Q: A 25.175 g pure silver coin (specific heat $$C = 0.235 \mathrm{J} \mathrm{g}^{-1} \mathrm{^{\circ}C}^{-1}) is $$heated from $$10.0^{\circ}C$ to 37.0$$^{\circ}$$C. $$How much heat is absorbed by the coin?

$$q = 25.175 \times 0.235 \times (37.0 - 10.0) = 278.1 \mathrm{J}$$

Q: Calculate the amount of heat required to raise the temperature of 105.39 g of water from $$15.4^{\circ}C$ to 45.8$$^{\circ}$$C. ($$Specific heat of water $$C = 4.184 \mathrm{J} \mathrm{g}^{-1} \mathrm{^{\circ}C}^{-1})$$

$$q = 105.39 \times 4.184 \times (45.8 - 15.4) = 13,370 \mathrm{J}$$

Q: A chemical reaction occurs at 298 K and results in a decrease of 2 moles of gas. What is the $$P-V$$ work done by the system? ($$R = 8.314 \mathrm{J} \mathrm{mol}^{-1} \mathrm{K}^{-1})$$

$$w = -2 \times 8.314 \times 298 = -4,950 \mathrm{J}$$

Q: In a bomb calorimeter, 1.00 g of sucrose ($$C_{12}H$$_{22}$$O_{11}) $$undergoes combustion, causing a temperature increase from $$24.922^{\circ}C$ to 28.331$$^{\circ}$$C. $$The heat capacity of the calorimeter is $$4.901 \mathrm{kJ}$$/^{\circ}$$C. $$What is the change in internal energy ($$\Delta U$) for the reaction?

$$\Delta U = -4.901 \times (28.331 - 24.922) = -16.71 \mathrm{kJ}$$

Q: Which of the following is the correct formula for calculating the standard enthalpy change of a reaction ($$\Delta H$$^{\circ}$$_{rxn}) $$using standard enthalpies of formation?

$$\Delta H$$^{\circ}$$_{rxn} = \sum \Delta H$$^{\circ}$$_f \text{(products)} - \sum \Delta H$$^{\circ}$$_f \text{(reactants)}$$

Question 1

Which of the following statements best describes the First Law of Thermodynamics?

Accepted Answer

Energy can neither be created nor destroyed; it can only be transferred from one object or system to another.

Question 2

A 25.175 g pure silver coin (specific heat $$C = 0.235 \mathrm{J} \mathrm{g}^{-1} \mathrm{^{\circ}C}^{-1}) is $$heated from $$10.0^{\circ}C$ to 37.0$$^{\circ}$$C. $$How much heat is absorbed by the coin?

Accepted Answer

$$q = 25.175 	imes 0.235 	imes (37.0 - 10.0) = 278.1 \mathrm{J}$$

Question 3

Which of the following is a correct expression for the change in internal energy ($$\Delta U) of a $$system?

Accepted Answer

$$\Delta U = q + w$$

Question 4

A reaction in a flask releases 890 J of heat to the surroundings and performs 450 J of work on the surroundings. What is $$\Delta U$$ for the system?

Accepted Answer

$$\Delta U = -890 - 450 = -1340 \mathrm{J}$$

Question 5

Which of the following best describes an exothermic reaction?

Accepted Answer

A reaction that releases heat to its surroundings; $$\Delta H \u003c 0.$$

Question 6

Calculate the amount of heat required to raise the temperature of 105.39 g of water from $$15.4^{\circ}C$ to 45.8$$^{\circ}$$C. ($$Specific heat of water $$C = 4.184 \mathrm{J} \mathrm{g}^{-1} \mathrm{^{\circ}C}^{-1})$$

Accepted Answer

$$q = 105.39 	imes 4.184 	imes (45.8 - 15.4) = 13,370 \mathrm{J}$$

Question 7

Which equation correctly represents the work done by a system during a volume change at constant pressure?

Accepted Answer

$$w = -P \Delta V$$

Question 8

A chemical reaction occurs at 298 K and results in a decrease of 2 moles of gas. What is the $$P-V$$ work done by the system? ($$R = 8.314 \mathrm{J} \mathrm{mol}^{-1} \mathrm{K}^{-1})$$

Accepted Answer

$$w = -2 	imes 8.314 	imes 298 = -4,950 \mathrm{J}$$

Question 9

Which of the following is true about state functions?

Accepted Answer

They are properties that depend only on the current state of the system, not on how it got there.

Question 10

In a bomb calorimeter, 1.00 g of sucrose ($$C_{12}H$$_{22}$$O_{11}) $$undergoes combustion, causing a temperature increase from $$24.922^{\circ}C$ to 28.331$$^{\circ}$$C. $$The heat capacity of the calorimeter is $$4.901 \mathrm{kJ}$$/^{\circ}$$C. $$What is the change in internal energy ($$\Delta U$) for the reaction?

Accepted Answer

$$\Delta U = -4.901 	imes (28.331 - 24.922) = -16.71 \mathrm{kJ}$$

Question 11

Which of the following correctly describes the relationship between enthalpy ($$H$$), internal energy ($$U$$), pressure ($$P$$), and volume ($$V$$)?

Accepted Answer

$$H = U + PV$$

Question 12

Given the reaction $$C_6H_{12}O_6$(s) \rightarrow 2 C_2H_5OH(l) + 2 CO_2$(g)$$, and the following standard enthalpies of formation: $$\Delta H_f$$^{\circ}$$(C_6H_{12}O_6$) = -1273.3 \mathrm{kJ/mol}$$, $$\Delta H_f$$^{\circ}$$(C_2H_5OH) = -277.6 \mathrm{kJ/mol}$$, $$\Delta H_f$$^{\circ}$$(CO_2$) = -393.5 \mathrm{kJ/mol}$$, calculate $$\Delta H$$^{\circ}$$ for the reaction.

Accepted Answer

$$\Delta H$$^{\circ}$$ = [2(-277.6) + 2(-393.5)] - [-1273.3] = -131.3 \mathrm{kJ}$$

Question 13

Which of the following is the correct formula for calculating the standard enthalpy change of a reaction ($$\Delta H$$^{\circ}$$_{rxn}) $$using standard enthalpies of formation?

Accepted Answer

$$\Delta H$$^{\circ}$$_{rxn} = \sum \Delta H$$^{\circ}$$_f 	ext{(products)} - \sum \Delta H$$^{\circ}$$_f 	ext{(reactants)}$$

Question 14

Which of the following statements about Hess's Law is correct?

Accepted Answer

The enthalpy change for a reaction is independent of the pathway taken, and is the sum of the enthalpy changes for each step.

Question 15

A 5.0 g cube of aluminum ($$C = 0.903 \mathrm{J} \mathrm{g}^{-1} \mathrm{^{\circ}C}^{-1}) at$$ $$45.8^{\circ}C$ is placed in 105.39$ g of water (C = 4.184$$ \mathrm{J} \mathrm{g}^{-1} \mathrm{^{\circ}C}^{-1}$$) at 15.4$$^{\circ}$$C. $$Assuming no heat loss, what is the final equilibrium temperature?

Accepted Answer

$$T_f = 16.98$$^{\circ}$$C$$

Question 16

Which of the following is NOT a unit of energy?

Accepted Answer

Mole (mol)

Question 17

Which of the following best describes the difference between heat and temperature?

Accepted Answer

Heat is the transfer of thermal energy due to a temperature difference, while temperature is a measure of the average kinetic energy of particles.

Question 18

Which of the following statements is true regarding the standard enthalpy of formation ($$\Delta H_f$$^{\circ}$$)?

Accepted Answer

It is the enthalpy change when 1 mole of a compound forms from its elements in their standard states.

Thermochemistry and Energy in Chemical Reactions (CHY 102)

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