11 Entropy, S Entropy is a measure of the disorder or randomness of a system The greater the disorder the higher the entropy. Reaction of K with water

22 The entropy of liquid water is greater than the entropy of solid water (ice) at 0˚ C.

33 S (gases) > S (liquids) > S (solids) Entropy, S

44 Entropy of a substance increases with temperature. Molecular motions of heptane, C 7 H 16 Molecular motions of heptane at different temps. Entropy, S

55 If one compound breaks up into 2 – more disorder Ex: N2O4(g)→ 2NO2 (g) Entropy, S

66 Entropies of ionic solids depend on coulombic attractions. S o (J/Kmol) MgO26.9 NaF51.5 S o (J/Kmol) MgO26.9 NaF51.5 Entropy, S Mg 2+ & O 2- Na + & F -

77 Entropy and Temperature S increases slightly with T S increases a large amount with phase changes

88 End of class Reflection Table Define entropy in your own words, Table 2- list the variables or conditions that you must consider when comparing the entropy of two substances, or when trying to determine the relative change in entropy. Table 3 - If you have gas in a 1L vessel does it have more or less entropy as a gas in a 2L vessel? Table 4- What is the difference between entropy and enthalpy Table 5- Who is more disordered – NaCl(aq) or NaCl (s)?

99 Work on this part with your table, one of you first going over, explaining your answers to the other person Which member of the following pairs has the lesser predicted amount of entropy. CO2 (g) or CO2 (s) H2O (l) or H2O (s) Fe(s) at 25°C or Fe(s) at 100°C

1010 Energy Diagrams show how the species involved in a chemical reaction change their energy states Any line from the base (x-axis) to a point is the PE of that point

1111 Reaction Coordinate: describes how a chemical reaction proceeds. Reaction  activated complex  products Activated complex  this is a higher energy intermediate which the reactants transform into on their way to becoming products This is the highest energy point, found in between the reactants and products.

1212 Activation energy- the energy required to get to the activated complex  to start the reaction ∆H: the change in enthalpy. The difference in energy of the products and reactants. Because the energy is higher on the reactant side and lower on product side ∆H is negative Exothermic Activation Energy In the reverse Direction ??

energydiagram.htmhttp:// energydiagram.htm

1414 Equilibrium When both the forward and reverse reactions occur at the same rate. Can only occur in a closed system The quantities of reactants and products are not necessarily equal at equilibrium, its the rate at which the forward and reverse reaction run that are equal. Temperature effects equilibrium What would happen if a catalyst is added to a reaction at equilibrium?

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1616 Phase Equilibrium Exists between the solid and liquid phases of a substance. The rate of melting is the same as the rate of freezing (although not the same amount of ice/liquid will be present) The same is true for liquid-gas, the rate of evaporation is the same as condensation.

1717 Solution Equilibrium Solids in liquids exist in equilibrium in a saturated solution. When the rate of dissolving and recrystallizing are equal, equilibrium exists and the solution is saturated. C12H22O11(s)  C12H22O11(aq) Same is true for gas dissolved in liquid. In both cases, equilibrium is disturbed by a change in temp.

1818 Chemical Equilibrium When you first mix reactants no products are present. But as reaction proceeds you get product, this is the forward reaction As time goes on you will have more product than reactants, which will react to cause the reaction to move in the reverse direction. The slowing of the forward reaction and speeding up of the reverse continues until the rates of the forward and reverse are the same and now you have chemical equilibrium yay!!

1919 Important! If a system is not closed, equilibrium can not exist (nothing can leave the system) You can not have product until the reactants start making product (see graph)