Spontaneity, entropy and free energy
Introduction
- 2 important questions chemists ask when studying chem
rxns:
1. How fast is rxn?
- ie: activation energy in kinetics
2. How far does it proceed
- related to equilibrium. If k is large, goes far. If small,
not very small
Spontaneity
-fundamental goal of thermodynamics is to predict whether a
process/reaction will occur
- ie: will water decompose into hydrogen and oxygen?
- spontaneous process: A process is called spontaneous if it
will occur without ongoing outside intervention
-if conditions are right, it proceeds on its own
-once started, no action from outside the system is
necessary to make process continue when
these
I
deciaces,
S
Examples of spontaneous processes Forenthalpt favoRS
- propane burns when ignited spontanet)
- once ignited the rxn keeps going without further
intervention
- water freezes at temp at 0 Celsius *exotheRmK
- ice melts at room temp -
endotheRMIL
- dissolving of table salt in water at room temp endotheRm(c
-
A favoring spontaneity doesn't guarantee ita
Spontaneous vs no spontaneous process
- spontaneous events occur by themselves w/o ongoing
outside help when conditions are right
- a non spontaneous process will not occurs unless some
external action is continuously applied
, - under given set of conditions, if a process is spontaneous
in one direction, not spontaneous in the other
- nonspontaneous process can be made by coupling it to
another process that’s spontaneous, or by supplying
energy from external source
- spontaneity doesnt tell speed of the process
Factors that influence spontaneity
- the change in enthalpy of the system
- refer to first 2 examples of spontaneous process listed
earlier. What do they have in common?
- decrease in enthalpy
- decrease in enthalpy = spontaneity favored
- second factor for spontaneous change is natures
tendency to move to a condition of maximum disorder
the change in entropy of the system
Introduction
- 2 important questions chemists ask when studying chem
rxns:
1. How fast is rxn?
- ie: activation energy in kinetics
2. How far does it proceed
- related to equilibrium. If k is large, goes far. If small,
not very small
Spontaneity
-fundamental goal of thermodynamics is to predict whether a
process/reaction will occur
- ie: will water decompose into hydrogen and oxygen?
- spontaneous process: A process is called spontaneous if it
will occur without ongoing outside intervention
-if conditions are right, it proceeds on its own
-once started, no action from outside the system is
necessary to make process continue when
these
I
deciaces,
S
Examples of spontaneous processes Forenthalpt favoRS
- propane burns when ignited spontanet)
- once ignited the rxn keeps going without further
intervention
- water freezes at temp at 0 Celsius *exotheRmK
- ice melts at room temp -
endotheRMIL
- dissolving of table salt in water at room temp endotheRm(c
-
A favoring spontaneity doesn't guarantee ita
Spontaneous vs no spontaneous process
- spontaneous events occur by themselves w/o ongoing
outside help when conditions are right
- a non spontaneous process will not occurs unless some
external action is continuously applied
, - under given set of conditions, if a process is spontaneous
in one direction, not spontaneous in the other
- nonspontaneous process can be made by coupling it to
another process that’s spontaneous, or by supplying
energy from external source
- spontaneity doesnt tell speed of the process
Factors that influence spontaneity
- the change in enthalpy of the system
- refer to first 2 examples of spontaneous process listed
earlier. What do they have in common?
- decrease in enthalpy
- decrease in enthalpy = spontaneity favored
- second factor for spontaneous change is natures
tendency to move to a condition of maximum disorder
the change in entropy of the system
