4-Thermodynamics 23-24 .pdf

Physical Pharmacy Thermodynamics Dr.Khalid T Maaroof Thermodynamics  Thermodynamics is about energy, its flow and its transformation from one form into another form. Thermodynamics Control of Chemical Reactions Spontaneity of reaction rate of reaction Forms of energy The INTERNAL ENERGY,...

Physical Pharmacy Thermodynamics Dr.Khalid T Maaroof Thermodynamics  Thermodynamics is about energy, its flow and its transformation from one form into another form. Thermodynamics Control of Chemical Reactions Spontaneity of reaction rate of reaction Forms of energy The INTERNAL ENERGY, E of a system is the sum of the kinetic and potential energies of all the particles that compose the system or the total energy of a system. Some terms:  System: A region of the universe that we direct our attention to.  Surroundings: Everything outside a system is called surroundings. Boundary: The boundary that separates a system from its surroundings.  Thermodynamic systems Thermodynamic systems Energy Transfer: Heat and Work • Energy may enter or be withdrawn from a system as heat or work. Energy Transfer: Heat and Work  Heat is the transfer of thermal energy between two bodies that are at different temperatures  Work is transfer of energy used to change height of a weight of system in respect to surrounding. Work is either be done by the system (-) or on the system (+) System Work (w) Surroundings Heat (q) Heat The transfer of energy as a result of a temperature difference is called heat. Work Thermodynamic state   It is the state of the system with definite value of dependent variable. E.g of State variables are : Pressure, Temperature, and Volume. Thermodynamic process  Change from one equilibrium state to another Zero (law) of thermodynamics  The Zero Law of Thermodynamics states that if two systems are in thermodynamic equilibrium with a third system, the two original systems are in thermal equilibrium with each other. System A System B System C First law of thermodynamics There Is No Free Lunch!!  In universe energy can not be created or destroyed only transformed ΔEuniv=ΔEsys+ΔEsurr=0 ΔEsys=−ΔEsurr   The First Law of Thermodynamics states that energy can be converted from one form to another with the interaction of heat, work and internal energy, but it cannot be created nor destroyed, under any circumstances. ΔE=Q+W 1st law of Thermodynamics is about Conservation of Energy   As heat is applied to a closed system, the system does work by increasing its volume. w=PΔV The sum of heat and work is the change in internal energy, ΔE. In an isolated system, Q=−W. Therefore, ΔE=0. Heat content (enthalpy): Enthalpy is the heat content of a system, or the amount of energy within a substance, both kinetic and potential.  The increase in enthalpy, ∆H, is equal to the heat absorbed by the system at constant pressure. Q = H2 – H1 = ∆H  The first law equation become: ∆H = ∆E + P∆V  Second law of thermodynamics ➢ Second    law of thermodynamics is about spontaneity of processes. Heat does not go from a colder body to a hotter body. flow of heat is always from a hotter body to a colder body. The entropy of the universe will increase during any spontaneous change. Entropy      Entropy is the measure of disorder Is a quantitative measure of increasing the probability of spontaneous process. From statistical mechanics we had seen that ∆S increases during a spontaneous process, so these results give us : ∆ S <0 for non spontaneous processes ∆ S = 0 for a system at equilibrium ∆ S > 0 for spontaneous processes Entropy   The Second Law of Thermodynamics states that the state of entropy of the entire universe, as a closed isolated system, will always increase over time. Entropy in the universe can never be negative. Free energy  ΔG=ΔH−TΔS  ΔH refers to the heat change for a reaction. A positive ΔH means that heat is taken from the environment (endothermic). A negative ΔH means that heat is emitted or given to the environment (exothermic).  ΔG is a measure for the change of a system's free energy.    If ΔG < 0, the process occurs spontaneously. If ΔG = 0, the system is at equilibrium. If ΔG > 0, the process is not spontaneous as written but occurs spontaneously in the reverse direction. ΔG=ΔH−TΔS Case Reaction ΔH ΔS ΔG 1. high temperature - + - Spontaneous 2. low temperature - + - Spontaneous 3. high temperature - - + Nonspontaneous 4. low temperature - - - Spontaneous 5. high temperature + + - Spontaneous 6. low temperature + + + Nonspontaneous 7. high temperature + - + Nonspontaneous 8. low temperature + - + Nonspontaneous Example: O2 2O occurs spontaneously under what temperature conditions? ➢ Answer:  By simply viewing the reaction one can determine that the reaction increases in the number of moles, so the entropy increases.  The enthalpy is positive, because covalent bonds are broken. When covalent bonds are broken energy is absorbed, which means that the enthalpy of the reaction is positive. So, if the temperature is low it is probable that ΔH is more than T∗ΔS, which means the reaction is not spontaneous. If the temperature is large then T∗ΔS will be larger than the enthalpy, which means the reaction is spontaneous. Other examples    Melting Complexation of I2 with KI Polyprotic acids Heat of reaction intra-molecular forces vary in strength because of interplay between attraction and repulsion forces. Therefore, the net bonding energy that holds a series of atoms together in a molecule is the additive result of all the individual bonding energies. The net energy associated with the heat of reaction, can be estimated from the bond energies that are broken and the bond energies that are formed during the reaction process. Example:  Calculate the bond energy (ΔH ) in the following structure when broken. if you know that: C==C bond is broken (requiring 130 kcal), a Cl—Cl bond is broken (requiring 57 kcal), a C—C bond is formed (liberating 80 kcal), and two C—Cl bonds are formed (156 kcal). Δ H = 130 + 57 - 80 -156 = -49 kcal 1 cal = 4.184 joules, -49 kcal is expressed as -205.016 joules. Questions !