Q: A 70 kg person’s body temperature increases from 37°C to 39°C. If the specific heat of the body is $$3400\ \mathrm{J/kg\ K}$$, how much energy is required?

$$4.8 \times 10^5$\ \mathrm{J}$$

Q: A 1 kg block of ice at 0°C is melted completely. If the heat of fusion for water is $$3.33 \times 10^5$\ \mathrm{J/kg}$$, how much heat is required?

$$3.33 \times 10^5$\ \mathrm{J}$$

Question 1

Which of the following best describes the first law of thermodynamics?

Accepted Answer

The change in a system’s thermal energy is equal to the sum of the work done on the system and the heat added to the system: $$\Delta E_{th} = W + Q.$$

Question 2

A gas in a piston is compressed at constant pressure. Which equation gives the work done on the gas?

Accepted Answer

$$W = -p \Delta V$$

Question 3

During an isothermal expansion of an ideal gas, which of the following is true?

Accepted Answer

The change in thermal energy $$\Delta E_{th} is $$zero.

Question 4

A 70 kg person’s body temperature increases from 37°C to 39°C. If the specific heat of the body is $$3400\ \mathrm{J/kg\ K}$$, how much energy is required?

Accepted Answer

$$4.8 	imes 10^5$\ \mathrm{J}$$

Question 5

Which process is characterized by $$Q = 0$$ and $$pV^\gamma = 	ext{constant}$$ for an ideal gas?

Accepted Answer

Adiabatic

Question 6

A 200 g piece of iron at 120°C and a 150 g piece of copper at –50°C are placed in 300 g of ethyl alcohol at 20°C. If the specific heats are $$c_{Fe} = 449\ \mathrm{J/kg\ K}$$, $$c_{Cu} = 385\ \mathrm{J/kg\ K}$$, and $$c_{alcohol} = 2400\ \mathrm{J/kg\ K}$$, which equation would you use to find the final temperature $$T_f$$?

Accepted Answer

$$M_{Fe}c$$_{Fe}(T_f - 120) + $$M_{Cu}c$$_{Cu}(T_f + 50) + $$M_{alcohol}c$$_{alcohol}(T_f - 20) = 0$$

Question 7

Which of the following statements about heat and work is correct?

Accepted Answer

Heat is energy transferred due to a temperature difference, while work is energy transferred by a force causing displacement.

Question 8

A freezer is insulated with 5.0 cm thick Styrofoam ($$k = 0.035\ \mathrm{W/m\ K}) $$and has a total surface area of $$7.24\ \mathrm{m}^2. If $$the inside is at –20°C and the room is at 25°C, what is the rate of heat transfer into the freezer?

Accepted Answer

$$230\ \mathrm{W}$$

Question 9

Which equation gives the rate of heat transfer by conduction through a wall of area $$A$$, thickness $$L$$, and thermal conductivity $$k$$, with temperature difference $$\Delta T$$?

Accepted Answer

$$\frac{dQ}{dt} = \frac{kA\Delta T}{L}$$

Question 10

For an isothermal compression of an ideal gas, which formula gives the work done on the gas?

Accepted Answer

$$W = -nRT \ln \left( \frac{V_f}{V_i} \right)$$

Question 11

Which of the following is NOT a mechanism of heat transfer?

Accepted Answer

Compression

Question 12

A 1 kg block of ice at 0°C is melted completely. If the heat of fusion for water is $$3.33 	imes 10^5$\ \mathrm{J/kg}$$, how much heat is required?

Accepted Answer

$$3.33 	imes 10^5$\ \mathrm{J}$$

Question 13

Which of the following best describes the difference between specific heat $$c$$ and heat of transformation $$L$$?

Accepted Answer

$$c is $$the energy needed to change temperature, $$L is $$the energy needed for a phase change.

Question 14

In an adiabatic compression of air (diatomic gas, $$\gamma = 1.40$$), the volume decreases by a factor of 10. If the initial temperature is 30°C, what is the final temperature in kelvins?

Accepted Answer

$$761\ \mathrm{K}$$

Question 15

Which equation gives the rate of heat transfer by radiation from a surface of area $$A$$ and temperature $$T$$ with emissivity $$e$$?

Accepted Answer

$$\frac{dQ}{dt} = e\sigma AT^4$

Question 16

A system undergoes an isochoric process. Which of the following is true?

Accepted Answer

No work is done.

Question 17

For an ideal gas, the relationship between the molar specific heats at constant pressure and constant volume is:

Accepted Answer

$$C_P = C_V + R$$

Question 18

Which of the following statements about calorimetry is correct?

Accepted Answer

The net heat exchanged in an isolated system is zero: $$Q_1$$ + $$Q_2$$ + $$Q_3$$ + \ldots = 0$$.

Chapter 19: Work, Heat, and the First Law of Thermodynamics – Study Notes

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