Multiple Choice
Which of the following best describes the process of freezing water, and how can you tell?
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8. Thermochemistry
Endothermic & Exothermic Reactions
Multiple Choice
Which of the following processes is endothermic?
A
Neutralization of hydrochloric acid with sodium hydroxide
B
Melting of ice
C
Combustion of methane
D
Condensation of water vapor
Verified step by step guidance1
Understand the definition of an endothermic process: it is a process that absorbs heat from the surroundings, meaning heat energy is taken in during the process.
Analyze each given process in terms of heat flow:
- Neutralization of hydrochloric acid with sodium hydroxide is an acid-base reaction that typically releases heat, so it is exothermic.
- Melting of ice involves changing solid water to liquid water, which requires energy input to break the hydrogen bonds, so it absorbs heat and is endothermic.
- Combustion of methane is a chemical reaction that releases energy in the form of heat and light, so it is exothermic.
- Condensation of water vapor is the process of gas turning into liquid, which releases heat to the surroundings, so it is exothermic.
Identify the process that requires heat absorption (endothermic): melting of ice fits this description because it requires heat to overcome the forces holding the solid structure together.
Conclude that among the options, the melting of ice is the endothermic process because it absorbs heat, while the others release heat.
Remember that phase changes from solid to liquid or liquid to gas are generally endothermic, while the reverse phase changes and combustion reactions are exothermic.
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