Chapter U5.99, Problem 5E

(a)

Interpretation Introduction

Interpretation :

Whether boiling ethanol is exothermic or not is to be explained.

Concept Introduction :

Any change in matter is accompanied by a change in energy. Many chemical reactions result in products that are hotter or colder than the reactants. Chemists have categorized chemical changes according to heat transfer. Heat is a transfer of energy due to temperature differences. There are two types of chemical changes; endothermic and exothermic changes.

Answer to Problem 5E

Boiling ethanol is not an exothermic process.

Explanation of Solution

When heat is transferred out of the system to the surroundings, the process is called exothermic and when heat is transferred from the surroundings to the system the process is called endothermic.

Boiling ethanol is not an exothermic process because boiling draws heat from the surrounding rather than releasing heat. During boiling energy is going into the substance. All the energy is used to break the intermolecular forces of attraction so that the molecules can move freely as a gas. Hence boiling ethanol is an endothermic process.

(b)

Interpretation Introduction

Interpretation :

Whether freezing liquid mercury is exothermic or not is to be explained.

Concept Introduction :

When a substance changes phase from a solid to a liquid or from a liquid to a gas, a certain amount of energy is transferred to the substance from the surroundings. When a substance changes phase from a gas to a liquid or from a liquid to a solid, a certain amount of energy is transferred from the substance to the surroundings.

Answer to Problem 5E

Freezing liquid mercury is an exothermic process.

Explanation of Solution

When heat is transferred out of the system to the surroundings, the process is called exothermic and when heat is transferred from the surroundings to the system the process is called endothermic.

Freezing liquid mercury is an exothermic process because freezingreleases heat to the surrounding rather than absorbing heat. During freezing or cooling energy is released into the surrounding. Energy is taken away from the molecules and given out to the surroundings so that the particles come closer and have strong intermolecular force of attraction. Hence freezing liquid mercury is an exothermic process.

(c)

Interpretation Introduction

Interpretation :

Whether subliming carbon dioxide is exothermic or not is to be explained.

Concept Introduction :

Any change in matter is accompanied by a change in energy. Many chemical reactions result in products that are hotter or colder than the reactants. Chemists have categorized chemical changes according to heat transfer. Heat is a transfer of energy due to temperature differences. There are two types of chemical changes; endothermic and exothermic changes.

Answer to Problem 5E

Subliming carbon dioxide is not an exothermic process.

Explanation of Solution

When heat is transferred out of the system to the surroundings, the process is called exothermic and when heat is transferred from the surroundings to the system the process is called endothermic.

Subliming carbon dioxide is not an exothermic process because sublimation draws heat from the surrounding rather than releasing heat. During sublimation, the phase changes from solid to gas and so energy is going into the substance. All the energy is used to break the intermolecular forces of attraction so that the molecules can move freely as a gas. Hence subliming carbon dioxide is an endothermic process.