Students should grasp the idea quickly, but it's worth practicing the words with them a few times. If you want to make this into a longer activity, I suggest writing each pair of words on the board, and asking students to name things that could go in each category. For example, "fire" and "sun" under "hot", and "snow" and "ice cream" under "cold."
Obviously, answering in English is best, but I advise not sweating it if students don't know a word they want to use in English. Lean on your JTEs there if you don't know the word either.
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