Law of Conservation of Mass - Online Tutor, Practice Problems & Exam Prep

Antoine Levasseur established the law of conservation of mass, which states that in a chemical reaction, matter is neither created nor destroyed but transformed. For example, when hydrogen (H₂) and oxygen (O₂) react to form water (H₂O), the total mass of reactants equals the total mass of products. This principle is crucial for understanding stoichiometry and solution chemistry, as it allows for the prediction of product amounts based on initial reactant masses, ensuring that all 100 grams of reactants convert entirely into products.

Law of Conservation of Mass

In 1789, the French chemist, Antoine Lavoisier, who's credited as being another father of chemistry, originated the law of conservation of mass. Now, the law states that in a chemical reaction, no matter is created or destroyed, but instead changes form.

In a chemical reaction, we're going to say that the compounds before the arrow, so in this case H2+O2, would be our reactants, and those after the arrow, in this case, H2O, would be our products. According to Lavoisier, all other reactants are converted to product with nothing lost. So to think about it, we could say that originally at the beginning of the reaction, we have H2 and O2, and we're mixing them together. Their combined amount of both of them together, let's say it's 100 grams. Well, according to the law of conservation of mass, nothing is truly lost. It's just converted from one form to another.

So all 100 grams of my reactants should be converted entirely into product. So at the end, I'd have exactly 100 grams of product. All of this would be gone. All of this has been transformed into H2O. So what this tells me is that if you know the total mass of your reactants in the beginning, then they should equal the total mass of products that you create at the end. So this is an incredibly important idea when it comes to the law of conservation of mass. That'll connect to other ideas later on such as stoichiometry and solution chemistry. So just remember, when it comes to law of conservation of mass, it helps us to determine eventually the amount of product we could potentially form.

Law of Conservation of Mass Example 1

In this example question, it asks how many grams of water vapor will form if 25 grams of hydrogen gas mixes with 12 grams of oxygen gas. Now, applying what we just learned about the law of conservation of mass, this isn't going to be too difficult. Because remember, it states that the mass, the total mass of reactants will equal the total mass of products. Here we have the masses of the reactants which are 25 and 12, so when we add them together, that'll give us the total mass of product that could potentially form. So, the answer here would be 37 grams of products. Now, if we want to follow the rule on the significant figures, technically this has 3 significant figures, and this has 2 significant figures, so the better answer would be 37.0 grams of water vapor, which is just water as a gas. So, just remember, if we're simply applying the law of conservation of mass, just remember the amount of reactants equals the amount of products. Now, later on, when we go into more advanced forms of calculations with chemical reactions, we're going to see that's not always true. In those cases, we'll learn new mechanics and new approaches to answer those particular types of questions.

Following the Law of Conservation of Mass, predict the minimum amount of nitrogen that will react with 50.0 grams of hydrogen to produce 92.5 grams of ammonia.

Nitrogen + Hydrogen → Ammonia

• A. 42.5 g
• B. 45.91 g
• C. 46.25 g
• D. 50.0 g

Predict the amount of oxygen gas that will remain after the reaction of 112.6 grams of calcium with 24.0 grams of oxygen.

• A. 8.5 g
• B. 11.0 g
• C. 18.0 g
• D. 24.0 g

Here’s what students ask on this topic:

What is the law of conservation of mass and who discovered it?

The law of conservation of mass states that in a chemical reaction, matter is neither created nor destroyed but transformed from one form to another. This means the total mass of the reactants equals the total mass of the products. This fundamental principle was discovered by the French chemist Antoine Lavoisier in 1789. Lavoisier's work laid the foundation for modern chemistry by establishing that mass remains constant during chemical reactions, which is crucial for understanding stoichiometry and solution chemistry.

How does the law of conservation of mass apply to chemical reactions?

The law of conservation of mass applies to chemical reactions by ensuring that the total mass of the reactants equals the total mass of the products. For example, when hydrogen (H₂) and oxygen (O₂) react to form water (H₂O), the combined mass of H₂ and O₂ before the reaction will equal the mass of H₂O after the reaction. This principle allows chemists to predict the amounts of products formed from given reactants, which is essential for calculations in stoichiometry and solution chemistry.

Why is the law of conservation of mass important in stoichiometry?

The law of conservation of mass is crucial in stoichiometry because it ensures that the mass of reactants equals the mass of products in a chemical reaction. This principle allows chemists to calculate the exact amounts of reactants needed and predict the amounts of products formed. By knowing the initial masses of reactants, one can use stoichiometric coefficients from balanced chemical equations to determine the mass of each product, ensuring no mass is lost or gained during the reaction.

Can you provide an example of the law of conservation of mass in a chemical reaction?

Sure! Consider the reaction between hydrogen (H₂) and oxygen (O₂) to form water (H₂O). If we start with 4 grams of H₂ and 32 grams of O₂, the total mass of reactants is 36 grams. According to the law of conservation of mass, the mass of the products must also be 36 grams. Therefore, the water produced will have a mass of 36 grams, demonstrating that no mass is lost or gained during the reaction.

How does the law of conservation of mass relate to solution chemistry?

In solution chemistry, the law of conservation of mass ensures that the total mass of solutes and solvents before mixing equals the total mass of the solution after mixing. For example, if you dissolve 10 grams of salt in 90 grams of water, the total mass of the solution will be 100 grams. This principle helps in calculating concentrations, dilutions, and reactions occurring in solutions, ensuring that mass is conserved throughout the process.