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Item RG070003: A cold pack has more chemical energy after the salt inside it dissolves. When the salt dissolves, some energy is transferred from the surroundings to the cold pack and converted into chemical energy.

Cold packs are commonly used to treat athletic injuries.  A cold pack contains two chambers. One is filled with water and the other is filled with salt. When the cold pack is squeezed, the chamber containing the salt breaks open, which allows the salt and the water to mix inside the cold pack. As the salt and water mix, the salt dissolves and the temperature of the cold pack decreases.

After the salt has dissolved, does a cold pack have more, less, or the same amount of chemical energy as it does when the salt begins to dissolve? Why?

  1. The cold pack has more chemical energy after the salt has dissolved. When the salt dissolves, some energy is transferred from the surroundings to the cold pack and converted into chemical energy.
  2. The cold pack has less chemical energy after the salt has dissolved because some energy is transferred from the cold pack to the surroundings, which cools the surroundings.
  3. The cold pack has the same amount of chemical energy after the salt has dissolved because even though some energy is transferred from the surroundings to the cold pack, that energy does not affect the amount of chemical energy the cold pack has.
  4. The cold pack has the same amount of chemical energy after the salt has dissolved because no energy is transferred between the surroundings and the cold pack. The cold pack gets colder by absorbing coldness from the surroundings.
Distribution of Responses
Chart showing distrubtion of responses for Item 070003
Scale Score for Item Difficulty
(200[Easy]-800[Difficult])
517
Students Responding Correctly
Group Correct Total Percent
Overall 409 1228 33%
Grades
  4–5N/AN/AN/A
  6–8 221 640 35%
  9–12 188 588 32%
Gender
  Male20559435%
  Female19361032%
Primary Language
  English337104232%
  Other5914940%

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