Energy changes in chemical and physical processes Knowledge-Based Download PDF

Questions

1. 1.

   Which statement best explains why chemical reactions typically involve substantially larger energy changes per mole than physical phase changes?

   • A) Physical changes always require a catalyst to overcome substantial activation energy barriers, whereas chemical reactions proceed spontaneously without any energy barrier.
   • B) Physical changes involve the complete rearrangement of valence electrons to create new atomic identities, whereas chemical reactions only alter the spatial distribution of intact molecules.
   • C) Chemical reactions create new energy through mass-energy conversion, whereas physical phase changes are strictly constrained by the conservation of thermal energy.
   • D) Chemical reactions involve breaking and forming strong intramolecular bonds, whereas physical phase changes primarily involve overcoming or establishing weaker intermolecular forces.
2. 2.

   During the vaporization of a pure liquid at its normal boiling point, how does the absorbed heat energy affect the kinetic and potential energies of the molecules?

   • A) The average kinetic energy remains constant while the potential energy of the molecules increases.
   • B) The average kinetic energy increases while the potential energy of the molecules remains constant.
   • C) Both the average kinetic energy and the potential energy of the molecules increase simultaneously.
   • D) The average kinetic energy increases while the potential energy of the molecules decreases.
3. 3.

   During a chemical reaction, bonds in the reactant molecules are broken and new bonds are formed in the product molecules. If the total energy absorbed to break the reactant bonds is less than the total energy released when forming the product bonds, which statement correctly describes the reaction?

   • A) The reaction is endothermic, and the products have a higher enthalpy than the reactants.
   • B) The reaction is exothermic, and the products have a lower enthalpy than the reactants.
   • C) The reaction is endothermic, and the products have a lower enthalpy than the reactants.
   • D) The reaction is exothermic, and the products have a higher enthalpy than the reactants.
4. 4.

   When a chemical reaction occurring in an aqueous solution causes the temperature of the surrounding solution to rise, how is the reaction classified, and what is the sign of its enthalpy change ($\Delta H$)?

   • A) It is endothermic, and $\Delta H > 0$.
   • B) It is endothermic, and $\Delta H < 0$.
   • C) It is exothermic, and $\Delta H < 0$.
   • D) It is exothermic, and $\Delta H > 0$.
5. 5.

   Which of the following processes is classified as endothermic because it absorbs thermal energy from the surroundings?

   • A) The sublimation of solid carbon dioxide
   • B) The condensation of water vapor
   • C) The combustion of propane gas
   • D) The crystallization of molten sodium chloride