Law of Conservation of Mass: Videos & Practice Problems

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

The law of conservation of mass, established by the French chemist Antoine Lavoisier in the 18th century, is a fundamental principle in chemistry stating that matter cannot be created or destroyed in a chemical reaction. Instead, matter changes form. In a typical chemical reaction, the substances present before the reaction occurs are known as reactants, while the substances formed after the reaction are called products. For example, in the reaction between hydrogen (H₂) and oxygen (O₂) to form water (H₂O), H₂ and O₂ are the reactants, and H₂O is the product.

According to Lavoisier's law, the total mass of the reactants must equal the total mass of the products. If we start with a combined mass of 100 grams of H₂ and O₂, after the reaction, we should also have 100 grams of H₂O. This principle emphasizes that all reactants are transformed into products without any loss of mass, reinforcing the idea that mass is conserved throughout the reaction process.

This concept is crucial for understanding stoichiometry, which involves calculating the quantities of reactants and products in chemical reactions. By applying the law of conservation of mass, chemists can predict the amount of product that can be formed from given amounts of reactants, making it an essential tool in both theoretical and practical chemistry.

Law of Conservation of Mass Example

To determine the amount of water vapor produced from the reaction of hydrogen and oxygen gases, we can apply the law of conservation of mass. This law states that the total mass of reactants must equal the total mass of products in a chemical reaction.

In this scenario, we have 25 grams of hydrogen gas and 12 grams of oxygen gas. By adding these masses together, we find the total mass of the reactants:

Total mass of reactants = 25 g (H₂) + 12 g (O₂) = 37 g

This total mass represents the maximum potential mass of products that can form, which in this case is water vapor (H₂O). Therefore, the total mass of water vapor produced will also be 37 grams.

When considering significant figures, both the hydrogen and oxygen measurements have three significant figures. Thus, the final answer should be expressed as 37.0 grams of water vapor, indicating precision in the measurement.

It's important to note that while the law of conservation of mass holds true in this basic calculation, more complex chemical reactions may involve additional factors that could affect mass balance. In such cases, advanced calculations and concepts will be necessary to accurately determine the outcomes.

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

Answer: (A)

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

Answer: (B)

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.