Chapter 6, Problem 1RQ

Review Question 6.1 When you burn a log in a fire pit, the mass of wood clearly decreases. How can you define the system so that the mass of the objects in that system remains constant?

To determine

The system in which the mass of objects remains constant when a log is burnt in a fire pit and the mass of wood decreases.

Answer to Problem 1RQ

Solution:

The required system can be the fire pit and its surrounding in which the total mass is conserved.

Explanation of Solution

Introduction:

Mass is an example of a conserved quantity. A conserved quantity remains constant in an isolated system, but if the system is not isolated, the quantity might change.

Explanation:

When a log of wood is burnt, the amount of mass that remains, is the same but the solid wood from the log gets converted into smoke and soot. If all the smoke and other gaseous products of the reaction are collected and weighed then it would be exactly equal to the weight of the wood burnt, along with the oxygen consumed during the reaction. Thus, the law of conservation of mass and energy holds true.

Consider the system as fire pit and its surrounding. The burnt log will produce gaseous products and will consume oxygen, which it will take in from the surroundings. Also, the ash formed will remain in the ash pit. Thus, the mass of wood does decrease but it forms gaseous products, uses oxygen and forms ash. But the mass for the considered system, that is fire pit and its surrounding, always remains constant.

Conclusion:

The mass of the system, when a log is burnt, considering the firepit and its surrounding as the system, remains constant.