Question

$24g$ of carbon reacts with some oxygen to make $88g$ of carbon dioxide. Find out how much oxygen must have been used.

Answer 1

Hint: To solve this question, we must first understand the basic law of conservation of mass. Then we need to assess the given data and use the correct method to calculate the required mass of oxygen used and then only we can conclude the correct answer.


Complete solution:
Before we move forward with the solution of this given question, let us first understand some basic concepts:
We all must know that in physics and chemistry, the law of conservation of mass or principle of mass conservation states that for any system closed to all transfers of matter and energy, the mass of the system must remain constant over time, as the system's mass cannot change, so quantity can neither be added nor be removed. Therefore, the quantity of mass is conserved over time.
Step 1: In this step we will use the given data to calculate required mass of oxygen used in the process:
Given, Amount of carbon used: $24g$
Amount of carbon dioxide formed: $88g$
Since the mass is conserved over a reaction,
And therefore, Mass of Oxygen $ = (\,88 - 24)g = \,$$64g$

And hence the required mass of oxygen is $64g$.


Note:The principle that the mass of a system of particles must be equal to the sum of their rest masses, even though true in classical physics, may be false in special relativity. The reason that rest masses cannot be simply added is that this does not take into account other forms of energy, such as kinetic and potential energy, and massless particles such as photons, all of which may (or may not) affect the total mass of systems.