Chp3_dHstoich

Chp3_dHstoich - The Stoichiometry of Enthalpy Reactions...

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The Stoichiometry of Enthalpy Reactions Consider a generic reaction as follows: D C B A 4 3 2 1 + + where A, B, C, D are reactants and products. Further, let us assume that we have been given, or otherwise calculate: Hº = –253.7 kJ. The sign indicates that the reaction is exothermic. This value of the standard state reaction enthalpy is for the “reaction as written”. In other words we have the following equivalent stoichiometric identities: D mol kJ C mol kJ B mol kJ A mol kJ 4 7 . 253 3 7 . 253 2 7 . 253 1 7 . 253 - = - = - = - One might think of this exothermic reaction (energy released from the reaction system) as: kJ D C B A 7 . 253 4 3 2 1 + + + Note that the negative sign disappears as we put the energy released on the product side. The stoichiometric relationships above are no different from ones you have seen before, viz: C mol A mol B mol A mol 3 1 2 1 = etc. So, suppose we had been given, or worked out a reaction table and found, that 0.862 mol of B was the limiting reagent. What is the value of
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Chp3_dHstoich - The Stoichiometry of Enthalpy Reactions...

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