Chapter U4.71, Problem 6E

Interpretation Introduction

Interpretation:

A paragraph must be written to convince a friend that mass is conserved when chemical and physical changes take place.

Concept introduction:

Law of conservation of mass states that mass can’t be created or destroyed. Mass can be converted to energy.

Answer to Problem 6E

Total mass is constant before and after a chemical or physical change.

Explanation of Solution

Total mass of the universe is always constant. Changes of matters produces new susbtances with new properties however the total mass of reactants is equal to total mass of products. It is true irrespective of physical or chemical changes. In some cases, mass is reduced. For example, in nuclear reaction, there is mass loss as some amount of mass is converted to binding eneergy of the nucleus which holds together the protons and neutrons.

One chemical reaction is given below where it can be observed that total mass of reactants is equal to total mass of products.

The reaction is as follows:

  $C\left(s\right)+O_2\left(g\right)\to C{O}_2\left(g\right)$

In this reaction 12 g carbon reacted with 32 g oxygen to produce 44 g carbon dioxide. Thus, total mass is same on both sides of the reaction arrow.