Energy changes in chemical and physical processes Knowledge-Based Practice

Questions

1. 1.

   During the boiling of a pure liquid at constant pressure, heat is continuously added to the system, yet its temperature remains constant. Which of the following best explains this observation in terms of particulate energy changes?

   • A) The absorbed thermal energy increases the average kinetic energy of the particles while their potential energy remains unchanged.
   • B) The absorbed thermal energy is used to break intramolecular covalent bonds, converting the molecules into separate atoms.
   • C) The absorbed thermal energy is transferred entirely to the surroundings as heat, preventing any net gain in internal energy.
   • D) The absorbed thermal energy increases the potential energy of the system by overcoming intermolecular attractions rather than increasing the average kinetic energy of the particles.
2. 2.

   Which of the following statements correctly compares the typical magnitude of energy changes accompanying physical processes with those accompanying chemical processes?

   • A) Physical processes require substantially larger energy changes because strong intramolecular covalent bonds must be broken.
   • B) Chemical processes exhibit much smaller enthalpy changes because they only involve disrupting weak dispersion forces.
   • C) Physical processes generally involve much smaller enthalpy changes per mole because they only disrupt relatively weak intermolecular attractions rather than chemical bonds.
   • D) Physical and chemical processes operate on identical energy scales because both require identical amounts of energy to overcome electrostatic forces.
3. 3.

   In an exothermic chemical reaction occurring at constant pressure, which statement correctly describes the change in enthalpy ($\Delta H$) of the system and the resulting thermal interaction with the surroundings?

   • A) $\Delta H < 0$, because the products have lower enthalpy than the reactants, causing heat to be released to the surroundings.
   • B) $\Delta H > 0$, because the products have higher enthalpy than the reactants, causing heat to be absorbed from the surroundings.
   • C) $\Delta H < 0$, because the system absorbs thermal energy from the surroundings to lower the enthalpy of the products.
   • D) $\Delta H > 0$, because the release of thermal energy increases the total internal energy stored in the products.
4. 4.

   Which statement correctly describes the fundamental energy changes associated with the breaking and forming of chemical bonds during a reaction?

   • A) Both breaking bonds and forming bonds release energy to the surroundings.
   • B) Breaking bonds requires an absorption of energy, whereas forming bonds releases energy.
   • C) Breaking bonds releases energy to the surroundings, whereas forming bonds requires an absorption of energy.
   • D) Both breaking bonds and forming bonds require a net absorption of energy from the surroundings.
5. 5.

   Which of the following processes occurs with the net absorption of heat from the surroundings, classifying it as endothermic?

   • A) Condensation of water vapor
   • B) Combustion of natural gas
   • C) Sublimation of solid iodine
   • D) Neutralization of hydrochloric acid with sodium hydroxide

Answers and step-by-step solutions appear after you finish the test.