6 - Energy and Chemical Reactions

6 - Energy and Chemical Reactions - Chapter 6 Energy and...

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Chapter 6: Energy and Chemical Reactions Chemical reactions involve transfers of energy Work and heat refer to quantity of energy transferred from one object or sample to another by working or heating processes Working and heating processes transfer energy from one form or one place to another Thermodynamics is the science of heat, work, and transformations of one to the other 6.1 The Nature of Energy Energy (E) is the capacity to do work Kinetic Energy is energy that something has because it is moving o Mechanical Energy is energy of motion of a macroscale object o Thermal Energy is energy of motion of nanoscale objects o Electrical Energy is energy of motion of electrons through an electrical conductor o E k = ½ mv 2 ; m = mass, v = velocity of moving object Potential Energy is energy that something has as a result of its position and some force that is capable of changing that position o Gravitational Energy is energy that an object has because the force of gravity attracts it towards floor; E p = mgh ; m = mass, g = gravitational constant = 9.8 m/s 2 , h = height above surface o Electrostatic Energy is energy that charged particles have because they attract or repel each other o Chemical Potential Energy is energy resulting attractions and repulsions among electrons and atomic nuclei in molecules; type of energy stored in foods and fuels o Calculated in different ways depending on type Potential energy can be converted to kinetic energy and vice versa Energy Units o Joule (J) is SI unit of energy, 1 J = 1 kg m 2 /s 2 ; small unit of energy so kilojoule (kJ) usually used o calorie (cal) = 4.184 J; quantity of energy required to raise temperature of one gram of water by one degree Celsius; kilocalorie = kcal = Calorie 6.2 Conservation of Energy Law of conservation of energy – energy can neither be created nor destroyed—the total energy of the universe is constant; also known as first law of thermodynamics Energy and Working o Doing work or working on an object is a process that transfers energy to an object Energy, Temperature, and Heating o All matter consists of nanoscale particles that are in constant motion and thus has thermal energy o For a given sample, quantity of thermal energy is greater the higher the temperature is o Transferring energy to a sample of matter usually results in a temperature increase that can be measured with a thermometer o Heat or heating refers to energy transfer process that happens whenever two samples of matter at different temperatures are brought into contact; energy always transfers from hotter to cooler sample until both are at the same temperature o Thermal equilibrium is reached when the two objects initially at two different temperatures has reached a common temperature through heat transfer o “Heat transfer” is the transfer of energy by heating and cooling System, Surroundings, and Internal Energy o System – region of primary concern, can have an actual physical boundary or indistinct one; for
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6 - Energy and Chemical Reactions - Chapter 6 Energy and...

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