Unit 7: Thermochemistry

31. Which of the following is a correct expression of the first law of thermodynamics?

a) ΔU = q + w
b) ΔU = q – w
c) ΔU = q × w
d) ΔU = q / w
Answer: a) ΔU = q + w

32. What is the enthalpy change associated with the complete combustion of 1 mole of a substance?

a) Heat of formation
b) Heat of reaction
c) Heat of fusion
d) Heat of combustion
Answer: d) Heat of combustion

33. In a constant volume calorimeter, which of the following is measured?

a) Enthalpy change
b) Internal energy change
c) Work done
d) Free energy change
Answer: b) Internal energy change

34. Which of the following processes involves a decrease in enthalpy?

a) Melting of ice
b) Evaporation of water
c) Condensation of steam
d) Sublimation of dry ice
Answer: c) Condensation of steam

35. The enthalpy change for a reaction depends on:

a) The initial and final states only
b) The path taken by the reaction
c) The rate of the reaction
d) The activation energy of the reaction
Answer: a) The initial and final states only

36. What is the heat change when 1 mole of a solid is converted to a liquid at its melting point?

a) Heat of combustion
b) Heat of formation
c) Heat of fusion
d) Heat of reaction
Answer: c) Heat of fusion

37. Which of the following factors can affect the enthalpy change of a reaction?

a) Temperature
b) Pressure
c) Concentration
d) All of the above
Answer: d) All of the above

38. The enthalpy change of a reaction can be calculated using which of the following equations?

a) Hess’s law
b) Boyle’s law
c) Charles’s law
d) Avogadro’s law
Answer: a) Hess’s law

39. What is the enthalpy change when 1 mole of a gas is dissolved in water?

a) Heat of reaction
b) Heat of solution
c) Heat of formation
d) Heat of combustion
Answer: b) Heat of solution

40. Which of the following is a measure of the disorder or randomness of a system?

a) Enthalpy
b) Entropy
c) Internal energy
d) Free energy
Answer: b) Entropy