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31 Cards in this Set
- Front
- Back
Energy
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Ability to do work
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Work
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To move an object against an opposing force
Ordered transfer of energy |
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Heat
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Mode of energy transfer which occurs as a result of a temp difference an produces an increase in disorder in how the particles behave
Increases the average kinetic energy of a the molecules in a disordered fashion |
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Open system
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Can exchange energy and matter with the surroundings
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Closed system
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Can exchange energy but not matter with the surroundings
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Heat in a system can be
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Transferred but the total energy of system and surroundings cannot be changed
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Enthalpy
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Measure of the amount of heat energy contained in a substance
Heat content of a system Stored in the chemical bonds and intermolecular forces as potential energy |
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Positive H
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Heat is added to the system
Endothermic Less common |
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Negative H
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Heat is released from the system to the surroundings
exothermic Most combustion and all neutralization Products more stable than reactants |
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energy cycle
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Either the elements form the reactants which then react to form products or the elements burn separately
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Hess' Law
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H1 +H2 = H3
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see notes to how to use Hess' Law
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standard enthalpy changes
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Measured under 298K and 1.00x10^5 Pa
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standard enthalpy change of formation
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The enthalpy change that occurs when one mole of the substance is formed from its elements in their standard states
Gives measure of the stability of a substance relative to its elements Can be used to calculate the enthalpy changes of all reactions Can have fractions See notes |
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formula for standard enthalpy changes of formation
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H reaction = Sum of H products - Some of H reactants
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bond enthalpy
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Energy needed to break one mole of bonds in gaseous molecules under standard conditions
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average bond enthalpies
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Used to compare bond enthalpies which exist in different environments
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breaking bonds
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Endothermic (when bonds broken are stronger than bonds made), involves the separation of particles which are held together by a force of attraction
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making bonds
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Exothermic (when bonds made are stronger than bonds broken), involves the bringing together of particles which have an attractive force between them
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Bond enthalpy equation
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H reaction= sum of H products-Sum of H reactants
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oxygen comes in what forms
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O2 and O3
Ozone protects us from UV |
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bonds in oxygen and ozone are broken when
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They absorb UV radiation in sufficient energy
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energy needed to break O2 in comparison to O3
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O2 is stronger so its broken by radiation of higher energy and shorter wavelengths
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energy of a photon
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Hxv (frequency) or hxc/y(wavelength)
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temp of atmosphere
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Usually decreases with height but at 12 km, temp begins to rise because of UV radiation
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in stratosphere
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Strong covalent double bond in normal oxygen O2 is broken by high-energy UV radiation with a wavelength shorter than 242 nm to form 2 oxygen atoms
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free radicals
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Species with unpaired electron
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free radicals of oxygen react with another oxygen molecule to form
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Ozone
Exothermic because it raises temp of stratosphere |
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UV wavelength to break ozone
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<330nm
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free radicals of oxygen react with
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another ozone atom to form 2 oxygen moleculesExothermic, maintains high temp of stratosphere |
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steady state
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Level of ozone stays as a constant level if rate of formation is balanced by rate of removal
Described by Chapman Cycle |