8. Thermochemistry

Thermochemical Equations

Multiple Choice
Mothballs are composed primarily of the hydrocarbon naphthalene (C10H8). When 0.820 g of naphthalene burns in a bomb calorimeter, the temperature rises from 25.10 °C to 31.56 °C. If the heat capacity of the calorimeter is 5.11 kJ/°C, what is the change in internal energy (ΔErxn) for the combustion of naphthalene?
Multiple Choice
Using the given reactions, what is the enthalpy change (ΔH°) for the reaction: 2 CO(g) + 2 H2(g) → CO2(g) + H2O(g)?
Multiple Choice
Nitromethane (CH₃NO₂), sometimes used as a fuel for drag racing, burns according to the following reaction:

4 CH₃NO₂ (l) + 7 O₂ (g) → 4 CO₂ (g) + 6 H₂O (g) + 4 NO₂ (g) ∆Hº = – 2441.6 kJ

How much heat is released by burning 125.0 g of nitromethane (MW:61.044 g/mol)?
Multiple Choice
Consider the following reaction:
2 C₆H₆ (l) + 15 O₂ (g) → 12 CO₂ (g) + 6 H₂O (g) ∆Hº = – 6278 kJ
What volume of benzene (C₆H₆, d = 0.880 g/mL, molar mass = 78.11 g/mol) is necessary to evolve 5.19 x 10⁹ kJ of heat?
Multiple Choice
The creation of liquid methanol is accomplished by the hydrogenation of carbon monoxide:
CO (g) + 2 H₂ (g) → CH₃OH (l) ∆Hº = – 128.1 kJ
How much heat (in kJ) is released when 125.0 g CO reacts with 2.32 x 10² g H₂?
Multiple Choice
Consider two identical iron nails: One nail is heated to 95℃, the other is cooled to 15℃. The two nails are placed in a coffee cup calorimeter and the system is allowed to come to thermal equilibrium. What is the final temperature of the two nails?
Open Question
Which answer best describes the transfer of heat that occurs when 1.50 mol of H₂ reacts?
Multiple Choice
Calculate the standard enthalpy change (ΔH°_rxn) for the reaction: 2 Br₂(l) + C₂H₂(g) → C₂H₂Br₄(l) using the given bond energies.
Multiple Choice
Given the thermochemical equation 3 C(s) + 4 H₂(g) → C₃H₈(g), what is the standard enthalpy change of formation (ΔHf°) for propane, C₃H₈(g)?
Multiple Choice
A 100.0 mL sample of 0.300 M NaOH is mixed with a 100.0 mL sample of 0.300 M HCl in a coffee cup calorimeter. If both solutions were initially at 35.00°C and the temperature of the resulting solution was recorded as 37.00°C, determine the ΔH°rxn (in kJ/mol) for the neutralization reaction.
Multiple Choice
A 100 mL sample of 0.3 M NaOH is mixed with a 100 mL sample of 0.3 M HCl in a coffee cup calorimeter. If both solutions were initially at 35°C and the temperature of the resulting solution was recorded as 37°C, determine ΔH_rxn (in units of kJ/mol NaOH) for the reaction.
Multiple Choice
A 6.61 g sample of an unknown salt (MM = 116.82 g/mol) is dissolved in 150.00 g of water in a coffee cup calorimeter. Before placing the sample in the water, the temperature of the salt and water is 23.72 °C. After the salt has completely dissolved, the temperature of the solution is measured to be 20.15 °C. What is the enthalpy change (ΔH) for the dissolution of the salt in kJ/mol?
Multiple Choice
What is the enthalpy change (ΔH) for the dissolution of 2.50 g of substance X in water, given that the temperature of the solution increases from 12.0 °C to 27.0 °C?
Multiple Choice
A sample of steam with a mass of 0.521 g at a temperature of 100 °C condenses into an insulated container holding 4.45 g of water at 2.0 °C. For water, ΔHvap = 40.7 kJ/mol and Cwater = 4.18 J/(g·°C). Assuming that no heat is lost, what is the final temperature of the water in the container?
Multiple Choice
An 8.5 g ice cube is placed into 255 g of water. Calculate the temperature change in the water upon the complete melting of the ice. Assume that all of the energy required to melt the ice comes from the water. The enthalpy of fusion (ΔH_fusion) is 6.02 kJ/mol. What is the temperature change in the water?