The chemical reaction for the burning of hydrogen is 2H 2 O ? 2H 2 + O 2 . The m

Question

The chemical reaction for the burning of hydrogen is 2H2O ? 2H2 + O2. The molecular structures are schematically represented by the figure below.

The bond energies for a single molecule are as follow:

- O-H bond: 4.52 eV

- O-O (double) bond: 5.17 eV

- H-H bond: 4.77 eV.

A. In which direction does the reaction require an energy input?

a. 2H2O ? 2H2 + O2

b. 2H2O ? 2H2 + O2    

c. 2H2O ? 2H2 + O2 (both directions)

d. Neither

B. How much energy input is required? ____eV

C. Given that we choose separated atoms at rest as our zero of potential energy, which of the following bar charts gives a reasonable representation of how energy is balanced in the reaction? If none work, choose N.

D. Briefly explain the reasoning behind your choice of chart.

Explanation / Answer

Solution :-

Lets calculate the energy change of the reaction

Delta H rxn = sum of bond energy of reactant – sum of bond energy of products

                    = [(4*O-H)] –[(1*O=O)+(2-H-H)]

                   = [4*4.52] –[(1*5.17)+(2*4.77)]

                    = 3.37 eV

So the enthalpy change of the reaction is positive means reaction is endothermic

So the energy input needed in forward direction

So answer is option A = 2H2O ------ > 2H2 + O2

b) energy input needed is 3.37 eV

c) reaction is endothermic so the energy of the reactant is less than energy of the products

so the bar chart C is correct

d) bar chart C is correct because energy is added to the reactant side to produce the products.

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