Question

Which of the following is a sign a chemical reaction has occurred?

A blue liquid is mixed into a yellow liquid, and the mixture turns green.
A piece of metal is placed in water and produces sparks and gas.
A liquid is heated on a hotplate, and bubbles form.
A solid powder is mixed into a liquid and disappears.

Answer 1

Answer:

A blue liquid is mixed into a yellow liquid, and the mixture turns green.

A piece of metal is placed in water and produces sparks and gas.

A liquid is heated on a hotplate, and bubbles form.

Explanation:

A chemical reaction occurs when reactants combine or decompose to form products which have a completely different composition and structure than the reactants. There are certain signs which indicate that a chemical reaction has taken place, the primary indicators include:

1) Formation of a precipitate

2) Formation of bubbles

3) color change

4) change in temperature

Based on the given examples:

1) A blue liquid is mixed into a yellow liquid, and the mixture turns green:

This involves a color change and hence a chemical process

2) A piece of metal is placed in water and produces sparks and gas.

Formation of sparks and gas signify a change in temperature and hence a chemical process

3) A liquid is heated on a hotplate, and bubbles form.

Formation of bubbles are indicate that a chemical reaction has occured

Answer 2

The signs among the the given options that chemical reaction has occurred are;

A blue liquid is mixed into a yellow liquid, and the mixture turns green.

A piece of metal is placed in water and produces sparks and gas.

A liquid is heated on a hotplate, and bubbles form.

• When A blue liquid and yellow liquid is mixed and the resulting mixture turns green, then chemical reaction has taken place since there is a formation of new product

• When a A liquid is heated , and bubbles comes up, the bubbles indicate a chemical reaction.

• When a  piece of metal is placed in water which brings about  sparks and gas production, then chemical reaction has taken place because of the spark

• A chemical reaction can be regarded as one that takes place, when there is a reaction between reactants , these reaction could be combination as well as  or decomposition to form products whereby, theses product contains completely different composition as well as structure than the reactants.

Therefore,  certain signs that gives  indication about chemical reaction that  takes place, could be;

1. When there is precipitate formation.
2. Where the bubbles forms
3. Where there is change in color or  change in temperature

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