change in state and thermodynamics

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Multiple Choice

At what point in the heating curve does the temperature of water remain constant while the substance changes from solid to liquid?

• Between points A and B

• Between points B and C

• Between points C and D

• Between points D and E

Open Ended

Describe the process that occurs between points B and C in the heating curve of water, as shown in the diagram.

Multiple Choice

Which of the following terms refers to the amount of energy required to change a solid into a liquid at its melting point?

• Heat of fusion

• Heat of vaporization

• Entropy

• Joule

Open Ended

Explain why the temperature does not increase during the melting and boiling processes, even though thermal energy is being added.

Multiple Select

Which of the following statements are correct about the changes of state as thermal energy is added to water?

• The temperature increases steadily during melting.

• The temperature remains constant during the phase change from solid to liquid.

• The heat of fusion is the energy required to melt ice at constant temperature.

• The temperature increases steadily during vaporization.

Multiple Choice

What does the horizontal segment between points D and E on the temperature vs. heat graph represent?

• The heat of fusion

• The heat of vaporization

• The specific heat of water

• The specific heat of ice

Multiple Choice

Which of the following statements is true about the heat of fusion?

• It is the energy needed to vaporize 1 kg of a substance.

• It is the energy needed to melt 1 kg of a substance.

• It is the energy needed to heat 1 kg of steam.

• It is the energy needed to freeze 1 kg of a substance.

Multiple Select

Which of the following statements about the heat required to vaporize or freeze a substance are correct?

• The heat required to vaporize a liquid is given by Q = mHv.

• The heat required to freeze a liquid is given by Q = -mHf.

• The negative sign indicates heat is added to the sample.

• The heat required to condense a vapor is given by Q = -mHv.

Multiple Choice

What is the total amount of heat needed to melt 1.50 kg of snow at 0.0°C and heat it to 70.0°C?

• 9.40 × 10^2 kJ

• 5.01 × 10^2 kJ

• 4.39 × 10^2 kJ

• 3.34 × 10^5 J

Multiple Choice

According to the first law of thermodynamics, what is the correct relationship between the change in thermal energy (ΔU), heat (Q), and work (W)?

• ΔU = Q - W

• ΔU = Q + W

• ΔU = W - Q

• ΔU = Q × W

🧊 First Law of Thermodynamics

Energy can't be created or destroyed—only changed.

• Think of it like your phone battery: charging it adds energy, using it drains energy, but the total energy is just moving around.

• Formula:

ΔU=Q−W\Delta U = Q - W

(Change in thermal energy = heat added – work done)

• Real-life activity: Rub your hands together. They get warm because you're turning mechanical energy (motion) into thermal energy (heat)!

• Heat engine (like a car): Converts fuel (thermal energy) into motion (mechanical energy), but always loses some heat.

• Refrigerator: Uses electricity (mechanical work) to move heat from inside (cold) to outside (warm)—against nature’s flow!

Multiple Select

Which of the following statements are true about the first law of thermodynamics?

• It is a restatement of the law of conservation of energy.

• It states that energy can be changed into other forms.

• It states that energy can be created or destroyed.

• It involves the study of changes in the thermal properties of matter.

Multiple Choice

In the context of a heat engine, what happens to the heat from the engine when an automobile is functioning?

• It is transferred to the outside air and the radiator.

• It is completely converted into work.

• It is absorbed by the cold reservoir only.

• It remains within the engine.

Multiple Choice

Which of the following statements best describes why even the most efficient engines cannot reach 100 percent efficiency according to the first law of thermodynamics?

• Because some energy is always lost as waste heat that cannot be converted into work.

• Because engines are not built with perfect materials.

• Because the input heat is always less than the output work.

• Because the internal energy of the engine always increases.

Multiple Choice

According to the first law of thermodynamics, what is the relationship between the heat removed from the refrigerator’s contents, the work done by the motor, and the heat expelled?

• The sum of the heat removed and the work done equals the heat expelled.

• The heat removed is equal to the work done by the motor.

• The heat expelled is less than the heat removed.

• The work done by the motor is equal to the heat expelled.

Multiple Choice

Which of the following statements about heat pumps is correct?

• In the summer, a heat pump removes heat from a house to cool it.

• In the winter, a heat pump removes heat from a house to cool it.

• A heat pump does not require mechanical energy to transfer heat.

• A heat pump can only operate in one direction.

Second Law of Thermodynamics

Heat flows naturally from hot to cold, and things tend to get messier (more disordered).

• Imagine putting a hot spoon in cold water. The spoon cools down, the water warms up—heat spreads out.

• This spreading out is called entropy—a measure of disorder.

💡 Real-life activity: Put an ice cube in warm water. Watch how it melts and cools the water. That’s heat moving from warm to cold, increasing entropy!
the more heat you add at a lower temperature, the greater the increase in entropy.

Your image is ready now! It shows two rooms:

• Left side: A neat, organized room = Low entropy

• Right side: A messy, scattered room = High entropy

Multiple Select

Which of the following statements about entropy is/are correct?

• If heat is added to an object, entropy increases.

• If heat is removed from an object, entropy decreases.

• The change in entropy is given by ΔS = Q/T.

• Entropy has units of J/K.

Multiple Choice

Which of the following best describes what happens when thermal energy is transferred to a substance?

• Energy is conserved and entropy does not spontaneously decrease.

• Energy is destroyed and entropy increases.

• Energy is created and entropy decreases.

• Energy is lost and entropy remains constant.