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

Antoine Lavoisier, a pivotal figure in chemistry, established the law of Conservation of Mass, which asserts that mass is neither created nor destroyed in a chemical reaction. This principle dictates that the mass of the reactants, the substances before the reaction, must equal the mass of the products, the substances formed as a result. For example, if 100 grams of hydrogen and oxygen react to form water, the resulting water will also weigh 100 grams, illustrating the transformation rather than the loss of mass. This foundational concept not only reinforces the balanced chemical equation but also underpins stoichiometry and solution chemistry, guiding the prediction of product amounts from given reactants. Understanding this law is crucial for grasping further chemical processes and reactions.

Law of Conservation of Mass

In 1789, the French chemist Antoine Wassour, 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 and O2 would be our reactants and those after the arrow, in this case H2O, would be our products.

According to Lavasore, all of the 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 are 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 reactance 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 will 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 says how many grams of water vapor will form if 25 grams of hydrogen gas mixes with 12 grams of oxygen gas. Now apply what we just learned about the law of conservation of mass. This isn't going to be too bad, because remember it says 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 this answer here would be 37 grams of products. Now if we wanted to follow the rules for a significant figures, technically this has three sig figs and this has three sig figs. 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 just 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 enter those particular type 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?

The law of conservation of mass is a fundamental principle in chemistry, stating that mass is neither created nor destroyed in a chemical reaction. This means that the total mass of the reactants, the substances you start with, is equal to the total mass of the products, the substances you end up with, in a closed system. The law was formulated by Antoine Lavoisier in the late 18th century and it laid the foundation for modern chemistry.

In practical terms, when you carry out a chemical reaction in a closed container, you'll find that the mass before and after the reaction remains constant, even though the substances' properties might change significantly. This concept is critical in stoichiometry, which is the calculation of reactants and products in chemical reactions. It helps chemists predict the amounts of substances consumed and produced in a reaction, ensuring that equations are balanced in terms of mass.

What does the law of conservation of mass state?

The law of conservation of mass, also known as the 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 long as it is not added to or taken away from. In other words, the mass of the products in a chemical reaction must equal the mass of the reactants. This principle was first established by Antoine Lavoisier in the late 18th century and is foundational in the field of chemistry.

For example, if you start with 10 grams of hydrogen reacting with 80 grams of oxygen to produce water, you will end up with 90 grams of water. The total mass before and after the reaction remains the same, illustrating the law of conservation of mass. This law is crucial for balancing chemical equations and understanding chemical processes.

Who discovered the law of conservation of mass?

The law of conservation of mass was discovered by Antoine-Laurent de Lavoisier, a French chemist, in the late 18th century. Lavoisier is often referred to as the "Father of Modern Chemistry" due to his significant contributions to the field. Through his experiments, Lavoisier demonstrated that mass is neither created nor destroyed in chemical reactions. Instead, the total mass of the reactants equals the total mass of the products. This principle laid the groundwork for the science of stoichiometry and is a fundamental concept in both chemistry and physics, providing a cornerstone for understanding the conservation of matter in closed systems. Lavoisier's findings were pivotal in discrediting the long-standing phlogiston theory of combustion and in establishing the law of conservation of mass as a fundamental principle of chemistry.