A student investigates the combustion of gaseous methanol according to the balanced equation
2CH3OH(g)+3O2(g)⟶2CO2(g)+4H2O(g)
Selected average bond energies (in kJ mol−1) are provided in the table.
Bond
C–H
C–O
O–H
O=O
C=O (in CO2)
Energy
414
358
463
498
799
Assume that all C–O bonds in methanol are single bonds and that water is produced in the gaseous state.
Answer the following questions.
(1) Part 1: (a) Calculate the total energy required to break all bonds in the reactants for one mole of the balanced reaction as written.
(2) Part 2: (b) Calculate the total energy released upon forming all bonds in the products for the same extent of reaction.
(3) Part 3: (c) Determine the enthalpy change, ΔHrxn, in kJ mol−1 for the reaction as written and classify the reaction as endothermic or exothermic.
(4) Part 4: (d) On unlabeled axes with potential energy on the vertical axis and reaction progress on the horizontal axis, sketch a qualitative energy profile for the reaction. Clearly indicate the relative energy levels of reactants and products, label ΔHrxn, and show a plausible transition state.
(5) Part 5: (e) Identify which segment of your sketch corresponds predominantly to breaking the O=O bonds and justify your choice in terms of energy changes.