Question 1

Which of the following best describes the difference between a coffee-cup calorimeter and a bomb calorimeter?

Accepted Answer

A coffee-cup calorimeter is used for measuring enthalpy changes at constant pressure, while a bomb calorimeter is used for measuring energy changes at constant volume.

Question 2

A gas expands from an initial volume of $$46\ \mathrm{L} to a $$final volume of $$64\ \mathrm{L}$$ against a constant external pressure of $$15\ \mathrm{atm}. $$Calculate the work done by the system. (Use $$w = -P\Delta V.)$$

Accepted Answer

$$w = -270\ \mathrm{L \cdot atm}$$

Question 3

Which of the following statements about enthalpy $$(\Delta H) is $$correct?

Accepted Answer

$$\Delta H is a $$state function and equals $$q at $$constant pressure.

Question 4

Given the reaction: $$\mathrm{CH_4$(g) + 2O_2(g) \rightarrow CO_2$(g) + 2H_2O(l)}$$ with $$\Delta H = -890\ \mathrm{kJ}$$, what does the negative sign of $$\Delta H$$ indicate?

Accepted Answer

The reaction is exothermic and releases heat to the surroundings.

Question 5

Calculate the enthalpy change when $$5.8\ \mathrm{g} of $$methane $$(\mathrm{CH_4$}) is $$burned at constant pressure, given $$\Delta H = -890\ \mathrm{kJ}$$ per mole of $$\mathrm{CH_4$}. ($$Molar mass of $$\mathrm{CH_4$} = 16.0\ \mathrm{g/mol})$$

Accepted Answer

$$-320\ \mathrm{kJ}$$

Question 6

Which of the following best describes a state function?

Accepted Answer

A property that depends only on the initial and final states, not on the process used.

Question 7

A student mixes $$100.0\ \mathrm{mL} of$$ $$1.0\ \mathrm{M}$$ NaOH with $$100.0\ \mathrm{mL} of$$ $$1.0\ \mathrm{M}$$ HCl in a coffee-cup calorimeter. The temperature rises from $$24.6^\circ\mathrm{C} to$$ $$31.3^\circ\mathrm{C}. $$Assuming the density is $$1.0\ \mathrm{g/mL}$$ and $$C_p = 4.184\ \mathrm{J/g^\circ C}$$, what is the heat evolved?

Accepted Answer

$$5.6\ \mathrm{kJ}$$

Question 8

Which of the following is true about the thermite reaction shown in the image (molten iron and sparks)?

Accepted Answer

It is an exothermic reaction that releases a large amount of energy.

Question 9

Using the table of standard enthalpies of formation, calculate $$\Delta H^\circ_{rxn}$$ for the reaction: $$2\mathrm{Al}(s) + \mathrm{Fe_2O_3}(s) \rightarrow \mathrm{Al_2O_3}(s) + 2\mathrm{Fe}(s).$$

Accepted Answer

$$-850\ \mathrm{kJ}$$

Question 10

Which equation correctly relates the change in internal energy $$(\Delta E) to $$heat $$(q)$$ and work $$(w)$$?

Accepted Answer

$$\Delta E = q + w$$

Question 11

Which of the following best describes the sign conventions for heat $$(q)$$ and work $$(w) in $$thermochemistry?

Accepted Answer

$$q is $$positive when heat is absorbed by the system; $$w is $$positive when work is done on the system.

Question 12

Which of the following is the correct formula for calculating the quantity of heat absorbed or released by a substance?

Accepted Answer

$$q = m \cdot C_p \cdot \Delta T$$

Question 13

Which of the following statements about bond energies is correct?

Accepted Answer

Energy must be absorbed to break bonds, and energy is released when bonds are formed.

Question 14

A reaction has $$\Delta H = +50\ \mathrm{kJ}. $$Which of the following is true?

Accepted Answer

The reaction is endothermic and absorbs heat.

Question 15

Which of the following is the correct expression for calculating the enthalpy change of a reaction using standard enthalpies of formation?

Accepted Answer

$$\Delta H_{rxn} = \sum \Delta H_f^\circ (	ext{products}) - \sum \Delta H_f^\circ (	ext{reactants})$$

Question 16

Which of the following best explains why water has a moderating effect on Earth's climate?

Accepted Answer

Water has a high specific heat capacity, so it absorbs and releases large amounts of heat with little temperature change.

Question 17

Which of the following is NOT a state function?

Accepted Answer

Work $$(w)$$

Question 18

Which of the following best describes the Law of Conservation of Energy?

Accepted Answer

Energy cannot be created or destroyed, only transformed from one form to another.

Thermochemistry: Energy, Enthalpy, and Calorimetry

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