Chemical Energy Part A Chemical energy is released or absorbed from reactions in

Question

Chemical Energy Part A 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 = np Hf (products) _ n, (reactants) where n represents the stoichiometric coefficients Calculate the standard enthalpy change for the reaction A+B2C+2D Use the following data: Substance (kJ/mol) 225 399 213 -499 Express your answer to three significant figures and include the appropriate units Hints .ae Units Submit My Answers Give Up

Explanation / Answer

The reaction is

2A + B ------------------> 2C + 2D

Given delta H f of A = -225

B = -399

C = +213

D = -499 all in kJ/mol

We know delta H 0rxn = sum of delta Hf of products - sum of delta H of reactants

= [2x(-499) +2(213)] - [ 2(-225) + (-399)]

= + 277 kJ

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