Q: A 21.0 g rock rolls down a hill at a speed of 105.0 m/s. What is its kinetic energy?

$$E_k = \frac{1}{2} m v^2$ = \frac{1}{2} \times 0.021 \text{ kg} \times (105.0 \text{ m/s})^2$ = 115.8 \text{ J}$$

Q: A system absorbs 140 J of heat from the surroundings and does 85 J of work on the surroundings. What is the change in internal energy ($$\Delta E$$)?

$$\Delta E = q + w = 140 \text{ J} + (-85 \text{ J}) = 55 \text{ J}$$

Q: Which equation correctly relates heat, mass, specific heat, and temperature change?

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

Q: A fuel is burned in a cylinder equipped with a piston. The initial volume is 0.250 L, and the final volume is 0.980 L. If the piston expands against a constant pressure of 1.35 atm, how much work (in J) is done? ($$1 \text{ L-atm} = 101.3 \text{ J})$$

$$w = -P \Delta V = -1.35 \text{ atm} \times (0.980 - 0.250) \text{ L} = -0.9855 \text{ L-atm} \rightarrow -99.8 \text{ J}$$

Q: How much heat is released when 4.50 g of methane gas is burned in a constant-pressure system? ($$\Delta H = -890 \text{ kJ}$$ for $$1 \text{ mole CH}_4)$$

$$\text{Heat released} = 4.50 \text{ g} \times \frac{1 \text{ mole}}{16 \text{ g}} \times \frac{-890 \text{ kJ}}{1 \text{ mole}} = -250.31 \text{ kJ}$$

Question 1

A 21.0 g rock rolls down a hill at a speed of 105.0 m/s. What is its kinetic energy?

Accepted Answer

$$E_k = \frac{1}{2} m v^2$ = \frac{1}{2} 	imes 0.021 	ext{ kg} 	imes (105.0 	ext{ m/s})^2$ = 115.8 	ext{ J}$$

Question 2

Which of the following best describes an isolated system?

Accepted Answer

Neither energy nor matter can be exchanged with the surroundings.

Question 3

A system absorbs 140 J of heat from the surroundings and does 85 J of work on the surroundings. What is the change in internal energy ($$\Delta E$$)?

Accepted Answer

$$\Delta E = q + w = 140 	ext{ J} + (-85 	ext{ J}) = 55 	ext{ J}$$

Question 4

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

Accepted Answer

Enthalpy is a state function and depends only on the current state of the system.

Question 5

Which equation correctly relates heat, mass, specific heat, and temperature change?

Accepted Answer

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

Question 6

Which of the following is an example of an exothermic process?

Accepted Answer

Combustion of gasoline

Question 7

A fuel is burned in a cylinder equipped with a piston. The initial volume is 0.250 L, and the final volume is 0.980 L. If the piston expands against a constant pressure of 1.35 atm, how much work (in J) is done? ($$1 	ext{ L-atm} = 101.3 	ext{ J})$$

Accepted Answer

$$w = -P \Delta V = -1.35 	ext{ atm} 	imes (0.980 - 0.250) 	ext{ L} = -0.9855 	ext{ L-atm} ightarrow -99.8 	ext{ J}$$

Question 8

Which of the following is NOT a state function?

Accepted Answer

Work

Question 9

How much heat is released when 4.50 g of methane gas is burned in a constant-pressure system? ($$\Delta H = -890 	ext{ kJ}$$ for $$1 	ext{ mole CH}_4)$$

Accepted Answer

$$	ext{Heat released} = 4.50 	ext{ g} 	imes \frac{1 	ext{ mole}}{16 	ext{ g}} 	imes \frac{-890 	ext{ kJ}}{1 	ext{ mole}} = -250.31 	ext{ kJ}$$

Question 10

Which of the following statements about electrostatic potential energy ($$E_{el}) is $$correct?

Accepted Answer

$$E_{el} is $$positive for like charges and negative for opposite charges.

Question 11

Which system best represents an open system?

Accepted Answer

A beaker of water left uncovered on a table

Question 12

Which of the following is true about the enthalpy change ($$\Delta H) $$for a reaction?

Accepted Answer

$$\Delta H_{rxn} is $$equal in magnitude but opposite in sign for the reverse reaction.

Question 13

A system releases 672 kJ of heat to the surroundings and does 236 kJ of work on the surroundings. What is $$\Delta E$$?

Accepted Answer

$$\Delta E = q + w = -672 	ext{ kJ} + (-236 	ext{ kJ}) = -908 	ext{ kJ}$$

Question 14

Which of the following substances has the highest specific heat capacity at 298 K?

Accepted Answer

Water ($$H_2O)$$

Question 15

What is the specific heat capacity ($$C_s) of a $$metal if 25.0 g of it releases $$-669.4 J of $$heat and its temperature drops from $$100.0^\circC to$$ $$30.0^\circC$$?

Accepted Answer

$$C_s = \frac{q}{m 	imes \Delta T} = \frac{-669.4 	ext{ J}}{25.0 	ext{ g} 	imes (30.0 - 100.0)} = 0.383 	ext{ J/g} \cdot ^\circ	ext{C}$$

Question 16

Which of the following is a real-world example of potential energy being converted to kinetic energy?

Accepted Answer

A cyclist at the top of a hill starts riding down.

Question 17

Which process is endothermic?

Accepted Answer

Melting of ice

Question 18

What is the equation for pressure-volume work at constant pressure?

Accepted Answer

$$w = -P \Delta V$$

Question 19

Which property is extensive and depends on the amount of sample?

Accepted Answer

Enthalpy

Chapter 5: Thermochemistry – Energy, Enthalpy, and Calorimetry

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