Q: A 2.35 g snack chip is burned in a bomb calorimeter with a heat capacity of $$38.57\ \mathrm{kJ}\ ^\circ\mathrm{C}^{-1}. $$The temperature rises by $$2.70\ ^\circ\mathrm{C}. $$What is the energy released per gram of chip?

$$\frac{38.57 \times 2.70}{2.35} = 44.3\ \mathrm{kJ}\ \mathrm{g}^{-1}$$

Question 1

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

Accepted Answer

A state function depends only on the initial and final states of a system, while a path function depends on the specific process taken between those states.

Question 2

A chemical reaction occurs in a coffee-cup calorimeter. Which equation would you use to calculate the heat exchanged with the surroundings?

Accepted Answer

$$q = sm\Delta T$$

Question 3

Which of the following processes is exothermic?

Accepted Answer

Condensation of steam to liquid water

Question 4

A 2.35 g snack chip is burned in a bomb calorimeter with a heat capacity of $$38.57\ \mathrm{kJ}\ ^\circ\mathrm{C}^{-1}. $$The temperature rises by $$2.70\ ^\circ\mathrm{C}. $$What is the energy released per gram of chip?

Accepted Answer

$$\frac{38.57 	imes 2.70}{2.35} = 44.3\ \mathrm{kJ}\ \mathrm{g}^{-1}$$

Question 5

Which equation correctly expresses the First Law of Thermodynamics for a chemical system?

Accepted Answer

$$\Delta U = q + w$$

Question 6

If a reaction is carried out at constant volume in a bomb calorimeter, which equation gives the change in internal energy?

Accepted Answer

$$\Delta U = q_v$$

Question 7

Calculate the amount of energy required to heat $$95.0\ \mathrm{g} of $$water from $$22.5\ ^\circ\mathrm{C} to$$ $$95.5\ ^\circ\mathrm{C}$$, given the specific heat of water is $$4.184\ \mathrm{J}\ \mathrm{g}^{-1}\ ^\circ\mathrm{C}^{-1}.$$

Accepted Answer

$$q = (4.184)(95.0)(73.0) = 29,000\ \mathrm{J}$$

Question 8

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

Accepted Answer

Enthalpy is equal to the heat exchanged at constant pressure.

Question 9

Given the reaction $$\mathrm{CH}_4(g) + 2\ \mathrm{O}_2(g) \rightarrow \mathrm{CO}_2(g) + 2\ \mathrm{H}_2O(l)$$ with $$\Delta H = -890.4\ \mathrm{kJ}\ \mathrm{mol}^{-1}$$, how much energy is released when $$18.02\ \mathrm{g} of $$water is produced?

Accepted Answer

$$1781\ \mathrm{kJ}$$ released

Question 10

Which of the following is true about the sign conventions for heat ($$q) $$and work ($$w) in $$thermodynamics?

Accepted Answer

Heat absorbed by the system is positive ($$+q$$), work done by the system is negative ($$-w).$$

Question 11

Which of the following best describes an endothermic process?

Accepted Answer

A process in which heat is absorbed from the surroundings and the potential energy of the system increases.

Question 12

If the thermochemical equation $$\mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6(s) + 6\ \mathrm{O}_2(g) \rightarrow 6\ \mathrm{CO}_2(g) + 6\ \mathrm{H}_2O(l)$$ has $$\Delta H = -2803\ \mathrm{kJ}/\mathrm{mol}$$, what is $$\Delta H$$ for the reverse reaction?

Accepted Answer

$$+2803\ \mathrm{kJ}/\mathrm{mol}$$

Question 13

Which of the following is the correct formula for calculating the heat required to raise the temperature of an object using its heat capacity?

Accepted Answer

$$q = C \Delta T$$

Question 14

A metal pellet with a mass of $$85.00\ \mathrm{g} at$$ $$92.5\ ^\circ\mathrm{C} is $$dropped into $$150.00\ \mathrm{g} of $$water at $$23.1\ ^\circ\mathrm{C}. $$The final temperature is $$26.8\ ^\circ\mathrm{C}. If $$the specific heat of water is $$4.184\ \mathrm{J}\ \mathrm{g}^{-1}\ ^\circ\mathrm{C}^{-1}$$, what is the heat lost by the pellet?

Accepted Answer

$$q = (150.00)(4.184)(26.8 - 23.1) = 2,320\ \mathrm{J}$$

Question 15

Which of the following is NOT a correct guideline for manipulating thermochemical equations?

Accepted Answer

When reversing an equation, multiply $$\Delta H by$$ $$-1$$ and by the stoichiometric factor.

Question 16

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

Accepted Answer

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

Question 17

Which of the following statements about bond enthalpy is correct?

Accepted Answer

Breaking a chemical bond is an endothermic process, while forming a bond is exothermic.

Question 18

Which of the following best describes the energy changes when gasoline burns in an engine?

Accepted Answer

Potential chemical energy is converted to kinetic energy and heat.

Chapter 10: Thermodynamics – Energy Changes in Chemical Reactions

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