Endothermic and exothermic processes Knowledge-Based Practice

Questions

1. 1.

   In a balanced thermochemical equation, heat can be written directly on either side of the reaction arrow to denote energy transfer. Which of the following statements correctly pairs the placement of the heat term with the classification of the reaction and the sign of its enthalpy change ($\Delta H$)?

   • A) Heat written on the reactant side represents an exothermic reaction with $\Delta H > 0$.
   • B) Heat written on the product side represents an endothermic reaction with $\Delta H > 0$.
   • C) Heat written on the reactant side represents an endothermic reaction with $\Delta H < 0$.
   • D) Heat written on the product side represents an exothermic reaction with $\Delta H < 0$.
2. 2.

   When a sample of solid ammonium nitrate ($\text{NH}_4\text{NO}_3$) is dissolved in water inside an insulated container, the temperature of the resulting solution decreases significantly. Which of the following statements correctly classifies this dissolution process and identifies the direction of heat transfer?

   • A) The process is endothermic, and heat is transferred from the surrounding water to the dissolving solute.
   • B) The process is exothermic, and heat is transferred from the dissolving solute to the surrounding water.
   • C) The process is endothermic, and heat is released by the dissolving solute into the surrounding water.
   • D) The process is exothermic, and heat is absorbed by the dissolving solute from the surrounding water.
3. 3.

   Which of the following physical processes is exothermic?

   • A) Deposition of water vapor to form frost
   • B) Sublimation of solid carbon dioxide
   • C) Vaporization of liquid acetone
   • D) Melting of solid gallium
4. 4.

   Which of the following statements correctly explains why a chemical reaction is classified as exothermic in terms of bond breaking and bond formation?

   • A) Energy is released when reactant bonds break, whereas energy is absorbed when product bonds form.
   • B) The total energy absorbed to break bonds in the reactants is greater than the total energy released when bonds form in the products.
   • C) Stronger bonds are broken in the reactants than are formed in the products, leading to a net gain of thermal energy by the system.
   • D) The total energy released during the formation of bonds in the products is greater than the total energy absorbed to break bonds in the reactants.
5. 5.

   During a chemical reaction carried out at constant pressure, the total enthalpy of the products is greater than the total enthalpy of the reactants. Which of the following statements correctly describes this reaction and its thermal interaction with the surroundings?

   • A) It is an exothermic process with a negative $\Delta H$ that releases heat to the surroundings.
   • B) It is an exothermic process with a positive $\Delta H$ that absorbs heat from the surroundings.
   • C) It is an endothermic process with a positive $\Delta H$ that absorbs heat from the surroundings.
   • D) It is an endothermic process with a negative $\Delta H$ that releases heat to the surroundings.

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