logging in or signing up Enthalpy and Entropy grazianir Download Post to : URL : Related Presentations : Let's Connect Share Add to Flag Embed Email Send to Blogs and Networks Add to Channel Copy embed code: Embed: Flash iPad Dynamic Copy Does not support media & animations Automatically changes to Flash or non-Flash embed WordPress Embed Customize Embed URL: Copy Thumbnail: Copy The presentation is successfully added In Your Favorites. Views: 2153 Category: Entertainment License: All Rights Reserved Like it (0) Dislike it (0) Added: January 07, 2010 This Presentation is Public Favorites: 0 Presentation Description No description available. Comments Posting comment... Premium member Presentation Transcript Enthalpy, Entropy and Spontaneity : Enthalpy, Entropy and Spontaneity Enthalpy (H) : Enthalpy (H) Amount of energy a sample contains at a certain pressure and temperature. (Heat Content) H H is sometimes used in place of q. Enthalpy Change (DH) : Enthalpy Change (DH) Enthalpy cannot be measured. Change in enthalpy is measured during a chemical reaction. H Heat of Reaction : Heat of Reaction Hrxn Heat released or absorbed per one mole of a reactant or product. Release of Heat - Exothermic rxn -H Absorption of Heat - Endothermic rxn +H Finding Hrxn : Finding Hrxn Hrxn = Hproducts – Hreactants Since H is not measured, calorimetry experiments are done. Example : Example 2 H2 + O2 2 H2O Hrxn = -5741.6 kJ Which contains more energy, the products or the reactants? Is this reaction exo- or endo- thermic? Another Notation : Another Notation Sometimes the enthalpy is indicated as part of the chemical equation. C + O2 CO2 -393.5 kJ Energy is a product (exo rxn) H is negative. N2 + O2 + 90 kJ NO Energy is a reactant (endo rxn) H is positive. Heat of Combustion : Heat of Combustion Amount of heat released in a combustion reaction. Combustion reactions can be recognized by the O2 reactant and the CO2 and H2O products. Hc is always negative. Entropy (S) : Entropy (S) The measure of disorder or randomness of a system. The more disorder there is the greater the entropy. In general changes tend to occur so the highest entropy is reached. Changes in Entropy : Changes in Entropy Spontaneity : Spontaneity Changes that happen on their own. Depends on enthalpy, entropy, and temperature. DG = DH – DST When DG is negative, a reaction will be spontaneous. Spontaneity : Spontaneity An exothermic reaction is more likely to be spontaneous than an endothermic one. A change that results in more entropy is more likely than one that results in less. Spontaneity : Spontaneity You do not have the permission to view this presentation. In order to view it, please contact the author of the presentation.