1st Law of Thermodynamics
energy of universe is constant
2nd Law of Thermodynamics
process spontaneous in one direction can't be spontaneous in reverse direction
state function
?H, ?S, ?G
energy released
bonds formed; exothermic
energy absorbed
bonds broken; endothermic
?H
H(products)-H(reactants)
heat of formation
?H = ?H(products)-?H(reactants)
heat capacity
heat � ?T
specific heat
q = mc?T OR q = gs?T
Gibbs free energy
measure of spontaneity of process
?G negative
spontaneous
?G positive
not spontaneous
?G = 0
reaction at equilibrium
?G�
?H - T?S
?G
?G� + RT(lnQ)
?G�
8.31 J/mol*K
exothermic reaction
reactants start higher than products
endothermic reaction
reactants start lower than products
entropy
measure of disorder of system
liquids
more disordered than solids
gas
more disordered than liquids
particles
in solution have higher entropy values than solids
liquids
have higher entropy values than solids
gases
have higher entropy values than liquids
2 moles of substance
have higher entropy value than one mole
entropy change ?S
?S�(products) - ?S�(reactants)
standard state conditions
1. all gases are at 1 atm
2. all liquids are pure
3. all solids are pure
4. all solutions are at 1-M
5. the energy of formation of an element in its normal state is defined as 0
6. temperature used for standard state values is almost invariably room tempe
heat of vaporization
energy given off when substance condenses
heat of fusion
energy taken in by substance when melts
addition of catalyst
decreases activation energy only
spontaneous endothermic reaction
?H > 0
?S > 0
spontaneous process
one that proceeds on its own without assistance, they are irreversible unless the surroundings are changed and they can be fast or slow
Exothermic Reactions
negative ?H, favors spontaneity but does not guarantee it.
entropy
defined as a measure of randomness or disorder of a system. S solid< S liquid< S gas
Entropy of a system increases when
gases are formed from solids or liquids, liquids or solutions are formed from solids, the number of gas molecules changes during a chemical reaction
standard entropy
S� is the absolute entropy of a mole of a substance at 1 atm and 35�C. J/Mol K. for all elements and compounds the standard entropy is always positive.
+?S
becomes more random; disordered
-?S
becomes more ordered
calculating ?S for a reaction
?S(rxn)= ?S� products - ?S�reactants
3rd Law of Thermodynamics
the entropy of a pure solid at absolute zero is zero
standard molar entropies of elements and diatomics
are not 0 unlike standard molar enthalpies
standard molar entropies for gases
are greater than those of liquids and solids
standard molar entropies generally increase with ____
increasing molar mass and increasing number of atoms in the formula substance
spontaneous processes due to the 2nd law of thermodynamics
the entropy of the universe increases in a spontaneous process and remains unchanged in a equilibrium process ?S(univ) = ?S(sys) + ?(surr)
Gibbs free energy equation
?G = ?H - T?S
standard free energy
?G�(rxn) is the free energy change of a reaction when it occurs under standard conditions; when reactants in their standard states are converted to products in their standard states.
?G�rx
#NAME?
spontaneous at all temperatures
-?H (favorable)
+?H (favorable)
nonspontaneous at all temperatures
+?H (unfavorable)
-?S (unfavorable)
spontaneous at low T; nonspontaneous at high T
-?H (favorable)
-?S (unfavorable)
spontaneous at high T; non spontaneous at low T
+?H (unfavorable)
+?S (favorable)
-?G
the forward process is spontaneous (the reverse is nonspontaneous)
+?G
the forward process is nonspontaneous (the reverse is spontaneous)
?G=0
the reaction is at equilibrium
what is special about ?G being equal to zero?
one can say that the reaction will become spontaneous either above or below the temp
Equation for finding ?G when ?H, T and ?S are known
?G=?H-T?S
Phase transitions
if the process is melting, the ?H is the same as the heat of fusion. if the process is freezing, the ?H is the negative value of the heat of fusion. if the process is boiling, the ?H is the heat of vaporization. if the process is condensing, the ?H is the
what does Q stand for
reaction quotient: the mass action expression at non-equilibrium conditions. the spontaneity of a reaction that has not reached equilibrium has to be measured in terms of ?G which is not synonomous with ?G� because the substances are not in standard state
Finding ?G when ?G� and Q are known
?G = ?G� + RTlnQ
calculating equilibrium constant if ?G� is known
?G� = -RTlnK(c or p or sp)
Enthalpy (heat) of combustion
the heat released or absorbed (enthalpy change) during the formation of a pure substance from its elements, at constant pressure and usually denoted by ?Hf.
Hess's law
The overall enthalpy change in a reaction is equal to the sum of the enthalpy changes of the individual steps of the process.
Specific Heat
the amount of heat required to raise the temperature of 1g of the substance by 1�C
Exothermic
When ?H is negative. Releases heat.
Endothermic
When ?H is positive. Absorbs heat.
Conductor
material that moves heat energy between two points (good - metal; bad - wood)
Insulator
reduces heat transfer to and from its surroundings
Calorimeter insulated device used for measuring the amount of heat absorbed or released through a chemical or physical process
insulated device used for measuring the amount of heat absorbed or released through a chemical or physical process
bomb calorimeter
sealed, insulated container used for measuring the energy released during combustion
sealed, insulated container used for measuring the energy released during combustion
heating curve
a diagram that shows the temperature changes and changes of state of a substance as it is heated
potential energy diagram
a diagram that shows the changes in potential energy that takes place during a chemical reaction
Molar Heat Capacity
C= J/mol�C The amount of heat required to raise the temp of one mole of a substance by 1�C.