Q: Calculate the amount of heat ($$q) $$required to raise the temperature of 50.0 g of water from 22.0 $$^\circC to 38.0$$ $$^\circC. $$The specific heat capacity of water is $$4.18\ \mathrm{J/g\cdot ^\circ C}.$$

$$q = 50.0\ \mathrm{g} \times 4.18\ \mathrm{J/g\cdot ^\circ C} \times (38.0 - 22.0)\ ^\circ\mathrm{C} = 3344\ \mathrm{J}$$

Q: Given the following standard enthalpies of formation: $$\Delta H_f^\circ(\mathrm{CO}_2(g)) = -393.5\ \mathrm{kJ/mol}$$, $$\Delta H_f^\circ(\mathrm{H}_2O(l)) = -285.8\ \mathrm{kJ/mol}$$, $$\Delta H_f^\circ(\mathrm{C}_6H_{12}O_6$(s)) = -1273\ \mathrm{kJ/mol}$$, calculate the standard enthalpy change for the combustion of glucose: $$\mathrm{C}_6H_{12}O_6$(s) + 6\mathrm{O}_2(g) \rightarrow 6\mathrm{CO}_2(g) + 6\mathrm{H}_2O(l).$$

$$\Delta H_{rxn}^\circ = [6 \times (-393.5) + 6 \times (-285.8)] - [-1273] = -2808\ \mathrm{kJ}$$

Q: A 100.0 g sample of iron at 100.0 $$^\circC is $$placed in 100.0 g of water at 20.0 $$^\circC. $$The final temperature is 24.0 $$^\circC. If $$the specific heat of iron is $$0.450\ \mathrm{J/g\cdot ^\circ C}$$ and water is $$4.18\ \mathrm{J/g\cdot ^\circ C}$$, what is the heat lost by the iron?

$$q = 100.0\ \mathrm{g} \times 0.450\ \mathrm{J/g\cdot ^\circ C} \times (24.0 - 100.0)\ ^\circ\mathrm{C} = -3420\ \mathrm{J}$$

Question 1

Which of the following best describes a state function, and which is NOT a state function?

Accepted Answer

Enthalpy ($$H) is a $$state function; work ($$w) is $$NOT a state function.

Question 2

A sample of gas absorbs 75 J of heat from the surroundings and does 107 J of work on the surroundings. What is the change in internal energy ($$\Delta E) of $$the system?

Accepted Answer

$$\Delta E = 75\ \mathrm{J} - 107\ \mathrm{J} = -32\ \mathrm{J}$$

Question 3

Which of the following statements about the First Law of Thermodynamics is correct?

Accepted Answer

Energy can be converted from one form to another, but cannot be created or destroyed.

Question 4

Which of the following equations correctly relates the change in internal energy ($$\Delta E$$), heat ($$q$$), and work ($$w$$)?

Accepted Answer

$$\Delta E = q + w$$

Question 5

A reaction occurs in a coffee-cup calorimeter at constant pressure. Which thermodynamic quantity does the heat measured correspond to?

Accepted Answer

Enthalpy change ($$\Delta H)$$

Question 6

Which of the following best describes an exothermic reaction?

Accepted Answer

A reaction that releases heat to the surroundings, resulting in $$q \u003c 0$$

Question 7

Calculate the amount of heat ($$q) $$required to raise the temperature of 50.0 g of water from 22.0 $$^\circC to 38.0$$ $$^\circC. $$The specific heat capacity of water is $$4.18\ \mathrm{J/g\cdot ^\circ C}.$$

Accepted Answer

$$q = 50.0\ \mathrm{g} 	imes 4.18\ \mathrm{J/g\cdot ^\circ C} 	imes (38.0 - 22.0)\ ^\circ\mathrm{C} = 3344\ \mathrm{J}$$

Question 8

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

Accepted Answer

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

Question 9

Which of the following reactions is a formation reaction for $$\Delta H_f^\circ$$?

Accepted Answer

$$\mathrm{C}(s) + \frac{1}{2}\mathrm{O}_2(g) \rightarrow \mathrm{CO}(g)$$

Question 10

Given the following standard enthalpies of formation: $$\Delta H_f^\circ(\mathrm{CO}_2(g)) = -393.5\ \mathrm{kJ/mol}$$, $$\Delta H_f^\circ(\mathrm{H}_2O(l)) = -285.8\ \mathrm{kJ/mol}$$, $$\Delta H_f^\circ(\mathrm{C}_6H_{12}O_6$(s)) = -1273\ \mathrm{kJ/mol}$$, calculate the standard enthalpy change for the combustion of glucose: $$\mathrm{C}_6H_{12}O_6$(s) + 6\mathrm{O}_2(g) \rightarrow 6\mathrm{CO}_2(g) + 6\mathrm{H}_2O(l).$$

Accepted Answer

$$\Delta H_{rxn}^\circ = [6 	imes (-393.5) + 6 	imes (-285.8)] - [-1273] = -2808\ \mathrm{kJ}$$

Question 11

Which of the following statements about calorimetry is correct?

Accepted Answer

A bomb calorimeter measures $$\Delta E at $$constant volume, while a coffee-cup calorimeter measures $$\Delta H at $$constant pressure.

Question 12

Which of the following is the correct expression for the heat required to raise the temperature of a substance?

Accepted Answer

$$q = m c \Delta T$$

Question 13

Which of the following is NOT a state function?

Accepted Answer

Work ($$w)$$

Question 14

A 100.0 g sample of iron at 100.0 $$^\circC is $$placed in 100.0 g of water at 20.0 $$^\circC. $$The final temperature is 24.0 $$^\circC. If $$the specific heat of iron is $$0.450\ \mathrm{J/g\cdot ^\circ C}$$ and water is $$4.18\ \mathrm{J/g\cdot ^\circ C}$$, what is the heat lost by the iron?

Accepted Answer

$$q = 100.0\ \mathrm{g} 	imes 0.450\ \mathrm{J/g\cdot ^\circ C} 	imes (24.0 - 100.0)\ ^\circ\mathrm{C} = -3420\ \mathrm{J}$$

Question 15

Which of the following is true regarding the standard enthalpy of formation ($$\Delta H_f^\circ) $$for an element in its most stable form?

Accepted Answer

$$\Delta H_f^\circ = 0$$

Question 16

Which of the following best describes Hess's Law?

Accepted Answer

The enthalpy change for a reaction is the same, regardless of the number of steps or pathway taken.

Question 17

Which of the following is the correct thermochemical equation for the standard enthalpy of formation of aluminum oxide ($$\mathrm{Al}_2\mathrm{O}_3(s)$$)?

Accepted Answer

$$2\mathrm{Al}(s) + \frac{3}{2}\mathrm{O}_2(g) \rightarrow \mathrm{Al}_2\mathrm{O}_3(s)$$

Question 18

A reaction is carried out in a bomb calorimeter. Which of the following is true?

Accepted Answer

The heat measured corresponds to $$\Delta E at $$constant volume.

Question 19

Which of the following best describes the difference between $$\Delta H$$ and $$q$$?

Accepted Answer

$$\Delta H is $$heat at constant pressure and is a state function; $$q is $$heat in general and is not a state function.

Chapter 9 Student Notes

Guida di studio - Domande di pratica

Study guide - Flashcard