Q: A 2 kg block of ice at 0°C is melted completely to water at 0°C. If the latent heat of fusion for water is $$L_f = 3.33 \times 10^5$ \ \mathrm{J/kg}$$, how much heat is required for this process?

$$Q = 6.66 \times 10^5$ \ \mathrm{J}$$

Question 1

Which of the following best describes the concept of latent heat during a phase change?

Accepted Answer

Latent heat is the energy required to change the phase of 1 kg of a substance without changing its temperature.

Question 2

A 2 kg block of ice at 0°C is melted completely to water at 0°C. If the latent heat of fusion for water is $$L_f = 3.33 	imes 10^5$ \ \mathrm{J/kg}$$, how much heat is required for this process?

Accepted Answer

$$Q = 6.66 	imes 10^5$ \ \mathrm{J}$$

Question 3

Which statement about temperature and phase change is correct?

Accepted Answer

Temperature remains constant during a phase change even as heat is added.

Question 4

A freezer must remove heat from 1.5 kg of water at 20°C to make ice at -12°C. Which sequence of steps correctly describes the process?

Accepted Answer

Cool water to 0°C, freeze water at 0°C, cool ice to -12°C.

Question 5

According to the Zeroth Law of Thermodynamics, what happens when two objects reach the same temperature?

Accepted Answer

No heat flows between the objects; they are in thermal equilibrium.

Question 6

Which equation represents the First Law of Thermodynamics for a closed system?

Accepted Answer

$$\Delta U = Q - W$$

Question 7

During an isobaric process, which variable remains constant and what is the work done by the system?

Accepted Answer

Pressure remains constant; $$W = P \Delta V$$

Question 8

A gas undergoes an isothermal expansion. What is the change in internal energy ($$\Delta U) $$and the relationship between heat ($$Q) $$and work ($$W$$)?

Accepted Answer

$$\Delta U = 0$$; $$Q = W$$

Question 9

Which process involves no work done by the system and only heat transfer changes the internal energy?

Accepted Answer

Isovolumetric (isochoric) process

Question 10

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

Accepted Answer

No heat is exchanged with the surroundings ($$Q = 0)$$

Question 11

Which formula correctly describes the work done by a gas during a volume change at constant pressure?

Accepted Answer

$$W = P \Delta V$$

Question 12

A metal spoon is placed in a hot cup of coffee. Which heat transfer mechanism is primarily responsible for the spoon becoming hot?

Accepted Answer

Conduction

Question 13

Which equation describes the rate of heat flow by conduction through a material?

Accepted Answer

$$\frac{Q}{t} = kA \frac{T_h - T_c}{L}$$

Question 14

Which property makes a material a good thermal insulator?

Accepted Answer

Low thermal conductivity ($$k)$$

Question 15

Which process is responsible for heat transfer in fluids due to bulk movement of molecules?

Accepted Answer

Convection

Question 16

The Stefan-Boltzmann law describes the power radiated by an object. Which equation represents this law?

Accepted Answer

$$\frac{Q}{t} = \sigma \epsilon A T^4$

Question 17

A black surface has an emissivity of 1. What does this imply about its ability to emit radiation?

Accepted Answer

It is a perfect emitter of radiation.

Question 18

For an adiabatic process in an ideal gas, which relationship between pressure and volume holds?

Accepted Answer

$$PV^\gamma = 	ext{const}$$

Question 19

In the context of molar specific heat for an ideal gas, what is the relationship between $$C_p$$ and $$C_v$$?

Accepted Answer

$$C_p = C_v + R$$

Question 20

A cube of ice at -8.5°C is placed in an aluminum can with water at 20°C. The final temperature is 17°C. Which statement is true about the energy transfer?

Accepted Answer

The water and aluminum lose heat to the ice, which gains heat.

Thermodynamics: Latent Heat, Laws, and Heat Transfer Mechanisms

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