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Thermochemistry. Thermochemistry. C.11A Understand energy and its forms, including kinetic, potential, chemical, and thermal energies. Supporting Standard. http://www.teachertube.com/viewVideo.php?video_id=127807. Thermochemistry.
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Thermochemistry • C.11A Understand energy and its forms, including kinetic, potential, chemical, and thermal • energies. • Supporting Standard http://www.teachertube.com/viewVideo.php?video_id=127807
Thermochemistry • C.11B Understand the law of conservation of energy and the processes of heat transfer. • Supporting Standard • C.11C Use thermochemical equations to calculate energy changes that occur in chemical • reactions and classify reactions as exothermic or endothermic. • Readiness Standard
Thermochemistry • C.11D Perform calculations involving heat, mass, temperature change, and specific heat. • Supporting Standard • C.11E Use calorimetry to calculate the heat of a chemical process. • Supporting Standard
Vocabulary of Instruction: • energy • kinetic energy • potential energy • thermal energy • specific heat • law of conservation of energy • phase change • heat transfer • calorimetry
Key Understandings and Guiding Questions: • Energy is conserved when heat is transferred. • What is the law of conservation of energy? • What is the difference between heat and temperature? • What are the three types of energy transfer? • List the forms of energy you know about. What is an example for each? • How is a calorimeter used to measure energy transfer?
Energy • Energy is the capacity to do work. • Work is defined as force moving through a distance. • In chemistry we consider the gas pressure against a piston moving it upward as work. • Energy in motion is called ____. • This refers to atoms and molecules moving in gases, liquids, and solids. • What is the other type of energy?
Forms of Energy • Light/Heat(Thermal)---Radiant-from electromagnetic waves • Electricity-from flow of electric charges • Magnetism-from alignment of charged particles which causes attractions or repulsions • Mechanical-from movement of objects • Chemical-energy stored in bonds • Nuclear-energy stored in the nucleus • Sound-from vibrations
Energy • We cannot see energy, only its effects. • Heat is the measure of the total amount of kinetic energy in a system. • It is measured in joules or calories. • It is measured with a calorimeter.
Energy • Temperature is a measure of the effects of heat. It measures the average kinetic energy of a system. • It is measured in oC or K. • It is measured with a thermometer.
Energy • Consider two beakers of water. • One has 100 g of water at 80oC. • One has 100 g of water at 20oC. • Which one has more mass? • Which one has more energy? • Which one has the greater kinetic energy? • What will happen if we pour the two together into a third beaker?
Energy • What will be the mass of the water in the third beaker? • What will be the temperature of the water in the third beaker? • Did the cooler water cool the warm water or did the warmer water warm the cool water? In other words, which way did the heat flow?
Heat Flow • Energy flows from a warmer object to a cooler one, never the reverse. • There really isn’t such a thing as cold; there is just a lack of heat. • The heat of a closed system is maintained (not lost to surroundings). • In fact, those are the only two parts to the universe---systems and surroundings. • If energy is lost by the system, it is gained by the surroundings and vice versa.
Methods of Heat Transfer • Convection • Conduction • Radiation
Law of Conservation of Energy • Energy is never lost or gained, only transferred or transformed. • Heat lost = Heat gained • q = m x C x ∆t where q is in joules or calories, m is in grams, C is the specific heat, and t is in Celsius.
Hess’ Law of Constant Heat Summation • The sum of the heats of formation of the products minus the sum of the heats of formation of the reactants equals the heat of reaction. • The heat of formation is the amount of energy needed to make a compound from its elements.
Gibb’s Free Energy • Gibb’s free energy tells the amount of useful work that can be done by a system. • Because it is work done by a system, it is going out of the system and so is given a negative sign if the reaction is spontaneous. • ∆G = ∆H-T∆S where G is Gibb’s free energy, H is the enthalpy of reaction and S is the entropy of the reaction. T is in Kelvins.
Gibb’s Free Energy • Entropy is the randomness of a system. • More randomness is better. • Gases are more random than liquids which are more random than solids.
