introduction to Energy Forms and Units of Energy Radiant Energy – is the energy carried by light, microwaves, and radio waves. e.g. Objects left in bright sunshine or exposed to microwaves become warm because much of the radiant energy they absorb is converted to thermal energy. Introduction to Energy Forms and Units of Energy Electrical Energy – results from the flow of electrically charged particles. e.g. When the ground and a cloud develop a separation of charge, for example, the resulting flow of electrons from one to the other produces lightning, a natural form of electrical energy. Introduction to Energy Forms and Units of Energy Nuclear Energy – is energy resulting from nuclear reactions or changes in the atomic nuclei e.g. Nuclear fission, nuclear fusion, and nuclear decay are examples of nuclear energy. An atomic detonation or power from a nuclear plant are also examples of this type of energy. Introduction to Energy Forms and Units of Energy Chemical Energy – results from chemical reactions between atoms or molecules. There are different types of chemical energy, such as electrochemical energy and chemiluminescence. Introduction to Energy Forms and Units of Energy Energy can be converted from one form to another. Although energy can be converted from one form to another, the total amount of energy in the universe remains constant. This is known as the law of conservation of energy: Energy cannot be created or destroyed. Introduction to Energy Forms and Units of Energy To account properly for all types of energy, two things are important: a. One must specify precisely what is being studied. The system is the part of the universe that is being studied. Everything outside the system is considered the surroundings. The imaginary layer that separates the system and the surroundings is called the boundary. The totality of the three parts is called the universe. Introduction to Energy Forms and Units of Energy To account properly for all types of energy, two things are important: b. Identify the mode and dynamics of energy transfer. The boundary may be a physical container or might be a more abstract separation. But one must be consistent; the same choice of system and surroundings must be used throughout a particular problem. Once an appropriate choice of a system has been made, the concept of conservation of energy immediately becomes useful. Introduction to Energy Forms and Units of Energy The units of energy are the same for all forms of energy. Joule calorie 1 cal = 4.184 J British Thermal Unit (BTU) 1 BTU = 1055 J erg 1 J = 107 ergs electron-volt (eV) 1 J = 6.24 x1018 eV watt-hr 1 w-h = 3600 J barrel-of-oil equivalent 1 bboe = 6.1 GJ cubic-meter-of-natural gas equivalent 1 cmge = 37-39 MJ ton-of-coal equivalent 1 toce = 29 GJ Introduction to Energy Heat and Work: Forms of Energy Transfer Heat and work are two different ways of transferring energy from one system to another. The distinction between Heat and Work is important in the field of thermodynamics. Heat is the transfer of thermal energy between systems, while work is the transfer of mechanical energy between two systems. Introduction to Energy Heat and Work: Forms of Energy Transfer WORK (w) – is the transfer of energy from one mechanical system to another w = F∆d w = F∆d cosØ w = ma∆d Introduction to Energy Heat and Work: Forms of Energy Transfer When two systems reach the same temperature, they HEAT (q) – the transfer of thermal are said to be in a state of thermal equilibrium. energy between molecules within a system. Always flows from high temperature to low temperature. TEMPERATURE – describes the average kinetic energy of molecules within a system https://www.yourdictionary.com/articles/heat-temp-difference Introduction to Energy Heat and Work: Forms of Energy Transfer HEAT (q) transfer mechanisms CONDUCTION – transfer of heat from one molecule to another by direct contact CONVECTION – the process of transferring heat through air or liquid currents RADIATION – transfer of heat due to the emission of electromagnetic waves (or photons) https://sciencenotes.org/heat-transfer-conduction-convection-radiation/ Introduction to Energy Heat and Work: Forms of Energy Transfer During the transfer of energy, energy can be lost by the system but it must be gained by the surroundings. Thus, the heat generated is transferred from the system to its surroundings. This reaction is an example of an exothermic process (-). Meanwhile, when heat has to be supplied to the system by the surroundings, it is called an endothermic process (+). Let’s Test your Knowledge Identify which of the following examples is conduction, convection, or radiation: 1. Heat from the sun warming your face 2. Ironing of clothes 3. Release of alpha particles during the decaying of Uranium-238 into Thorium-234 4. Boiling water inside a kettle 5. Hot air rises and cooler air sinks and replaces it 6. Holding an ice cube with bare hands Introduction to Energy Heat and Work: Forms of Energy Transfer +q +w Sign conventions for WORK (w) and HEAT (q) If heat flows into a system, q is positive. If heat flows out of a system, q is negative. If the surroundings do work on the system, w is positive. System If the system does work, w is negative. -q -w Introduction to Energy Heat and Work: Forms of Energy Transfer In chemistry, we are normally interested in the energy changes associated with the system and by definition, energy is the ability to do work or transfer heat. Therefore, ΔU = q + w + ΔU – net gain of energy (endergonic) - ΔU – net loss of energy (exergonic) Introduction to Energy Heat Capacity and Specific Heat Heat capacity is the quantity of heat required to change the temperature of a system by one degree. Molar Heat Capacity, cn – heat capacity per mole of substance (J/mol-K) q = CΔT Specific Heat Capacity, c – heat capacity per gram of substance (J/g-K) C = mc → q = mcΔT Heat Capacity, C – total heat capacity C = ncn → q = ncnΔT (J/K) Introduction to Energy Heat Capacity and Specific Heat Let’s test your knowledge A 15.0g piece of cadmium metal absorbs 134J of heat while rising from 24.0oC to 62.7oC. Calculate the specific heat of cadmium. How much heat does it take to increase the temperature of a 540.6-g sample of Fe from 20.0 °C to 84.3 °C? The specific heat of iron = 0.450 J/g °C. A flask containing 8.0×102 g of water is heated, and the temperature of the water increases from 21 °C to 85 °C. How much heat did the water absorb? cH2O= 4.184 J/g °C Introduction to Energy Introduction to Calorimetry In chemistry and thermodynamics, calorimetry is the process of measuring the amount of heat released or absorbed during a chemical reaction or physical process. To do so, the heat is exchanged with a calibrated object (calorimeter). A calorimeter is a device used to measure the amount of heat involved in a chemical or physical process. Introduction to Energy Introduction to Calorimetry Introduction to Energy Introduction to Calorimetry Types of Calorimeter 1. Adiabatic Calorimeters 2. Reaction Calorimeters 3. Bomb Calorimeters (Constant Volume Calorimeters) 4. Constant Pressure Calorimeters 5. Differential Scanning Calorimeter Introduction to Energy Introduction to Calorimetry If we place a hot metal in the water, heat will flow from M to W. The temperature of M will decrease, and the temperature of W will increase, until the two substances reach thermal equilibrium. Ideally all of this heat transfer occurs between the two substances, with no heat gained or lost by either its external environment. Introduction to Energy Introduction to Calorimetry – Sample Problem A 360.0-g piece of rebar (a steel rod used for reinforcing concrete) is dropped into 425 mL of water at 24.0 °C. The final temperature of the water was measured as 42.7 °C. Calculate the initial temperature of the piece of rebar. Assume the specific heat of steel is approximately the same as that for iron which is 0.449 J/g °C, and that all heat transfer occurs between the rebar and the water (there is no heat exchange with the surroundings). qrebar = – qwater (mc∆T)rebar = – (mc∆T)water mrebar x crebar x (Tf, rebar – Ti, rebar) = – [mwater x cwater x (Tf, water – Ti, water)] Introduction to Energy **Density of H2O is 1g/mL Introduction to Calorimetry – Sample Problem (mc∆T)rebar = – (mc∆T)water mrebar x crebar x (Tf, rebar – Ti, rebar) = – [mwater x cwater x (Tf, water – Ti, water)] (360.0 g) (0.449 J/g °C)(42.7 °C – Ti, rebar) = – (425.0 g)(4.184 J/g °C)(42.7 °C – 24.0 °C) Ti, rebar = 248 °C Introduction to Energy Introduction to Calorimetry – Exercise A 248-g piece of copper (c=0.385 J/g °C) initially at 314 °C is dropped into 390 mL of water initially at 22.6 °C. Assuming that all heat transfer occurs between the copper and the water, calculate the final temperature. Introduction to Energy Introduction to Calorimetry – Exercise When 50.0 mL of 1.00 M HCl(aq) and 50.0 mL of 1.00 M NaOH(aq), both at 22.0 °C, are added to a coffee cup calorimeter, the temperature of the mixture reaches a maximum of 28.9 °C. What is the approximate amount of heat produced by this reaction? HCl(aq)+NaOH(aq)⟶NaCl(aq)+H2O(l) qrxn = -qsoln Introduction to Energy Introduction to Calorimetry – Exercise When 100 mL of 0.200 M NaCl(aq) and 100 mL of 0.200 M AgNO3(aq), both at 21.9 °C, are mixed in a coffee cup calorimeter, the temperature increases to 23.5 °C as solid AgCl forms. How much heat is produced by this precipitation reaction? What assumptions did you make to determine your value? Introduction to Energy Introduction to Calorimetry – Exercise Bomb Calorimeter When 3.12 g of glucose, C6H12O6, is burned in a bomb calorimeter, the temperature of the calorimeter increases from 23.8 °C to 35.6 °C. The calorimeter contains 775 g of water, and the bomb itself has a heat capacity of 893 J/°C. How much heat was produced by the combustion of the glucose sample? qrxn=−(qwater+qbomb) Get in Touch With Us Send us a message or visit us City of Batac, Ilocos Norte, Philippines (63) 77-600-0459 [email protected] Follow us for updates facebook.com/MMSUofficial www.mmsu.edu.ph