Chem 1320 1st Edition Lecture 37Outline of Last Lecture I. Hess’s LawOutline of Current LectureI. How to ΔHII. Intermolecular ForcesCurrent Lecture I. How to ΔH=∑BE (reactants) - ∑BE (products) ∑ bonds broken - ∑ bonds formed 1. Break all of the bonds in the reactants and add the values up the same is done for the products and the product sum is subtracted from the reactant enthalpies. This difference is an estimate of a reaction enthalpy. 2. Break only the bonds that change in both the products and the reactant. Both methods require accurate Lewis structures to correctly identify the types and number of bonds broken. Bond enthalpies= chemical energyII. Intermolecular ForcesEvidence: the physical properties of matterPhase: a region of homogenous matter with well-defined boundariesMore Evidence: intermolecular forces distinct phases of matterInteractions between molecules. These interactions are fundamentally electrostatic Gases: average kinetic energy >> strength of intermolecular interactions. - Gases tend to expand and fill containersThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- Gases are compressible and the particles tend to freely move around one anotherLiquids: average kinetic energies = intermolecular interactions- Liquids still can assume the shape of a container - Particles can still move more around one another but liquids are less compressible and display different properties than gasesSolids: average kinetic energy << intermolecular interactions- Molecules are “locked” in position- Higher densities and are much less
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