Thermodynamics

1. System - So the system is the particular part of the universe you are interested in studying. 2. Surroundings - The surroundings is the rest of the universe - everything that is outside of the system of inquiry. 3. Universe - The universe is the system and surroundings combined 4. Close system - only allows the exchange or transfer of energy, but not the mass. 5. Open system - An open system is a system which continuously interacts with its environment. 6. Isolated system - is a physical system that does not interact with its surroundings. 7. Potential Energy - The engergy possessed by an object by virtue of its position. 8. Kinetic Energy - The energy that results from motion. The different types of kinetic energy are heat, light, sound, mechanical, and radiant energy. 9. Translational - movement from one point to another (mostly with gases) 10. Vibrational - movement back & forth through a 3-D space ( all states) 11. Rotational - movement around the molecules axis (gases & liquids) 12. Microstates (number of possible rearrangements ; W) - is a specific microscopic configuration of a thermodynamic system that the system may occupy with a certain probability in the course of its thermal fluctuations. (Delete after you answer: is there any relationship between microstates and entropy?) 13. Enthalpy, H= U + PV; Where U is the internal energy of the system and P and V are the pressure and volume of the system, respectively.
 * Objective 1. Be able to define the following terms/concepts: **

14. Entropy, S - is a thermodynamic property that is a measure of the energy not available for useful work in a thermodynamic process. If entropy is positive then there is more disorder. If entropy is negative, there is less disorder. Entropy is measured in J/mol. General Tendencies of entropy: a. Entropy increases from solids to liquids to gases. b. Entropy increases with molar mass. c. Entropy increases as the number of atoms in the formula increase. d. Entropy increases during chemical reactions when there are more moles of products than moles of reactants. This typically is more important than the change in atoms or change in molar mass.

Factors in which effect entropy: a. Physical State b. Temperature c. Number of molecules d. Number of atoms e. Molecular weight f. Change of atom If the ion charge is less than 2, there is an increase in entropy. If the ion charge is greater than 2 there is a decrease in entropy.

15. Endothermic Reactions - A process that absorbs heat. The reaction gets colder. Delta H is positive. Also, the energy of the product of an endothermic reaction is higher than the energy of the reactants. A + B + Energy --> C Involves the breaking of bonds.

16. Exothermic Reactions - A process that gives off heat. The reaction gets hotter. Delta H is negative. The energy of the products of an exothermic reaction is lower than the energy of the reactants. A + B --> C + Energy Involves forming bonds.

17. Heat of formation, Hf - The amount of energy gained or lost when one mole of the substance is formed from its elements under STP.

18. Gibbs Free Energy, G - The energy available to do work .......To calculate : Enthalpy - (Temperature x Entropy) If there is a decrease in gibbs free energy, entropy increases. In other words, the less energy the reaction needs to work, the more entropy produced and vice versa. Gibbs free energy is measured in Kj/mol and can be also found by the sum of the reactants subtracted from the sum of the products.

19. Spontaneity - The likelihood of a reaction to proceed without outside intervention. Outside intervention such as the addition of a catalyst or heat/energy. example: Heat flow from a hot object to a cold one.

20. Standard Conditions - Set conditions that include: solutions have concentrations other than 1M and gases usually have pressure at 1 atm.

First law: energy can be converted from one form to another but cannot be created or destroyed. It is very difficult to determine total energy content of even a small sample. Energy is a state function the first law can be demonstrated measuring the change in energy between initial state and final state.
 * Objective 2: Define and apply the first, second and third law of thermodynamics. **

Second law: The entropy of the universe increases in a spontaneous process and remains unchanged in an equilibrium process. Therefore, the system may undergo a decrease in entropy, as long as the surroundings undergoes a larger increase in entropy, and vice versa. An equilibrium process is one that does not occur spontaneously in either the net forward or net reverse direction but can be made to occur by the addition or removal of energy to a system at equilibrium. For a process to be spontaneous, the delta S of the universe must be positive.

Third law:the entropy of a perfect crystaline substance is zero at absoulte zero. As tempertature increases,molecular motion increases,causing an increase in the number of possible arrangements of the molecules and in the number of accessible energy states,among which the system's energy aren be dispersed. ex: a solid cryslaline is melted ( increased temp in order to melt) it changes states and goes to a liquid ( increase temp) goes to gas. As it goes from solid to gaseous state the arragement change and more it as the ability to take up more space, this increase the entropy of the system.

1. Boltzmann distribution W=X^N W - the number of ways the molecules in a system can be arranged X - the number of cells the total volume of a system has been divided into N - the number of molecules in the system Ex. 4 cells and 3 molecules (does not gives 42, it gives 64) different ways the molecules can be arranged. Actually, since it is the number of cells raised to the power of the number of molecules, 4 cells and 3 molecules would be 4X4X4, for a total of 64 arrangements
 * Objective 3: Be able to predict the number of microstates using: **

2. Changes in volume W=X^N If there is an increase in the volume of the system then there is also an increase in the number of cells for the system and the number of arrangements for the molecules in the system. As well, if there is a reduction in the volume of the system there will be a reduction in the number of arrangements. Ex. 2 cells with 2 molecules gives 4 arrangements compared to 4 cells with 2 molecules gives 8 arrangements. Wouldnt with 4 cell and 2 molecules it be 4^2 for 16 arrangements.

3. Changes in number of molecules W=X^N If there is an increase in the number of molecules of the system then there is also an increase in the number of arrangements of the molecules within the system. As well, if there is a reduction in the number of molecules of the system there will be a reduction in the number of arrangements of the molecules within the system. Ex. 2 cells with 4 molecules gives 16 arrangements compared to 2 cells with 2 molecules gives 4 arrangements.

**Objective 4: Be able to predict the relative entropy of a molecule based on:** (explain how these characteristics can affect the relative entropy of a molecule, use examples). (Lets add some examples to each of them!!!)

1. Atomic number As molar mass increases in mono-atomic species (and thus atomic number goes up), so too does the stander entropy increase. For example, Chlorine has a higher entropy than Sodium. 2. Number of atoms When the phase and molar masses of two species are the same the entropy will be higher when molecular structure is more complex. For example O3 will have a higher entropy than F2.

3. Physical state : The physical state of a molecule determines its physical arrangement. ex. a liquid with have more entropy than a solid because of its ablilty to move. a solid will have the least amount of entropy due to its inabiltiy to move and a gas will have to greatest amount of entropy. 4. Number of electrons (ionic form) As the number of electrons goes up the entropy increases with it. (This is related to the atomic number because the electrons are determined from the atomic number and protons).

1. ∆H=∑〖n∆H_products-∑〖n∆H_reactants = enthalpy The standard enthalpy of reaction is the number of moles of each product multiplied by the enthalpy of that product minus the number of moles of each reactant multiplied by the enthalpy of that reactant.
 * Objective 5: Be able to use the thermodynamics formulas to determine changes in enthalpy, entropy, gibbs free energy and temperature: (What about if we add some example problems to this part? **

2. ∆S=∑〖n∆S_products-∑〖n∆S_reactants = entropy The change in entropy of a system is the difference between the entropy of the final state and the entropy of the initial state.

3. ∆G=∑〖n∆G_products-∑〖n∆G_reactants = the standard free energy of reaction (the free-energy change for a reaction when it occurs under the standard-state conditions-- that is, when reactants in their standard states are converted to products in their standard states.

4. ∆G=∆H-T∆S = gibbs free energy 5. Hess Law : as we know there is a change in enthalpy when reactants are converted to products. Hess's law tells us that this enthalpy change that occurs is the same whether the reaction takes place in one step or in a series of steps.

Practice Problem: Determine if the following reaction would happen spontaneously at room temperature. 2 SnO (s) + O2 (g) <-> 2 SnO2 (s) dH (KJ/mol) -280.71 / -577.63 dS (J/mol) 57.17 205.15 49.04 It would be spontaneous because dG is negative. -593.86(KJ/mol) = dH = 2(-577.63)-(-280.71*2) -.221 = dS = (1/1000) * 2(49.04)-(205.15+57.17*2) dG= - = -593.86 - (298*-.221)

Practice problem: Determine a temperatures range at which the following reaction would happen spontaneously. 2 SnO (s) + O2 (g) <-> 2 SnO2 (s) dH (KJ/mol) -280.71 / -577.63 dS (J/mol) 57.17 205.15 49.04 It would happen from 0-2687 K. 593.86 = -x (-.221) x = 2687

1. Changes in entropy with spontaneity of the reaction a spontaneous entropy reaction is a reaction in which there no intervention of continuity of outside help to keep the reaction going.
 * Objective 6: Be able to correlate the following concepts: (Delete after added: Provide formulas that show the connection!) **

2. Changes in entropy with changes in gibbs free energy Gibbs free energy can be use to determine the spontaneity or non spontaneity of any reaction or entropy change. this is made easy by the negative and positive sign in the formula( Gibbs formula). the is a relation between change in entropy and free energy, a negative value for free energy indicate the implication of spontaneous reaction

3. Changes in enthalpy with bond breakage/ bond formation Forming bonds = change in enthalpy is _exothermic reaction Breaking bonds = change in enthalpy is _ endothermic

4. Changes in enthalpy with changes in gibbs free energy enthalpy change is the same calculated the same way as change in entropy

5. Change in enthalpy with release or absorption of heat (internal energy) change in enthalpy with release of energy is exothermic and change in enthalpy with absorption of energy is endothermic.

When ∆H is negative, then ∆S is positive, and ∆G will be negative. When ∆H is positive, then ∆S is negative, and ∆G will be positive. When ∆H is negative, then ∆S is negative, and ∆G will be (negative when T∆S<∆H, and positive when T∆S>∆H) When ∆H is positive, then ∆S is positive, and ∆G will be (negative when T∆S>∆H, and positive when T∆S<∆H)
 * Objective 7: Be able to predict the sign of the change in enthalpy, entropy and gibbs free energy for a balanced chemical reaction. **

Practice Question. The freezing point of mercury is -39oC. Which of the following would be true for the freezing of mercury? (3 pts) a.dH is + and dS is – b.dH is - and dS is – c.dH is + and dS is + d.dH is - and dS is + e.Not enough information The answer to this problem is B. The answer is correct because the freezing of mercury is an exothermic process causing Delta H to be negative. Delta S is negative because it is going from a liquid to a solid. Practice question: A chemist working for a sporting good manufacturing company is assigned to design a cold pad and a heating pad to be incorporated in their new “xtreme sports” first aid kit. Using your knowledge on thermodynamics choose which of the following reactions would be the most appropriate for making a cold pack and which will be the most appropriate for making a heat pack. Give a brief explanation for your decision. (3 pts) a. Rx’n 1: Na2SO4 (s) + 2HNO3 (aq) -> H2SO4 (aq) + 2NaNO3 (s)

b. Rx’n 2: Na2O (S) + O2 (g) C (s) -> Na2CO3 (s) This reaction I would use to create the heat pack. It is an exothermic reaction that releases energy in the form of heat. When the closed system (Na2O) is exposed to the outside atmosphere (O2), the reaction will take place and provide heat.

c. Rx’n 3: CH3COOH (aq) -> CO2 (g) + CH4 (g) I would use this reaction to make the cold pack. Because the reaction results in a change from and aqueous solution to a gas the reaction is endothermic and therefore takes heat away from its surroundings and lowering their temperatures.