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31 Cards in this Set

  • Front
  • Back
Energy
Ability to do work
Work
To move an object against an opposing force
Ordered transfer of energy
Heat
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
Open system
Can exchange energy and matter with the surroundings
Closed system
Can exchange energy but not matter with the surroundings
Heat in a system can be
Transferred but the total energy of system and surroundings cannot be changed
Enthalpy
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
Positive H
Heat is added to the system
Endothermic
Less common
Negative H
Heat is released from the system to the surroundings
exothermic
Most combustion and all neutralization
Products more stable than reactants
energy cycle
Either the elements form the reactants which then react to form products or the elements burn separately
Hess' Law
H1 +H2 = H3
see notes to how to use Hess' Law

standard enthalpy changes
Measured under 298K and 1.00x10^5 Pa
standard enthalpy change of formation
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
formula for standard enthalpy changes of formation
H reaction = Sum of H products - Some of H reactants
bond enthalpy
Energy needed to break one mole of bonds in gaseous molecules under standard conditions
average bond enthalpies
Used to compare bond enthalpies which exist in different environments
breaking bonds
Endothermic (when bonds broken are stronger than bonds made), involves the separation of particles which are held together by a force of attraction
making bonds
Exothermic (when bonds made are stronger than bonds broken), involves the bringing together of particles which have an attractive force between them
Bond enthalpy equation
H reaction= sum of H products-Sum of H reactants
oxygen comes in what forms
O2 and O3
Ozone protects us from UV



bonds in oxygen and ozone are broken when
They absorb UV radiation in sufficient energy
energy needed to break O2 in comparison to O3
O2 is stronger so its broken by radiation of higher energy and shorter wavelengths
energy of a photon
Hxv (frequency) or hxc/y(wavelength)
temp of atmosphere
Usually decreases with height but at 12 km, temp begins to rise because of UV radiation
in stratosphere
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
free radicals
Species with unpaired electron
free radicals of oxygen react with another oxygen molecule to form
Ozone
Exothermic because it raises temp of stratosphere
UV wavelength to break ozone
<330nm
free radicals of oxygen react with

another ozone atom to form 2 oxygen moleculesExothermic, maintains high temp of stratosphere

steady state
Level of ozone stays as a constant level if rate of formation is balanced by rate of removal
Described by Chapman Cycle