# A light green powder is heated in a test tube. A gas is given off, and the solid becomes black. Was the change physical or chemical, and is the green powder an element, a compound, or a mixture?

Jan 18, 2016

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#### Explanation:

The question describes an experiment similar to the decomposition of copper(II) carbonate ($C u C {O}_{3}$) which is when heated in decomposes into carbon dioxide gas ($C {O}_{2}$) and copper(II) oxide ($C u O$) according to the following decomposition reaction:

$\textcolor{g r e e n}{C u C {O}_{3} \left(g\right)} \to \textcolor{g r a y}{C {O}_{2} \left(g\right)} + C u O \left(s\right)$

Therefore, the green substance is a compound and the change is a chemical change since giving off a gas is one of the several indication of a chemical change that include:

1. Gas evolution
2. Formation of a precipitate
3. Evolution of heat
4. Odor
5. Color change
6. etc.

Here is a video on physical and chemical change that describes the aforementioned experiment:

Lab Experiment #2: Physical & Chemical Changes.