CART Thermochemistry and Energy 2 — Questions and Answers
Question 1: Which calorimetry equation relates heat, mass, specific heat, and temperature change?
- q = mΔH
- q = mcΔT (Correct answer)
- q = nRT
- q = PΔV
Correct answer: q = mcΔT
The equation q = mcΔT calculates heat by multiplying mass, specific heat capacity, and change in temperature.
Question 2: In a coffee-cup calorimeter experiment, the temperature of the solution rises after mixing two reactants. The reaction is:
- Endothermic
- Exothermic (Correct answer)
- Neutral
- Reversible only
Correct answer: Exothermic
A temperature rise in the calorimeter means the reaction released heat to the solution, indicating an exothermic reaction.
Question 3: The heat of combustion of propane (C₃H₈) is –2220 kJ/mol. How much heat is released by burning 0.5 mol of propane?
- –4440 kJ
- –1110 kJ (Correct answer)
- +1110 kJ
- +2220 kJ
Correct answer: –1110 kJ
Multiplying 0.5 mol × (–2220 kJ/mol) = –1110 kJ, meaning 1110 kJ of heat is released.
Question 4: Which symbol represents the heat of a reaction measured at constant volume?
- ΔH
- ΔU (or ΔE) (Correct answer)
- ΔS
- ΔG
Correct answer: ΔU (or ΔE)
Internal energy change (ΔU or ΔE) represents heat flow at constant volume, as measured in a bomb calorimeter.
Question 5: Bond breaking in a chemical reaction requires ________ energy, while bond forming ________ energy.
- releases; absorbs
- absorbs; releases (Correct answer)
- absorbs; absorbs
- releases; releases
Correct answer: absorbs; releases
Energy must be absorbed (input) to break bonds, and energy is released (output) when new bonds form.
Question 6: If the products of a reaction have higher enthalpy than the reactants, the ΔH for the reaction is:
- Negative
- Zero
- Positive (Correct answer)
- Cannot be determined
Correct answer: Positive
ΔH = H(products) – H(reactants); if products have higher enthalpy, ΔH is positive, indicating an endothermic reaction.
CART Thermochemistry and Energy 2
Which calorimetry equation relates heat, mass, specific heat, and temperature change?