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# CHEM 126 Chapter 6

### CHEM 126 Final

heat energy transferred between system & surroundings due to difference in temp (thermal) - thermal energy of molecule motion - Q
work - energy transferred when object is moved by force - W
relationship between change in energy, heat, work - ∆E = q + w
- Q > 0 - E increases
heat FROM system TO surroundings - q < 0 - E decreases
work done ON system BY surroundings - w > 0 - E increases
work done BY system ON surroundings - w < 0 - E decreases
E increases when.. - Q > 0 - W > 0
E decreases when... - Q < 0 - W < 0
P-V work - W = -P * ∆V - use when rxn occurs that changes V of system - undergoes V change by pushing against surroundings -> do work
units of energy - E = (1/2)M*V^2 * mass = kg & volume = m/s - 1 joule = 1 kg*m^2/s^2 - 1 caolire = 4.184 J
state function - values depeond only on the state that the system is in, not path it took to get there - EX: altitude, energy, enthalpy, pressure, volume, temp
change of enthalpy in terms of change of internal energy/heat ∆E = q - P∆V - at constant P (qp) = ∆E + P∆V ***** ∆H = ∆E + P∆V = qp (P∆V is usually 0)
endothermic vs. exothermic ∆H > 0: endothermic - absorb heat ∆H < 0: exothermic - release heat
specific heat capacity - amount of heat required to change the temp of 1 gram of a material by 1 degree Kalvin - Q = C * M * ∆T - C = J/(g*K), M = grams, T = Kelvin, Q = Joules
constant pressure - coffee cup calorimeter - qp = ∆H
constant volume - bomb calorimeter - qv = ∆E (used for combustion)
constant pressure calometry equation -T final water = T final solid - q H20 = - q solid - C H20 * M H20 * ∆T H20 = -(C solid * M solid * ∆T solid)
Hess's law - ∆H rxn = sum of the enthalpy changes for the individual steps ** make sure excess elements cross off, moles match up, reverse sign if rxn needs to be reveresed
stand heats of rxn & standard heats of formation - ∆H rxn° = ∆H rxn under standard conditions - ∆H f° = enthalpy change for the formation of 1 mol of substance from its elements in their standard state
hess's law + heat of formation ∑(number of mols * heat of rxn(products)) - ∑(number of mols*heat of reaction(reactants))
Created by: ccottrel