Energy and Heat Curves Chapter 6 part 1 6.1-6.3
Thermodynamics No work work The science of heat and work Energy is the “ability to do work” or supply heat No work Energy makes things happen Can’t see energy or directly measure energy All chemical reactions (rx) involve energy changes Energy is released or absorbed depending on the balance between the bonds broken/formed Energy is absorbed to break bonds Energy is released to form bonds work
Forms of Energy Potential - stored energy Gravitational - due to position Chemical - energy stored in bonds Electrostatic - b/w + and - ions
Forms of Energy KINETIC ENERGY Energy due to motion Thermal - molecular motion Mechanical - an object’s motion Electrical Sound
Units of Energy calorie or cal Joule or J 1 cal = 4.184 J
First Law of Thermodynamics Conservation of Energy Energy cannot be created nor destroyed; it just changes form
How we look at reactions System - substances undergoing a change Surroundings - everything else not part of system
Heat, q Transfer of thermal energy b/w the system & surroundings from high to low temps
Exothermic and Endothermic Heat is absorbed by a substance Sign: positive Heat is released from a substance Sign: negative Overall energy is conserved!
Calorimetry The study of heat transfer b/w system and surroundings Heat Curve for a Substance T (°C) Occurs for any substance As energy is added a substance warms up, or melts/vaporizes As energy is removed (cooling curve) from a substance it cools down, freezes/condenses Heat transfer depends on 1) mass (m); g 2) size of T change (∆T); 3) Specific heat of material (C); J/ g K Heat added
Heat Curves During a temp change the kinetic energy of a substance increases/decreases q = mC∆T During a phase change the potential energy of a substance increases/decreases
Phase Changes Heat of fusion or ∆Hfus q supplied (+) for s --> l q released (-) for l --> s Heat of vaporization or ∆Hvap q supplied (+) for l --> g q released (-) for g --> l Use ∆Hfus and ∆Hvap as conversions
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