CHM - Chapter 17 Energy Energy The ability to do work or...

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Unformatted text preview: Chapter 17 Energy Energy The ability to do work or cause a change Work-using force to move something Symbol is w Thermochemistry- studies energy changes in reactions q is heat Heat flows from high temperature to low temperature The Universe Can be divided into 2 pieces System- the part you are investigating Surroundings- the rest of the universe Law of conservation of energy- Energy cant be created or destroyed The energy of the universe is constant Energy change of System + Energy change of surroundings = 0 Exothermic System releases energy Heat flows out Surroundings get hotter q is negative System Surroundings Energy Endothermic System absorbs energy Heat flows in Surroundings get cooler q is positive System Surroundings Energy 6 Units of Energy Energy is measured in Joules or calories calorie is amount of heat to change 1 g of water by 1 C Food Calories are kilocalories 1Calorie = 1000 calories 1 cal = 4.184 J 7 Heat capacity How much heat it takes to heat an object by 1 C Affected by two things What the substance is Mass of the object Specific heat is the amount needed to heat 1 g by 1 C Only depends on the substance Table pg 17.1 Pg. 508 8 Heat capacity The higher the specific heat the more energy it takes to change its temperature. Pizza burning the roof of your mouth The same amount of heat is released when an object cools down 9 Heat capacity Equation q = m T C Heat = mass x temp x specific change heat Same as Chapter 15 How much heat is needed to change the temperature of 12 g of silver with a specific heat of 0.057 cal/g C from 25 C to 83 C? If you put 6500 J of heat into a 15 g piece of Al at 25 C , what will the final temperature be? ( C = 0.90 J/g C ) Calorimetry Measuring heat. Use a calorimeter. Two kinds Constant pressure calorimeter (called a coffee cup calorimeter) An insulated cup, full of water. q = m T C For water C is 1 cal/gC Dissolve chemicals, measure temp before and after Calorimetry Enthalpy (H) heat content at constant pressure Coffee cup calorimeter measure how much heat content changes H H = q We will use heat and change in enthalpy interchangeably If temperature goes up exothermic Example...
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CHM - Chapter 17 Energy Energy The ability to do work or...

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