Question

You have a chemical in a sealed glass container filled with air. The setup is sitting on a balance as shown below. The chemical is ignited by means of a magnifying glass focusing sunlight on the reactant. After the chemical has completely burned, which of the following is true? Explain your answer. a. The balance will read less than 250.0 g. b. The balance will read 250.0 g. c. The balance will read greater than \(250.0 \mathrm{g}\) d. Cannot be determined without knowing the identity of the chemical.

Short answer

The correct option is (b). The balance will read 250.0 g after the chemical has burned. This is because the sealed glass container is a closed system, and according to the conservation of mass principle, the total mass inside the container will remain constant. Although the composition of the substances inside the container may change due to the chemical reaction, the mass remains constant, and as such, the balance will continue to show 250.0 g.

Step-by-step solution

Understand the conservation of mass principle

The conservation of mass states that, for any closed system, the mass of the system must remain constant over time. In other words, mass cannot be created or destroyed. In this question, the sealed glass container is considered a closed system. Keep in mind that the chemical reaction will not affect the total mass inside the container. II. Apply the conservation of mass principle to the situation

Apply the conservation of mass to the sealed container

As the chemical is burnt, it undergoes a chemical reaction with the air inside the container (assuming the chemical reacts with air). The products formed from this reaction, as well as any unreacted chemicals and air, will still be inside the container as it's sealed. III. Analyze the weight read by balance

Analyze the weight after the reaction

Although the composition of the substances inside the container may change, the total mass will remain constant due to the conservation of mass. The mass inside the container is still 250.0 g, and the balance can only detect the mass, not the type of particles inside. So, the balance will still read 250.0 g after the chemical has burned. Based on our analysis, the correct option is: b. The balance will read 250.0 g.

Key concepts

Closed System

A closed system is one where no matter can enter or leave. In our setup with the sealed glass container, we have an example of such a system. When the chemical inside the container reacts, all the reactants and products of the reaction stay inside. This is because the container is closed, preventing any exchange with the environment outside.

By keeping the container sealed, the mass is conserved during the chemical process. Even though the substances inside may change form or combine in different ways, the total amount of matter remains the same. This means that the conservation of mass principle is directly observable in a closed system.

Chemical Reaction

During a chemical reaction, substances undergo a transformation to form new ones. In the exercise, our chemical reacts when ignited. This process involves the breaking and reforming of bonds between atoms.

When the chemical burns, it likely reacts with the air (in particular, oxygen) inside the container. The result is the formation of new substances, such as gases or other compounds. However, despite the changes in composition, the mass of all substances stays consistent, highlighting the vital principle of mass conservation in the reaction.

Mass Measurement

Mass measurement refers to determining the amount of matter in an object or system. In the context of our sealed container, this measurement is achieved using a balance.

The balance provides an accurate reading of the mass, which in this case is 250.0 grams before and after the chemical reaction. This is because the balance does not differentiate between substances; it only measures total weight. This constancy on the balance confirms the conservation of mass principle, reinforcing that the total mass does not change regardless of chemical transformations within the closed system.

Sealed Container

A sealed container serves as a physical boundary for a closed system. It prevents the exchange of both mass and matter with the external environment.

When the container in our exercise is sealed, all reactants and products stay inside regardless of their state—liquid, solid, or gas. This means that during any reactions occurring in the container, no mass is lost or gained, allowing us to focus solely on the transformations happening within.

This concept is critical for understanding how the conservation of mass applies in a practical, observable manner, ensuring that all matter involved in the reaction is accounted for without escaping or entering the system.