Chemical Energy H rxn= n p H f(products) n r H f(reactants) Part A 2A+B2C+2D Exp

Question

Chemical Energy

Hrxn= npHf(products) nrHf(reactants)

Part A

2A+B2C+2D

Express your answer to three significant figures and include the appropriate units.

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Chemical Energy

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.

Part A

Calculate the standard enthalpy change for the reaction

2A+B2C+2D

Use the following data: Substance Hf
(kJ/mol) A -253 B -395 C 213 D -517

Express your answer to three significant figures and include the appropriate units.

Hrxn =

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Explanation / Answer

Hrxn0= np Hf0 (products) nr Hfo (reactants)

n= stoichiometric coefficient

Hrxn0= standard enthalpy of the reaction

Hf0= formation standard enthalpy

2A+B2C+2D

Hrxn0= (2 x 213 kJ/mol + 2 x -517 kJ/mol) ( 2 x -253 kJ/mol + 1 x -395 kJ/mol)

Hrxn0= 293 kJ

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