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Chapter 18: Problem 45

Which of the following processes are exothermic? Explain your thinking. (A) boiling ethanol (B) freezing liquid mercury (C) subliming carbon dioxide

Short Answer

Expert verified
Freezing liquid mercury is exothermic.

Step by step solution

01

Understanding Exothermic and Endothermic Processes

Exothermic processes release heat to the surroundings. Endothermic processes absorb heat from the surroundings. We will use this information to determine whether the given processes release or absorb heat.
02

Analyzing Each Option

We will evaluate each option to determine whether it is exothermic or endothermic. (A) Boiling ethanol: Boiling is the process of a liquid turning into a gas, which requires heat input to overcome intermolecular forces, making it endothermic. (B) Freezing liquid mercury: Freezing involves a liquid turning into a solid, which releases energy as heat to the surroundings, making it exothermic. (C) Subliming carbon dioxide: Sublimation is the transition of a solid directly to a gas, which requires heat, making it endothermic.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Endothermic Processes
An endothermic process is a fascinating event in which a system absorbs energy from its surroundings in the form of heat. This absorbed heat is used to break intermolecular bonds or overcome forces, leading to a change in the physical state of a substance. For instance, when you boil water, you're witnessing an endothermic process in action. Here, water is absorbing heat energy, allowing the molecules to move faster and break free from the liquid state to become gas.
  • Key Characteristic: Absorbs heat
  • Example: Boiling is a common endothermic process
  • Impact: Results in a temperature decrease in the immediate surroundings
Boiling
Boiling is a specific type of endothermic process where a liquid changes its state to a gas. This happens when the molecules within the liquid gain sufficient energy to overcome atmospheric pressure. The temperature at which this transition occurs is known as the boiling point.
Several factors influence boiling, such as ambient pressure and the nature of the liquid itself. At higher altitudes, where atmospheric pressure is lower, the boiling point decreases, meaning liquids boil at lower temperatures. This is why cooking times can vary depending on your location.
  • Key Process: From liquid to gas
  • Heat Transfer: Absorbs heat
  • Example: Boiling ethanol
Freezing
Freezing is the process in which a liquid turns into a solid. Unlike boiling, freezing is an exothermic process. During freezing, the molecules in a liquid slow down as they lose energy and start to form a fixed structure, which is a solid. Heat is released to the environment during this process. For example, when liquid mercury freezes, it releases heat, solidifying into a solid state.
Freezing points are specific to various substances. Water, for instance, freezes at 0掳C (32掳F) under standard atmospheric conditions. Similar conditions apply to other substances, although their specific freezing points may vary.
  • Key Process: Liquid to solid
  • Heat Transfer: Releases heat
  • Example: Freezing liquid mercury
Sublimation
Sublimation is the unique transition of a substance directly from a solid to a gas, bypassing the liquid phase entirely. This process is endothermic because it requires the absorption of heat to break the bonds that hold particles in a solid formation. A classic example of sublimation is dry ice, or solid carbon dioxide, which transforms directly into gas as it warms.
In sublimation, heat energy absorbed helps particles in a solid overcome the forces holding them together, enabling them to disperse into a gaseous state.
  • Key Process: Solid to gas
  • Heat Transfer: Absorbs heat
  • Example: Subliming carbon dioxide

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Most popular questions from this chapter

In your own words, deifne the word energy.

Explain why a campfire burns out. Explain why the ashes eventually cool to the temperature of the surrounding air.

How many calories of energy do you need to transfer for each of the following changes? a. Raise the temperature of 1 g of water by \(5^{\circ} \mathrm{C}\) . b. Raise the temperature of 2 g of water by \(5^{\circ} \mathrm{C}\) . c. Raise the temperature of 9 g of water by \(35^{\circ} \mathrm{C}\) .

How many calories of energy do you need to transfer for each of the following changes? a. Raise the temperature of 1 \(\mathrm{g}\) of water by \(5^{\circ} \mathrm{C}\) . b. Raise the temperature of 2 \(\mathrm{g}\) of water by \(5^{\circ}\) C. c. Raise the temperature of 9 \(\mathrm{g}\) of water by \(35^{\circ} \mathrm{C}\) .

You mix solid hydrated barium hydroxide, Ba(OH) \(\cdot 8 \mathrm{H}_{2} \mathrm{O}(s),\) and solid ammonium nitrate, \(2 \mathrm{NH}_{4} \mathrm{NO}_{3}(s),\) in a beaker. The reaction is shown here. A small pool of water in contact with the outside of the beaker freezes. $$ \mathrm{Ba}(\mathrm{OH})_{2} \cdot 8 \mathrm{H}_{2} \mathrm{O}(s)+2 \mathrm{NH}_{4} \mathrm{NO}_{3}(s) \longrightarrow 2 \mathrm{NH}_{3}(g)+10 \mathrm{H}_{2} \mathrm{O}(l)+\mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2}(a q) $$ a. List all the substances that are part of the system. b. List at least four objects that are part of the surroundings. c. Which is at a lower temperature: \(\mathrm{NH}_{4} \mathrm{NO}_{3}(s)\) or \(\mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2}(a q)\) ? Explain your thinking. d. What will you feel if you touch the beaker? e. Is the reaction endothermic or exothermic? Explain your thinking. f. What evidence do you have that heat is transferred from the surroundings to the products of the reaction?
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