Chemical energy is released or absorbed from reactions in various forms. The mos

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:

rH= npfH(products) nrfH(reactants)

where n represents the stoichiometric coefficients.

Part A.Calculate the standard enthalpy change for the reaction

2A+B2C+2D

Use the following data:

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

Part B

For the reaction given in Part A, how much heat is absorbed when 3.10 mol of A reacts?

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

Explanation / Answer

Part A)

For the given reaction,

2A + B <==> 2C + 2D

standard enthalpy change,

dHo = dHo(products) - dHo(reactants)

taking values from the table,

dHo = (2 x 197 + 2 x -479) - (2 x -243 - 417)

        = 339 kJ/mol

Part B)

when 3.10 mol of A reacts

heat absorbed = 339 kJ/mol x 3.10 mol

                        = 1.05 x 10^3 kJ/mol

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