Chapter 6 - 1 ENERGY AND ITS DIFFERENT FORMS What is Energy...

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1 ENERGY AND ITS DIFFERENT FORMS What is Energy - good question! - capacity to do work or to supply heat - best to learn what is energy through examples Kinetic and Potential Energy Kinetic Energy - energy of movement - K.E. = ½mv 2 m – mass v – velocity - examples - baseball moving - thermal energy (molecules moving) Potential Energy - energy stored that is released through motion - ball in air - battery - electrical energy is stored in battery - electrons start moving when circuit is made - thus electrical energy is released - chemical energy - Potential chemical energy of wood is changed into kinetic energy when it is burned. - Explosives have a large amount of potential energy. TYPES OF ENERGY Light Energy – as in energy from a light bulb Heat Energy – as in energy from a fire Electrical Energy – as in putting your finger in an electrical socket Ouch! Mechanical Energy – as in energy from an engine or water wheel Chemical Energy – as in energy from burning gasoline (chemical energy is converted to heat and light) - Chemical energy is stored inside a substance until a substance undergoes a chemical change. Then it can released or sometimes absorbed. **- Chemical energy is stored in chemical bonds between atoms.** h Potential energy depends on distance from earth’s surface.
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2 Energy exchange in chemical reactions Exothermic - energy is released when reaction occurs - most reactions are exothermic Endothermic - energy is absorbed when reaction occurs - example is an instant cold pack. Potential energy can be converted to kinetic energy. - ball falling - log burning - discharging battery Kinetic energy can be converted to potential energy - lifting box - charging battery - electricity is generated by motion - waterfall, windmill, steam turbine, etc… Definition: Internal Energy is the sum of kinetic and potential energy in a thermodynamic system. STATE FUNCTIONS A State Function is a thermodynamic quantity whose value depends only on the state at the moment, i. e., the temperature, pressure, volume, etc… The value of a state function is independent of the history of the system. Internal energy is an example of a state function. The fact that internal energy is a state function is extremely useful because it we can measure the energy change in the system by knowing the initial energy and the final energy. In other words, we don’t need all of the nitty-gritty detail of a process to measure the change in the value of a state function. In contrast, we do need all of the nitty-gritty details to measure the heat or the work of a system.
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3 ENERGY UNITS Joule - = defined as J kg m s 1 1 2 2 - = = K E mv kg m s kg m s . . 1 2 2 2 2 2 2 - SI unit (our preferred unit) Calorie - 1 cal = 4.184 J (exact) (new definition of cal.) - old definition of calorie: energy needed to raise the temperature of 1 g of H 2 O 1 ° C - aside: 1 dietary calorie = 1 Cal = 1 kcal *Study of thermodynamic process is divided into two portions.* - system - surroundings - read book for clearer explanation HEAT AND WORK Two ways to classify conversion of potential energy to kinetic energy.
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Chapter 6 - 1 ENERGY AND ITS DIFFERENT FORMS What is Energy...

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