Chapter 07 - Energy and Thermochemistry Matter Energy...

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7bff8c027c10ab1fd14bcb3b59314893d7d1bcda.doc Energy and Thermochemistry Matter  Energy fundamental domain of chemistry Up to now, we have been looking at chemical reactions only from the perspective of Matter (ie atoms, molecules). Now we turn our attention to the Energy associated with chemical reactions. Chemical reactions almost all involve a change in energy (usually in the form of HEAT ) Key question; How do we designate a change in Energy ? Can we predict /know how much energy or heat is involved in a chemical reaction Chapter 7 provides answers to both! Thermochemistry study of the energies given off or absorbed by chemical reactions Key learning objective for this chapter understand energy associated with chemical reactions using two techniques; 1. experimental techniques, and related mathematical relationships to determine energy absorbed or given off by a chemical reaction, 2. estimation of energy associated with chemical reactions Review of Kinetic and Potential Energy Kinetic Energy energy of motion Chem 111 Lecture notes By Alan Zombeck page1
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7bff8c027c10ab1fd14bcb3b59314893d7d1bcda.doc Potential Energy “stored” energy Examples of changing the height of an object or compression of a spring Both are related (i.e. you change one, the other changes) by the following equation TOTAL ENERGY = KE + PE Which is the law of the conservation of energy energy can be neither created or destroyed, but can only change forms But how does KE and PE apply to chemistry and chemical reactions? Chemical bond result of a combination of attractive and repulsive Forces represents potential energy Kinetic Theory of Matter Atoms/molecules are always in motion molecular kinetic energy Physical evidence of molecular motion Perfumes, dissolving sugar in hot water, breaking the sound barrier Temperature average kinetic energy Temperature changes signal an energy change ( heat change ) Molecules slow down as temperature decreases; we say that the average kinetic energy decreases Kinetic theory is important because it explains the transfer of heat Chem 111 Lecture notes By Alan Zombeck page2
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7bff8c027c10ab1fd14bcb3b59314893d7d1bcda.doc Examples; hot drink in a cup “Cold” tile floor vs carpet? SI unit of energy is the joule Joule = amount of kinetic energy possessed by a 2 kg object moving at a speed of 1 meter per second using these values in the kinetic energy equation KE = ½ mass · (velocity) 2 Joule = 1 kg·m 2 s -2 Calorie (cal) = energy needed to the temperature of 1 gram of water 1 ° C relationship between Joule and calories 1 cal = 4.184 J (exactly) what about food Calories?
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Chapter 07 - Energy and Thermochemistry Matter Energy...

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