Physical or/and Chemical Change: What would happen to Zinc Oxide when you heat it up?? - Science

What would happen to Zinc Oxide (ZnO) when you heat it up??

Today in Science, we will be doing an experiment where we will heat "Zinc Oxide" in scientific terms, "ZnO". We will be investigating and finding out which of the chemical change or physical change category it belongs to.

Equipment/Materials: 

• Sample of ZnO (Zinc Oxide)
• Heat source 
• Scales
• Heatproof container
• Tongs
• Heatproof mat

Hypothesis:

In my opinion, as we heat the zinc oxide, the colour will turn black and will cause to light a fire. If we were to compare this to another object, I would compare it to a cigarette. When you light a cigarette, the filter would burn and turn into ash, the type of reaction would happen to the zinc oxide so I think it will be a result of a chemical change due to the change of its colour and heat is absorbed. 

Method/Steps: 

1. Get a sample of ZnO in an evaporating dish.
2. Weigh the ZnO + the container and record its weight.
3. Heat container with the ZnO on a hot plate.
4. Observe any changes. 
5. Take off heat and place it on the heatproof mat.
6. Wait for it to cool down before observing.
7. Re weigh it.

Result: 

From what we've observed, we saw that the colour changed to yellow but it was not clearly visible. 55 was the weight of the evaporating dish and the powder was 2 grams before. After reweighing it, nothing changed to its weight but the colour changed back to white. 

Conclusion:

There was a big difference between my hypothesis and the experiment result. My hypothesis was it will cause a fire and the colour will change to black but from the experiment itself, the colour did change but it wasn't black, it was yellow. It did not cause a fire but I was surprised when it changed back to its real colour which was white. From this, we know that it was a physical change because the colour changed back to its original colour. This is one of the sign or reason why it's a physical change because it can be done reversed.