Chapter 3, Problem 3.75P

Interpretation Introduction

Interpretation:

The mass of chlorine gas in grams which react completely with $455\text{ g}$ of phosphorous to produce phosphorous pentachloride is to be determined.

Concept introduction:

In a balanced chemical equation, the total mass of reactants and products are equal in a balanced chemical equation, thus, it obeyed the law of conservation of mass. Also, the amounts of substances in a balanced chemical reaction are stoichiometrically equivalent to each other.

Following are the steps to calculate the mass of a chemical substance when the mass of other substance present in the chemical reaction is given.

Step 1: Identify the chemical formulas of the reactants and products. Write the balanced chemical equation.

Step 2: Divide the given mass of the substance by its molar mass to calculate the moles of that compound. The expression to calculate the amount of a chemical substance in moles is as follows:

$\text{Amount}\left(\text{mol}\right)=\frac{\text{Mass }\left(\text{g}\right)}{\text{Molar mass}\left(\text{g/mol}\right)}$ (1)

Step 3: Determine the molar ratio between the substance whose mass is given and the substance whose amount is to be calculated from the balanced chemical equation. Multiply the calculated moles in step 2 by the molar ratio to obtain the amount of the substance.

Step 4: Multiply the amount calculated in step 3 by the molar mass of that substance to calculate the mass. The expression to calculate the mass from the moles of a substance is as follows:

$\text{Mass}\left(\text{g}\right)=\left(\text{Amount}\left(\text{mol}\right)\right)\left(\text{Molar mass}\left(\text{g/mol}\right)\right)$ (2)