Q: A 2 kg block of aluminum ($$c = 900\ \mathrm{J/kg\cdot K}) is $$heated from $$20\ ^\circ \mathrm{C} to$$ $$50\ ^\circ \mathrm{C}. $$How much heat is required?

$$Q = 2 \times 900 \times (50-20) = 54,000\ \mathrm{J}$$

Q: A 0.5 kg sample of water at $$100\ ^\circ \mathrm{C} is $$converted to steam at $$100\ ^\circ \mathrm{C}. If $$the heat of vaporization of water is $$2.26 \times 10^6$\ \mathrm{J/kg}$$, how much heat is required?

$$Q = 0.5 \times 2.26 \times 10^6$ = 1.13 \times 10^6$\ \mathrm{J}$$

Question 1

Which of the following statements best describes the difference between heat and thermal energy?

Accepted Answer

Thermal energy is the energy of a system due to the motion of its atoms and molecules, while heat is energy transferred between a system and its environment because of a temperature difference.

Question 2

A rigid, sealed container of gas is used as a thermometer. If the pressure inside the container is measured to be zero at $$T_0 = -273$$\ ^\circ \mathrm{C}$$, what is the significance of this temperature?

Accepted Answer

It is absolute zero, the temperature at which all molecular motion ceases.

Question 3

Which equation correctly relates the Celsius and Kelvin temperature scales?

Accepted Answer

$$T_K = T_C + 273$$

Question 4

A 2 kg block of aluminum ($$c = 900\ \mathrm{J/kg\cdot K}) is $$heated from $$20\ ^\circ \mathrm{C} to$$ $$50\ ^\circ \mathrm{C}. $$How much heat is required?

Accepted Answer

$$Q = 2 	imes 900 	imes (50-20) = 54,000\ \mathrm{J}$$

Question 5

Which of the following best explains why ice floats on water?

Accepted Answer

Water expands upon freezing because of its polar molecular structure, making ice less dense than liquid water.

Question 6

A copper rod of length $$L is $$heated so its temperature increases by $$\Delta T. If $$the coefficient of linear expansion is $$\alpha$$, what is the change in length $$\Delta L$$?

Accepted Answer

$$\Delta L = \alpha L \Delta T$$

Question 7

During a phase change from solid to liquid, what happens to the temperature of the substance as heat is added?

Accepted Answer

The temperature remains constant until the phase change is complete.

Question 8

Which of the following equations describes the heat required to melt $$m$$ kilograms of ice at $$0\ ^\circ \mathrm{C}$$? ($$L_f is $$the heat of fusion for ice.)

Accepted Answer

$$Q = m L_f$$

Question 9

A 0.5 kg sample of water at $$100\ ^\circ \mathrm{C} is $$converted to steam at $$100\ ^\circ \mathrm{C}. If $$the heat of vaporization of water is $$2.26 	imes 10^6$\ \mathrm{J/kg}$$, how much heat is required?

Accepted Answer

$$Q = 0.5 	imes 2.26 	imes 10^6$ = 1.13 	imes 10^6$\ \mathrm{J}$$

Question 10

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

Accepted Answer

The change in internal energy of a system is equal to the heat added to the system plus the work done on the system: $$\Delta E_{int} = Q + W$$

Question 11

A 0.2 kg piece of copper ($$c = 385\ \mathrm{J/kg\cdot K}) at$$ $$150\ ^\circ \mathrm{C} is $$dropped into 0.5 kg of water at $$20\ ^\circ \mathrm{C}. $$What is the final equilibrium temperature? (Assume no heat loss to the environment, $$c_{water} = 4190\ \mathrm{J/kg\cdot K})$$

Accepted Answer

About $$26\ ^\circ \mathrm{C}$$

Question 12

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

Accepted Answer

Compression

Question 13

The rate of heat transfer by conduction through a wall of area $$A$$, thickness $$L$$, and temperature difference $$\Delta T is $$given by:

Accepted Answer

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

Question 14

Which of the following statements about black-body radiation is correct?

Accepted Answer

A black body absorbs all incident radiation and emits the maximum possible radiation at a given temperature.

Question 15

A phase diagram shows the phases of a substance as a function of:

Accepted Answer

Pressure and temperature

Question 16

Which of the following best explains why sweating cools the human body?

Accepted Answer

Evaporation of sweat removes thermal energy from the skin.

Question 17

A metal rod is heated at one end. Which mechanism is primarily responsible for the transfer of heat along the rod?

Accepted Answer

Conduction

Question 18

Which of the following is true about the direction of spontaneous heat transfer?

Accepted Answer

Heat always flows spontaneously from hot to cold.

Question 19

A 0.3 kg sample of ice at $$0\ ^\circ \mathrm{C} is $$placed in 0.5 kg of water at $$30\ ^\circ \mathrm{C}. $$How much heat is required to melt all the ice? ($$L_f = 3.33 	imes 10^5$\ \mathrm{J/kg})$$

Accepted Answer

$$Q = 0.3 	imes 3.33 	imes 10^5$ = 99,900\ \mathrm{J}$$

Heat and the First Law of Thermodynamics: Study Notes

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