How does a balanced chemical equation show that mass is never ...

Question

How does a balanced chemical equation show that mass is never lost or gained in a chemical reaction?

Accepted Answer

Welcome back everyone. Which fundamental principle requires chemical equations to be balanced. Choice A states the law of definite composition choice B states the law of definite proportions. Choice C is the law of multiple proportions. And choice D is the law of conservation of mass. Recall that when balancing chemical equations, we should one have equal number of atoms on the reactant and product side. So on both sides of the reaction two, we need to make sure that only the coefficients change, not the reactant or product identity, which is going to be defined by any subscripts. And then three, we want to make sure that no matter is created nor destroyed. And number three is very important because that shows that we would obey the law of conservation of mass. So looking at our answer choices, choice A, the law of definite composition recall describes the fact that a compound always contains the same elements in the same fixed proportions by mass. Recall that the law of definite composition is also known as the law of definite proportion. So choices A and B are the same and they're just different ways of naming the law an example of these two laws or of this law is in consideration of the substance water where no matter the source, whether it's from a laboratory, a river or a well, the proportions of oxygen to hydrogen, we'll say the proportions of the elements by mass are the same. And that will be true whether we have a tiny droplet of water or a large quantity. Now, this law is not a fundamental principle for balancing chemical equations. And so we can rule out choices A and B for that reason. Then we have choice C the law of multiple proportions, which recall describes that when elements combine to form multiple compounds, the ratio of the masses of one element combining with the fixed mass of another element are in small hole number ratios. So let's think of an example to describe that. Let's think of the elements, carbon and oxygen which can combine to form two different compounds, they can form carbon monoxide or let's say carbon dioxide CO2, I'm sorry. That's CO recall the mass of carbon which is 12 g and oxygen which is g. So in carbon monoxide, 12 g of carbon is combined with g of oxygen. Whereas in carbon dioxide, 12 g of carbon is combined with 32 g of oxygen. So we can summarize that for a fixed max of carbon, 12 g, the masses of oxygen that can combine with it are in a ratio of 16 to and note that this ratio can simplify to just 1 to 2 as a simple whole number ratio. And that is consistent with the law of multiple proportions. So for that reason, we can understand that this has nothing to do with balancing a chemical equation. And we would rule out choice C for that reason. And then we have choice d the law of conservation of mass, as we stated, when balancing a chemical equation, no matter should be created nor destroyed. And so that is in direct obedience of the law of conservation of mass, which is why it's important that there are equal number of atoms on both sides of the reaction. And that only the coefficients change and not the subscripts for the reactants are products which would maintain their identity if those do not change. And so choice D would be the only fundamental principle required to balance chemical equations, which is the law of conservation of mass. I hope that this made sense and let us know if you have any questions.

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How does a balanced chemical equation show that mass is never lost or gained in a chemical reaction?

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