Chapter 1. Discussion Questions

1.1 Discussion Questions

1. Chemical reactions and the potential and kinetic energy of a system: Atoms and molecules in a system transfer energy to or from the surroundings depending on changes in kinetic energy (energy of motion) and potential energy (energy associated with interatomic or intermolecular attractions).

• Explain why the rearrangements of atoms in an exothermic chemical reaction transfers heat to the surroundings.

1.2 Discussion Questions

2. Average bond enthalpies: The energies required to break a bond between any two atoms have been tabulated. Examine the bond energies in the table on Slide X. [should probably be a link]

• How does the bond order affect the average bond enthalpy? Give examples as evidence to support your answer.
• How does bond polarity affect the average bond enthalpy? Give examples as evidence to support your answer.
• How can you explain the trend in the average bond enthalpies of H-H, H-C, H-O, and H-F?
• How much energy is required to break all the bonds in CH₄?
• Use the average bond enthalpies to determine the energy released when water forms from atoms.

2H(g) + O(g) → H₂(g)

1.3 Discussion Questions

3. Calculations of reaction enthalpies using average bond energies: The heat associated with a chemical change can be estimated from the energy required to break all the bonds in the reactant molecules and the energy released when the bonds in the product molecules form.

• A combustion reaction is a reaction between a substance and oxygen, O₂ (g), to produce carbon dioxide, CO₂ (g), and water, H₂O (g). Write the balanced chemical equation for the combustion of methane, CH₄, methanol, CH₃OH, and formic acid, HCOOH. Estimate the heat of these three reactions using bond enthalpies. What pattern do you notice in the magnitude of the heats of these three reactions?
• Does it matter if the water produced in a combustion reaction is gaseous or liquid? Explain your thinking.

2H(g) + O(g) → H₂(g)