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393157
Thermodynamics Unit
Description
Thermodynamics in AP Chemistry
No tags specified
ap chemistry
ap level
chemistry
Mind Map by
Rachel Todd
, updated more than 1 year ago
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Created by
Rachel Todd
almost 11 years ago
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Resource summary
Thermodynamics Unit
Energy
Can be TRANSFERED
HEAT
Change in system's energy ΔE = q + W
System
ex) a solution of HCL and another of NaOH were mixed together in a beaker with a stir rod
Solution Chem: only the HCl and NaOH melecules (H+, OH-)
Surrounds
EVERYTHING ELSE
What Causes Chemical Rxns?
Free Energy ("nature of reactants")
ΔG = ΔH - TΔS
ΔG: the max amount of energy that can be used to do work
ΔH: energy transferred as heat
TΔS: energy used to create disorder
- : thermodynamically favoured (spontaneous)
+ : NOT thermodynamically favoured
Calculate
#1: Calculate ΔH from calorimtry OR Hess's OR ΔHf; then calculate ΔS using entropy values; and then plug in to find ΔG at a certain temp
#2: Calculate ΔG using ΔGfº values
(ΔG = ΣnΔGº (products)−ΣnΔGº (reactants))
Entropy Δs: measure of disorder *more random wanted*
2nd law: Entropy of Universe is always increasing
ΔS = S(products) - S(reactants)
ΔSrxn = ΣnSº(products) - ΣnSº(reactants)
Positive value is WANTED
Enthalpy
1st Law of Thermodynamics: cannot be created or destroyed
EXO
ΔH = q = -
ENDO
ΔH = q = +
can be calculated 4 ways
#3 Hess's Law
if a rxn is carried in 1 or several steps, the overall change in enthalpy is equal to the sum of the enthalpy changes for each step
#2 Calorimeter
Heat transfer cannot be directly measured
Heat Capacity [kJ/K (or Cº)]
Specific heat capacity: amount of heat needed to raise the temperature of 1 kg of a substance by 1 k [kJ/kg•K (or Cº)]
ΔH rxn vs Δq rxn [ΔH = Δq/n]
total amount of heat lost or gained by a rxn
Using stoichiometry
#1 Bond of Enthalpies
Break bonds NEED energy
For the image: A + B need energy to break up; C + D release energy when formed
Form bonds REALEASE energy
ΔH = ΣnBE - ΣnBE
Σ = sum
n = # of moles
BE = bond energy *from exp't* values must be given
#4 Enthalpy of Formation
An arbitrary value that indicates how much heat would be lost/gained from experimental states
ΔHº rxn=ΣnΔHºf (products)−ΣnΔHºf (Reactants)
n: mol
Most "Hº"'s will be given
q (+): heat transferred IN
q (-): heat transferred OUT
w (+): work done ON the system
w (-): work done BY the system
ΔE is change in PE and KE of particles in a system
WORK W = -PΔV
PE
KE
Temperature
Conversions
C = K - 273
C = (5/9)(Fº - 32)
a measure of the average KE of particles in a system
If KE doubles, the temp doubles as well
CANNOT BE CREATED OR DESTROYED
Media attachments
practice_3-2.gif (image/gif)
Screen_Shot_2013-12-06_at_4.03.04_PM (image/png)
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