Chemical energy is released or absorbed from reactions in various forms. The mos
ID: 939783 • Letter: C
Question
Chemical energy is released or absorbed from reactions in various forms. The most easily measurable form of energy comes in the form of heat, or enthalpy. The enthalpy of a reaction can be calculated from the heats of formation of the substances involved in the reaction:
Hrxn= npHf(products) nrHf(reactants)
where n represents the stoichiometric coefficients.
A). Calculate the standard enthalpy change for the reaction
2A+B2C+2D
Use the following data:
B).
For the reaction given in Part A, how much heat is absorbed when 2.60 mol of A reacts?
Substance Hf(kJ/mol) A -271 B -409 C 191 D -513
Explanation / Answer
A) Enthalpy of the reaction = Enthalpy of the products - Enthalpy of the reactants
=> 2 * (Enthalpy of C) + 2 * ( Enthalpy of D) - 2 * (Enthalpy of A) - Enthalpy of B
=> 2 * (191) + 2 * (-513) - 2 *(-271) -(-409)
=> 307 KJ/mol
B) Heat absorbed in the reaction
=> 2.60/2 * 307
=> 399.1 KJ
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