Q: How many kilojoules are required to melt 32.0 g of ice at 0°C? (Heat of fusion for water = 334 J/g)

$$32.0 \times 334 \div 1000 = 10.7 kJ$$

Q: During condensation of steam at 100°C, how much energy is released when 50.0 g of steam condenses? (Heat of vaporization = 2260 J/g)

$$50.0 \times 2260 \div 1000 = 113 kJ$$

Q: A 175 g sample of steam at 100°C condenses, cools, and freezes to snow at 0°C. Calculate the total energy released. (Heat of vaporization = 2260 J/g, specific heat of water = 4.184 J/g°C, heat of fusion = 334 J/g)

$$175 \times 2260 \div 1000 + 175 \times 100 \times 4.184 \div 1000 + 175 \times 334 \div 1000 = 528 kJ$$

Q: Which equation would you use to calculate the energy required to vaporize a given mass of water?

$$\text{Heat} = \text{mass} \times \text{heat of vaporization}$$

Question 1

Which of the following best describes what occurs during the melting of ice at 0°C?

Accepted Answer

Water molecules absorb energy and transition from a solid to a liquid at a constant temperature.

Question 2

What is the heat of fusion for water, and how is it used in calculations?

Accepted Answer

The heat of fusion for water is 80 cal/g (334 J/g), used to calculate the energy needed to melt or freeze 1 g of water at 0°C.

Question 3

How many kilojoules are required to melt 32.0 g of ice at 0°C? (Heat of fusion for water = 334 J/g)

Accepted Answer

$$32.0 	imes 334 \div 1000 = 10.7 kJ$$

Question 4

Which process describes the direct conversion of a solid to a gas without passing through the liquid phase?

Accepted Answer

Sublimation

Question 5

During condensation of steam at 100°C, how much energy is released when 50.0 g of steam condenses? (Heat of vaporization = 2260 J/g)

Accepted Answer

$$50.0 	imes 2260 \div 1000 = 113 kJ$$

Question 6

Which of the following statements about heating and cooling curves is correct?

Accepted Answer

A plateau (horizontal line) represents a change of state at constant temperature.

Question 7

What is the heat of vaporization for water, and what does it represent?

Accepted Answer

540 cal/g (2260 J/g); the energy required to convert 1 g of liquid water to gas at 100°C.

Question 8

A 175 g sample of steam at 100°C condenses, cools, and freezes to snow at 0°C. Calculate the total energy released. (Heat of vaporization = 2260 J/g, specific heat of water = 4.184 J/g°C, heat of fusion = 334 J/g)

Accepted Answer

$$175 	imes 2260 \div 1000 + 175 	imes 100 	imes 4.184 \div 1000 + 175 	imes 334 \div 1000 = 528 kJ$$

Question 9

Which of the following is true about the boiling point of water?

Accepted Answer

It is the temperature at which water molecules have enough energy to overcome intermolecular forces and become a gas.

Question 10

At what temperature does water condense during cooling, according to the cooling curve?

Accepted Answer

100°C

Question 11

Which equation would you use to calculate the energy required to vaporize a given mass of water?

Accepted Answer

$$	ext{Heat} = 	ext{mass} 	imes 	ext{heat of vaporization}$$

Question 12

Which process is the reverse of sublimation?

Accepted Answer

Deposition

Question 13

If 100 g of liquid water at 0°C is frozen, how much energy is released? (Heat of fusion = 334 J/g)

Accepted Answer

$$100 	imes 334 = 33,400 J$$

Question 14

Which of the following is NOT a change of state?

Accepted Answer

Heating

Question 15

During which process is heat removed from water?

Accepted Answer

Freezing

Question 16

Which of the following best describes what happens at the plateau of a heating curve for water?

Accepted Answer

The substance undergoes a change of state at constant temperature.

Question 17

What is the specific heat of water, and what does it represent?

Accepted Answer

4.184 J/g°C; the energy required to raise the temperature of 1 g of water by 1°C.

Question 18

Which of the following is true about the reversibility of changes of state?

Accepted Answer

Boiling and condensation are reversible processes.

Question 19

A sloped line on a heating curve represents:

Accepted Answer

A temperature change within a single phase.

Chapter 3: Matter and Energy – Changes of State and Associated Energy Calculations

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