Here is the first experiment we had that day. More specifically, it was a teacher demonstration.
Basically, iodine crystals were placed in a round-bottomed flask, which was then gently heated. When the crystals were heated, they sublimed to form purple gas. Later, the flask was cooled and the purple fumes were deposited on the side, forming a solid again.
Then, we did another experiment, this time we did it by ourselves. We were made to heat two different substances, the first one is Sodium Chloride, the second one was Copper (II) Carbonate. When heated, the Sodium Chloride melted into liquid, whereas the Copper (II) Carbonate turned into the colour black upon heating. After leaving them to cool down for a while, the Sodium Chloride solidified, whereas there was no observable change for the Copper (II) Carbonate, meaning it still looked black after cooling.
We then realised that the formal change was a physical change, because the substance went through a change of state, from solid to liquid, and then liquid to solid. Likewise, the Iodine crystals also went through a change of state, sublimation (solid to gas), thus it is a physical change too. However, the latter change is a chemical change, because the change is irreversible, which means that the Copper (II) Carbonate cannot be changed back to its original green colour. When the Copper (II) Carbonate was heated, a chemical reaction took place. The following word equation will show what happens when it is heated:
Copper (II) Carbonate --> Copper (II) Oxide + Carbon Dioxide
Since another substance is produced after heating the Copper (II) Carbonate, we can see that the latter change is a chemical change.
From this lesson and experiment, I learnt what makes up a physical change and what makes up a chemical change. A physical change is the change of state, and it is a reversible process. However, a new substance is produced during a chemical change, and the process is irreversible.
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