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Which of the following processes are endothermic?

The temperature of water increases from 20°C to 90°C.

Droplets of condensation form on the outside of a window.

Vapor rises off a block of dry ice.
An ice cube melts on a hot sidewalk.

Frost forms on the leaves of a tree.

User Sorceri
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Answer: I think your answer is "Vapor rises off a block of dry ice/An ice cube melts on a hot sidewalk."

Explanation: A good rule of thumb when figuring out whether a reaction is exothermic or endothermic is to consider whether it would be cold to the touch or hot to the touch. Heat usually means exothermic, and cold usually means endothermic.

An endothermic reaction is cold because it absorbs the heat from its surroundings in order to react. This takes the heat energy away and leaves its surroundings cold.

The answer can't be A because the water's rising temperature would let off heat. The answer can't be B because condensation does not make its environment colder. D is a little bit tricky, however, water freezing into frost is exothermic, not endothermic. This may seem counterintuitive because frost is cold, but this is true because when something freezes, it loses heat. Energy can't vanish, so the heat must be released into the environment. Because it technically releases heat, D is exothermic and is not the correct answer.

Summary: Fusion, vaporization, and sublimation are endothermic processes, whereas freezing, condensation, and deposition are exothermic processes.

User LeYAUable
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