31. Which of the following reactions is likely to have a positive ΔH?

• A) Combustion of fuels
• B) Dissolution of ammonium nitrate in water
• C) Formation of water from hydrogen and oxygen
• D) Neutralization of an acid with a base
• Answer: B

32. When a system performs work on its surroundings, the internal energy of the system:

• A) Increases
• B) Decreases
• C) Remains constant
• D) Depends on the type of work done
• Answer: B

33. In an endothermic reaction, the heat is:

• A) Released
• B) Absorbed
• C) Unchanged
• D) Equal to the work done
• Answer: B

34. What does the term “enthalpy of formation” refer to?

• A) The heat change during a phase transition
• B) The heat change when one mole of a compound is formed from its elements in their standard states
• C) The total heat absorbed during a reaction
• D) The heat released when a compound decomposes
• Answer: B

35. The heat of reaction can be calculated using the enthalpies of formation of the reactants and products. This is based on:

• A) The First Law of Thermodynamics
• B) Hess’s Law
• C) The ideal gas law
• D) The law of conservation of mass
• Answer: B

36. The change in enthalpy for a reaction occurring at constant pressure is equal to:

• A) The heat added to the system
• B) The work done by the system
• C) The change in internal energy
• D) The heat removed from the system
• Answer: A

37. Which of the following can cause the internal energy of a system to change?

• A) Heat transfer
• B) Work done
• C) Chemical reactions
• D) All of the above
• Answer: D

38. Which of the following represents a state function?

• A) Work
• B) Heat
• C) Enthalpy
• D) All of the above
• Answer: C

39. The heat capacity at constant volume (C_V) is:

• A) The amount of heat required to raise the temperature of 1 mole of a substance at constant pressure
• B) The amount of heat required to raise the temperature of 1 mole of a substance at constant volume
• C) The amount of heat released during a phase change
• D) The heat required to change a substance from solid to liquid
• Answer: B

40. If a reaction has a negative ΔH and a positive ΔS, it is:

• A) Always spontaneous
• B) Always non-spontaneous
• C) Spontaneous at high temperatures
• D) Spontaneous at low temperatures
• Answer: C