Chapter 7.1, Problem 2RQ

(a)

Interpretation Introduction

Interpretation:An example of a chemical reaction where a change in color takes place needs to be given.

Concept Introduction: When one or more chemicals are changed into one or more other chemicals, a chemical reaction takes place. For example, Iron and oxygen combine to form rust.

Answer to Problem 2RQ

Color change during a chemical reaction shows a chemical reaction. A chemical reaction is not always visible by naked eyes,but sometimes it results in an impressive color change.

Explanation of Solution

When two or more substances combine, they form one or more products. These products have different molecular structures from the reactants i.e. they absorb and radiate light in different ways, gives color change during a chemical reaction.

Example-When copper reacts with the oxygen, water and CO₂, a reddish-brown color appears in this reaction.

The reaction is represented as follows:

  $\text{Cu}+{\text{O}}_{\text{2}}+{\text{H}}_{\text{2}}\text{O}+{\text{CO}}_{\text{2}}\to \text{Cu}{\left(\text{OH}\right)}_{\text{2}}+{\text{CuCO}}_{\text{3}}$

(b)

Interpretation Introduction

Interpretation: An example of a chemical reaction where precipitation takes place needs to be given.

Concept Introduction: When one or more chemicals are changed into one or more other chemicals, a chemical reaction takes place.

Answer to Problem 2RQ

In any reaction, reactants form products. When the solubility of a product formed is less than the reactant, then the product precipitates out of the solution as a solid and this solid is known as a Precipitate.

Explanation of Solution

When silver nitrate reacts with sodium chloride, silver chloride will separate as a solid. This showsa precipitation reaction.

The reaction is represented as follows:

  ${\text{AgNO}}_{\text{3}}\left(aq\right)+\text{NaCl}\left(aq\right)\to \text{AgCl}\left(s\right)+{\text{NaNO}}_{\text{3}}\left(aq\right)$

(c)

Interpretation Introduction

Interpretation: An example of a chemical reaction where bubbles formed needs to be given.

Concept Introduction: When one or more chemicals are changed into one or more other chemicals, a chemical reaction takes place.

Answer to Problem 2RQ

Bubbles formation during a chemical reaction shows the release of any gas formed during a chemical reaction.

Explanation of Solution

Electrolysis of water is the decomposition of water into oxygen and hydrogen gas. In an electrolysis reaction, water splits into hydrogen and oxygen molecules. When the current is applied to electrolysis reaction, the electrons on the cathode end will combine with water, and release hydrogen. These hydrogen atoms combinine to form hydrogen bubbles.

The reaction is represented as follows:

  ${\text{H}}_{\text{2}}\text{O}\left(l\right)\to {\text{H}}_{\text{2}}\left(g\right)+{\text{O}}_{\text{2}}\left(g\right)$

(d)

Interpretation Introduction

Interpretation: An example of a chemical reaction where combustion takes place needs to be given.

Concept Introduction: When one or more chemicals are changed into one or more other chemicals, a chemical reaction takes place.

Answer to Problem 2RQ

A combustion reaction is commonly known as burning. A combustion reaction involves a reaction between any combustible materials.

Explanation of Solution

Combustion reaction generally occurs when a hydrocarbon reacts with oxygen and form CO₂ and H₂O.

Example: Combustion of methane is represented as follows:

  ${\text{CH}}_{\text{4}}+{\text{O}}_{\text{2}}\to {\text{CO}}_{\text{2}}+2{\text{H}}_{\text{2}}\text{O}$