Lecture 26 - Thermochemistry Enthalpy (H) is a...

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1 Enthalpy ( H ) is a thermodynamic quantity used to describe heat changes taking place at constant pressure. Endothermic process : heat has to be supplied to the system by the surroundings Exothermic process: heat is released to the surroundings from the system. The enthalpy change required to break a particular bond in one mole of gaseous molecules is the bond energy. Bond Energy is a measure of the stability of a molecule. Thermochemistry
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Bond Energies chemical reactions involve breaking bonds in reactant molecules and making new bonds to create the products the reaction ( HEAT ENERGY ) can be calculated by comparing the cost of breaking old bonds to the profit from making new bonds the amount of energy it takes to break one mole of a bond in a compound is called the bond energy in the gas state homolytically – each atom gets ½ bonding electrons
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Trends in Bond Energies the more electrons two atoms share, the stronger the covalent bond C≡C (837 kJ) > C=C (611 kJ) > C−C (347 kJ)
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This note was uploaded on 05/20/2008 for the course CHEM 115 taught by Professor Larkin during the Spring '08 term at Bloomsburg.

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Lecture 26 - Thermochemistry Enthalpy (H) is a...

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