Lecture 5 1-16-08 Thermochemistry

Lecture 5 1-16-08 Thermochemistry - Enthalpy E is a state...

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Unformatted text preview: Enthalpy E is a state function doesnt depend on pathway Another state function Enthalpy, H H = E + (PV) Constant P, (PV) = P V H = E + P V = E w = q P (constant P) H = q P (constant P) H = nC P ( T) (general for a gas) Relationships of q, E, and H Depends on Pathway Constant T nC P T nC V T nC V T Constant V nC P T nC V T nC P T Constant P Enthalpy, H Internal Energy, E Heat, q Condition Thermochemistry Energy changes associated with chemical or nuclear reactions and phase changes Internal energy stored by chemical or nuclear bonds and/or intermolecular interactions in solids, liquids or gases Often reported under constant temperature conditions q , E and H are not zero for constant temperature very different than physical changes in gases. Exothermic process is any process that gives off heat transfers thermal energy from the system to the surroundings. Endothermic process is any process in which heat has to be supplied to the system from the surroundings. 2H 2 ( g ) + O 2 ( g ) 2H 2 O ( l ) + energy H 2 O ( g ) H 2 O ( l ) + energy energy + 2HgO ( s ) 2Hg ( l ) + O 2 ( g ) energy + H 2 O ( s ) H 2 O ( l ) Enthalpy (H) is used to quantify the heat flow into or out of a system in a process that occurs at constant pressure. H = H (products) H (reactants) H = heat given off or absorbed during a reaction at constant pressure H products < H reactants H < 0 H products > H reactants H > 0 6.3 Thermochemical Equations H 2 O ( s ) H 2 O ( l ) H = 6.01 kJ= 6....
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Lecture 5 1-16-08 Thermochemistry - Enthalpy E is a state...

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