For Grade 9A ๐ฟ๐ง. ๐ฟ๐ช๐๐ showed the students 2 examples for chemical reaction using two experiments. The first one was (๐ฉ๐๐ ๐๐ก๐๐ฅ๐๐๐ฃ๐ฉโ๐จ ๐ฉ๐ค๐ค๐ฉ๐๐ฅ๐๐จ๐ฉ๐), it is an example of exothermic reaction and gas production, the 2nd experiment was about color change and the change of state of matter. By using solid iodine, the students had the unique opportunity to observe the change of color from silver to purple as a clue for chemical reaction.