Q: A system absorbs 22 J of heat and does 58 J of work. What is the change in internal energy ($$\Delta E$$)?

$$\Delta E = 22 \text{ J} + 58 \text{ J} = 80 \text{ J}$$

Q: Calculate the heat required to raise the temperature of 21.5 g of aluminum from 5.00 °C to 38.2 °C. ($$C_s = 0.897 \text{ J/g} \cdot ^\circ\text{C})$$

$$q = 21.5 \text{ g} \times 0.897 \text{ J/g} \cdot ^\circ\text{C} \times (38.2 - 5.00) = 641 \text{ J}$$

Q: What is the final temperature of 275 g of water at 21.5 °C after absorbing 15.8 kJ of heat? ($$C_s = 4.184 \text{ J/g} \cdot ^\circ\text{C})$$

$$T_f = \frac{15800}{275 \times 4.184} + 21.5 = 35.2^\circ\text{C}$$

Q: Which formula is used to calculate the heat absorbed by a solution in coffee-cup calorimetry?

$$q = m \times C_s \times \Delta T$$

Question 1

Which statement best describes the First Law of Thermodynamics?

Accepted Answer

The total energy of the universe is constant; energy can be transformed but not created or destroyed.

Question 2

Internal energy ($$E) is $$classified as a state function. What does this mean?

Accepted Answer

It depends only on the initial and final states, not the process.

Question 3

A system absorbs 22 J of heat and does 58 J of work. What is the change in internal energy ($$\Delta E$$)?

Accepted Answer

$$\Delta E = 22 	ext{ J} + 58 	ext{ J} = 80 	ext{ J}$$

Question 4

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

Accepted Answer

$$\Delta E = q + w$$

Question 5

If a chemical reaction in a beaker releases heat to the surroundings, how is the sign of $$q$$ and $$\Delta H$$ affected?

Accepted Answer

$$q is $$negative, $$\Delta H is $$negative

Question 6

Calculate the heat required to raise the temperature of 21.5 g of aluminum from 5.00 °C to 38.2 °C. ($$C_s = 0.897 	ext{ J/g} \cdot ^\circ	ext{C})$$

Accepted Answer

$$q = 21.5 	ext{ g} 	imes 0.897 	ext{ J/g} \cdot ^\circ	ext{C} 	imes (38.2 - 5.00) = 641 	ext{ J}$$

Question 7

What is the final temperature of 275 g of water at 21.5 °C after absorbing 15.8 kJ of heat? ($$C_s = 4.184 	ext{ J/g} \cdot ^\circ	ext{C})$$

Accepted Answer

$$T_f = \frac{15800}{275 	imes 4.184} + 21.5 = 35.2^\circ	ext{C}$$

Question 8

Which of the following best describes an exothermic reaction?

Accepted Answer

A reaction that releases heat to the surroundings and has a negative $$\Delta H.$$

Question 9

Which formula is used to calculate the heat absorbed by a solution in coffee-cup calorimetry?

Accepted Answer

$$q = m 	imes C_s 	imes \Delta T$$

Question 10

A 10.0 g piece of iron at 75.0 °C is placed in 125 g of water at 21.5 °C. If $$C_{s,H_2O} = 4.184 	ext{ J/g} \cdot ^\circ	ext{C}$$ and $$C_{p,Fe} = 25.15 	ext{ J/mol} \cdot ^\circ	ext{C}$$, what is the final equilibrium temperature?

Accepted Answer

$$T_f = 21.8^\circ	ext{C}$$

Question 11

Which of the following is true about heat capacity ($$C$$)?

Accepted Answer

It is an extensive property and depends on the amount of matter.

Question 12

In bomb calorimetry, which equation is used to determine the change in internal energy for a reaction?

Accepted Answer

$$\Delta E_{rxn} = -C_{cal} \Delta T$$

Question 13

Which statement correctly describes the difference between constant-volume and constant-pressure calorimetry?

Accepted Answer

Constant-volume calorimetry measures $$\Delta E$$, while constant-pressure calorimetry measures $$\Delta H.$$

Question 14

A reaction occurs in a coffee-cup calorimeter and causes the temperature of the solution to increase. What does this indicate about the reaction?

Accepted Answer

The reaction is exothermic.

Question 15

Which of the following equations is used to calculate pressure-volume work?

Accepted Answer

$$w = -P \Delta V$$

Question 16

If a system expands against a constant external pressure, what is the sign of the work ($$w) $$done by the system?

Accepted Answer

Negative, because the system loses energy to the surroundings.

Question 17

Which of the following is the correct unit for heat, work, and internal energy in thermochemistry?

Accepted Answer

Joules

Question 18

Which statement about enthalpy ($$H) is $$correct?

Accepted Answer

At constant pressure, the change in enthalpy ($$\Delta H) $$equals the heat exchanged ($$q_p).$$

Question 19

Which of the following reactions is exothermic?

Accepted Answer

Fe$$_2O$_3(s) + 3 CO(g$$) $$\rightarrow 2 Fe(s) + 3 CO$_2(g$$), $$\Delta H_{rxn} = -24.8 kJ$$

Thermochemistry: Internal Energy, Enthalpy, and Calorimetry

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