For a spontaneous process:
A pendulum is put in motion, with all of its molecules moving in the same direction
As it moves, the pendulum collides with air molecules.
When it comes to rest, the pendulum has dispersed its energy. This is a spontaneous
Criterion for a Spontaneous Reaction
The criterion is that the entropy of the system and its surroundings must increase.
Third Law of Thermodynamics
A substance that is perfectly crystalline at zero Kelvin (0 K) has an entropy of zero.
The standard entrop
First Law of Thermodynamics; Enthalpy (cont.)
Relate the change of internal energy, DU, and heat of reaction, q.
heat of reaction at constant pressure, qp, equals the change of enthalpy, DH.
Spontaneous Processes and Entropy
Entropy and the S
To fully specify a voltaic cell, it is necessary to give the concentrations of solutions or
ions and the pressures of gases. In the cell notation, these values are written within
parentheses for each species.
For example, the oxidation of Cu(s) to Cu2+(aq
An electrochemical cell is a system consisting of electrodes that dip into an electrolyte
and in which a chemical reaction either uses or generates an electric current.
A voltaic or galvanic cell is an electrochemical cell in which a spontaneous reaction
Free Energy and Equilibrium Constants
Relating DGo to the Equilibrium Constant
thermodynamic equilibrium constant, K.
expression for a thermodynamic equilibrium constant.
freeenergy change of a reaction and the reaction quotient are related.
DG as a Criterion for Spontaneity
The spontaneity of a reaction can now be determined by the sign of DG.
DG < 10 kJ: spontaneous
DG > +10 kJ: nonspontaneous
DG = very small or zero (< +10 kJ and
> 10 kJ): at equilibrium
Interpreting Free Energy
A voltaic cell employs a spontaneous oxidationreduction reaction as a source of
energy. It separates the reaction into two halfreactions, physically separating one
halfreaction from the other.
Our first step in studying electrochemical cell is to balance
Changing the temperature changes the value of the equilibrium constant.
Changing the temperature can also cause a shift in the equilibrium.
The direction of each of these changes depends on the sign of DHo.
For an endothermic reaction, DHo > 0 (positive),
Fe2+(aq) Fe3+(aq) + e
First we balance N, then O:
NO3(aq) NO(aq) + 2H2O(l)
Next we balance H:
4H+(aq) + NO3(aq) NO(g) + 2H2O(l)
Then we balance e:
3e + 4H+(aq) + NO3(aq) NO(aq) + 2H2O(l)
Finally, we combine th
A l i off Q
Ivan Avrutsky, ECE7030, Math Methods in Engineering, Lecture 26, Fall 2007
Fall 2007 ECE 7030 Quiz#2
1. (2.5 pt) In the metric space of real functions f(x) defined over the interval x(- , ) with the metr