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CHE 105/110 Introduction to Chemistry - Exercises and Answers

Phase Transitions: Melting, Boiling, and Subliming

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QUESTION ANSWER

1.

What is the difference between melting and solidification?

1.

Melting is the phase change from a solid to a liquid, whereas solidification is the phase change from a liquid to a solid.

3.

Describe the molecular changes when a solid becomes a liquid.

3.

The molecules have enough energy to move about each other but not enough to completely separate from each other.

5.

What is the energy change when 78.0 g of Hg melt at −38.8°C?

5.

890 J

7.

What is the energy change when 111 g of Br2 boil at 59.5°C?

7.

10.7 kJ

9.

Each of the following statements is incorrect. Rewrite them so they are correct.

  1. Temperature changes during a phase change.
  2. The process of a liquid becoming a gas is called sublimation.

9.

  1. Temperature does not change during a phase change.
  2. The process of a liquid becoming a gas is called boiling; the process of a solid becoming a gas is called sublimation.

11.

Write the chemical equation for the melting of elemental sodium.

11.

Na(s) → Na(ℓ)

13.

Write the chemical equation for the sublimation of CO2.

13.

CO2(s) → CO2(g)

15.

What is the ΔHsub of H2O? (Hint: see Table 3.2 "Enthalpies of Fusion for Various Substances" and Table 3.3 "Enthalpies of Vaporization for Various Substances".)

15.

46.69 kJ/mol

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