Question 1

Which of the following best describes the difference between a state function and a path function in thermochemistry?

Accepted Answer

A state function depends only on the initial and final states of a system, not on the path taken.

Question 2

A gas expands from 10.0 L to 15.0 L against a constant external pressure of 2.0 atm. Calculate the work done by the gas. (Use $$w = -P\Delta V$$ and express your answer in L·atm.)

Accepted Answer

$$w = -5.0 L$$·atm

Question 3

Which of the following statements about exothermic and endothermic reactions is correct?

Accepted Answer

Exothermic reactions release heat, and the enthalpy change ($$\Delta H) is $$negative.

Question 4

A 50.0 g sample of metal at 100.0°C is placed in 100.0 g of water at 25.0°C. The final temperature of the system is 30.0°C. If the specific heat of water is $$4.18 J/g$$°C, what is the heat gained by the water?

Accepted Answer

$$q = 2090 J$$

Question 5

Which calorimeter setup is best suited for measuring the energy content of food, and why?

Accepted Answer

Bomb calorimeter, because it operates at constant volume and can contain explosive reactions.

Question 6

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

Accepted Answer

The reaction is exothermic and releases heat to the surroundings.

Question 7

Calculate the standard enthalpy change ($$\Delta H^\circ_{rxn}) $$for the reaction: $$2Al(s) + Fe_2O_3(s) \rightarrow Al_2O_3(s) + 2Fe(s)$$ using the following data: $$\Delta H^\circ_f [Al_2O_3(s)] = -1676 kJ/$$mol, $$\Delta H^\circ_f [Fe_2O_3(s)] = -826 kJ/$$mol, $$\Delta H^\circ_f [Al(s)] = 0$$, $$\Delta H^\circ_f [Fe(s)] = 0.$$

Accepted Answer

$$\Delta H^\circ_{rxn} = -850 kJ$$

Question 8

Which of the following best explains why water is effective at moderating Earth's temperature?

Accepted Answer

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

Question 9

A reaction has $$\Delta H = +120 kJ. $$Which of the following statements is true?

Accepted Answer

The reaction is endothermic and absorbs heat from the surroundings.

Question 10

Using bond energies, estimate the enthalpy change for the reaction: $$H_2(g$$) + $$F_2(g$$) \rightarrow 2HF(g)$$. Given: D(H-H) = 432$ kJ/mol, D(F-F) = 154$ kJ/mol, D(H-F) = 565$ kJ/mol.

Accepted Answer

$$\Delta H = -544 kJ$$

Question 11

Which of the following is true about the law of conservation of energy?

Accepted Answer

Energy can neither be created nor destroyed, only transformed from one form to another.

Question 12

A coffee-cup calorimeter contains 100.0 g of water at 25.0°C. If 5.00 g of NaOH is dissolved and the temperature rises to 32.0°C, what is the heat released? ($$C_p$$ for water = $$4.18 J/g$$°C)

Accepted Answer

$$q = 2930 J$$

Question 13

Which of the following best describes the process occurring in a bomb calorimeter?

Accepted Answer

A reaction occurs at constant volume, and the heat released is measured by the temperature change of the water.

Question 14

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

Accepted Answer

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

Question 15

If the enthalpy of formation ($$\Delta H_f^\circ) of$$ $$CO_2(g$$)$$ is -394$ kJ/mol and H_2O(l$$)$$ is -286$ kJ/mol, what is the enthalpy change for the combustion of one mole of CH_4$(g) to$$ $$CO_2(g$$)$$ and 2H_2O(l$$)$$, given $$\Delta H_f^\circ [$$CH_4(g$$)] = -75$$ kJ/mol?

Accepted Answer

$$\Delta H = -891 kJ$$

Question 16

Which of the following best describes the thermite reaction shown in the image?

Accepted Answer

It is a highly exothermic reaction used to produce molten iron.

Thermochemistry: Energy, Enthalpy, and Calorimetry

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