In several reactions a colour change indicates the formation of new products. For example, green copper carbonate reacts, when heated, to form black copper oxide and carbon dioxide gas.
在一些反应中颜色会发生变化，它表明产生了新的物质，例如，绿色的碳酸铜在加热时会分解为黑色的氧化铜和二氧化碳气体。
As the copper cools, it shrinks. The black cupric oxide also shrinks. But they shrink at different rates, which makes the black cupric oxide flake off.
由于铜冷却，它缩小。黑色铜氧化物也缩小。但是，他们在不同的收缩率，从而使黑色铜氧化物片赶走。
If you cool it too quickly, the black oxide will stay stuck to the copper.
如果你冷却太快，黑色氧化物将继续坚持铜。
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