Unit 7: Thermochemistry

21. Which of the following processes is exothermic?

a) Evaporation of water
b) Photosynthesis
c) Combustion of methane
d) Sublimation of dry ice
Answer: c) Combustion of methane

22. What is the enthalpy change when 1 mole of a substance is formed from its elements in their standard states?

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

23. Which device is used to measure the heat of a chemical reaction?

a) Barometer
b) Calorimeter
c) Thermometer
d) Manometer
Answer: b) Calorimeter

24. What is the enthalpy change for a reaction when it is reversed?

a) The same as the forward reaction
b) Zero
c) Equal in magnitude but opposite in sign
d) Double the forward reaction
Answer: c) Equal in magnitude but opposite in sign

25. Which of the following is a state function?

a) Heat
b) Work
c) Enthalpy
d) Distance
Answer: c) Enthalpy

26. The specific heat capacity of a substance is defined as the amount of heat required to raise the temperature of:

a) 1 gram of the substance by 1°C
b) 1 mole of the substance by 1°C
c) 1 liter of the substance by 1°C
d) 1 kilogram of the substance by 1°C
Answer: a) 1 gram of the substance by 1°C

27. Which of the following represents the change in internal energy of a system?

a) ΔH
b) ΔS
c) ΔG
d) ΔU
Answer: d) ΔU

28. In an isolated system, what is the value of ΔU?

a) Positive
b) Negative
c) Zero
d) Infinite
Answer: c) Zero

29. What is the term for the heat content of a system at constant pressure?

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

30. When a gas expands and does work on its surroundings, the work done is considered:

a) Positive
b) Negative
c) Zero
d) Undefined
Answer: b) Negative