surroundings. system. universe. thermodynamic state of a system. The number of moles and identity of each substance. The physical states of each substance. The temperature of the system. The pressure of the system. Thermochemical standard state conditions The thermochemical standard T = 298.15 K. The thermochemical standard P = 1.0000 atm. Be careful not to confuse these values with STP. Thermochemical standard states of matter For pure substances in their liquid or solid phase the standard state is the pure liquid or solid. For gases the standard state is the gas at 1.00 atm of pressure. For gaseous mixtures the partial pressure must be 1.00 atm. For aqueous solutions the standard state is 1.00 M concentration. State Functions are independent of pathway: T (temperature), P (pressure), V (volume), E (change in energy), H (change in enthalpy the transfer of heat), and S (entropy) Examples of non-state functions are: n (moles), q (heat), w (work)
There are two basic ideas of importance for thermodynamic systems Law of Conservation of mass and the Law of Conservation of Energy. The second leads to 3 thermodynamic laws. First Law the energy of the Universe is constant Chemical systems tend toward a state of minimum potential energy. The first law is also known as the Law of Conservation of Energy. Energy is neither created nor destroyed in chemical reactions and physical changes. Esys +Esurr = Euniverse Esys = KEsys + PEsys 1. KE kinetic energy: translational, rotational, vibrational 2. PE energy stored in bonds The second law of thermodynamics states, "In spontaneous changes the universe tends towards a state of greater disorder." Chemical systems tend toward a state of maximum disorder. The entropy of universe must increase. Fundamentally, the system must be capable of doing useful work on surroundings for a spontaneous process to occur. In general for a substance in its three states of matter: Sgas > Sliquid > Ssolid When: S > 0 disorder increases (which favors spontaneity). S < 0 disorder decreases (does not favor spontaneity). The Third Law of Thermodynamics states, "The entropy of a pure, perfect, crystalline solid at 0 K is zero." o o o o o o
S298
nSproducts
nSreactants
n
H 298
nH reactants
n
n
n
n
Go products
nH 298
nG o products
n
nG o reactants
G = H-T S
at constant T and P
The relationship describes the spontaneity of a system. The relationship is a new state function, G, the Gibbs Free Energy. Sign conventions for G. G > 0 reaction is nonspontaneous G = 0 system is at equilibrium G < 0 reaction is spontaneous
heat transfer in (endothermic), +q heat transfer out (exothermic), -q
w transfer in (+w) Compression of system
SYSTEM E = q + w
w transfer out (-w) Expansion of system
Free energy has the relationship G = H -T S. Because 0 H 0 and 0 S 0, there are four possibilities for G.
Forward reaction
H <0 <0 >0 >0
S >0 <0 >0 <0
G <0 T dependent T dependent >0
spontaneity at all T's. at low T's. at high T's. Nonspontaneous at all T's.
mass of solute % w/w = mass of solution
100%
moles of solute M= Liters of solution
m moles of solute kg of solvent
Molality is a concentration unit based on the number of moles of solute per kilogram of solvent.
Mole fraction
XA
number of moles of A number of moles of A + number of moles of B
Colligative properties are properties of solutions that depend solely on the number of particles dissolved in the solution. Colligative properties do not depend on the kinds of particles dissolved. Colligative properties are a physical property of solutions.
1.
2.
3.
4.
There are four common types of colligative properties: Vapor pressure lowering Freezing point depression Boiling point elevation Osmotic pressure Vapor pressure lowering is the key to all four of the colligative properties.
Addition of a nonvolatile solute to a solution lowers the vapor pressure of the solution. The effect is simply due to fewer solvent molecules at the solution's surface. X would 1 - X be occupied by solvent. The solute molecules occupy some of the spaces thatsolute normallysolvent Raoult's Law models this effect in ideal solutions. 0
Psolvent X solute Psolvent
Boiling Point Elevation which Fractional Distillation Freezing Point Depression
is Raoult' s Law
Tf
Osmotic Pressure
K f mi
Tb
K b mi
MRT where: = osmotic pressure in atm L atm mol K T = absolute temperature M = molar concentration of solution R = 0.0821