<p> REACTION DYNAMICS </p><p>All chemical reactions proceed toward :</p><p>A. Maximum Disorder ( S ) ( + S is favorable )</p><p>Entropy – measure of the disorder of a system ( S )  All systems strive toward increased entropy à prefer greater disorder  Nature favors high randomness over order: 1. conversion of solid to liquid or liquid to gas - gases are more disordered than liquids - liquids are more disordered than solids 2. conversion of complex molecules into more simple ones - more smaller molecules/particles from fewer larger ones 3. weakening of ionic forces - breaking of ionic bonds in very structured crystal structures 4. dissolving substances - dissolved substances are more disordered than solids 5. reactions with more moles of product gases than reactant gases - the greater the number of gas molecules the more disorder</p><p>B. Minimum Energy ( H ) (- H is favorable)</p><p>Enthalpy – heat content of a system ( H )  All systems strive to release energy à prefer to be exothermic - stronger bonds are made than are broken (forming bonds releases energy) - the product will always contain the most powerful interactions</p><p> thermochemical equation – chemical equation that includes the amount of energy required or released</p><p> heat of reaction- the heat that is released or absorbed during a chemical reaction </p><p>If the change in enthalpy is decreasing (giving off heat), the reaction is EXO In exothermic reactions the heat appears on the products side of the equation.</p><p>- H = EXO [ H is negative if the reaction is exothermic ]</p><p>If the change in enthalpy is increasing (taking in heat), the reaction is ENDO In endothermic reactions the heat appears on the reactants side of the eq.</p><p>+ H = ENDO [ H is positive if the reaction is endothermic ] C. Spontaneity – the likelihood of a reaction to proceed without outside intervention -- spontaneous reactions happen by themselves; they can be fast or slow (Not all reactions are spontaneous.) </p><p>A reaction will occur spontaneously only if:</p><p>1. both enthalpy and entropy are favorable - energy is released (exo) and disorder increases</p><p>2. favorable enthalpy overcomes unfavorable entropy - the release of heat overcomes decreased disorder</p><p>3. favorable entropy overcomes unfavorable enthalpy - increased disorder overcomes absorption of heat</p><p>Example A: Na2CO3 (s)  Na2O (s) + CO2 (g) + 1131.1 kJ</p><p>This reaction will occur spontaneously because:</p><p> enthalpy is favorable – reaction is exothermic ( H = -1131.1 kJ)  entropy is favorable – products formed are more disordered than reactants (more simpler molecules formed & more product gases)</p><p>Example B: 2 O2 (g) + N2 (g) + 67.7 kJ  2 NO2 (g) </p><p>This reaction will not occur spontaneously because:</p><p> enthalpy is unfavorable – reaction is endothermic ( H = + 67.7kJ)  entropy is unfavorable – products formed are less disordered than reactants (fewer complex molecules formed & more reactant gases)</p><p>Example C: 3 H2 (g) + N2 (g)  2 NH3 (g) + 46.19 kJ</p><p> Shows favorable enthalpy (reaction is exothermic)  Shows unfavorable entropy (reactants are more disordered than products)</p><p>This reaction will occur spontaneously only if favorable enthalpy overcomes unfavorable entropy.</p><p>This reaction will not occur spontaneously if unfavorable entropy overcomes favorable enthalpy.</p>