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 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 reaction. This is because the mass is conserved within the closed system, as stated by the law of conservation of mass. Since the container is sealed, the total mass of the products and remaining reactants inside the container will be equal to the initial mass of the chemical.

Step-by-step solution

Understand the given information

We have a sealed glass container with a chemical placed on a balance. The chemical undergoes a reaction by being ignited. The container is filled with air and has an initial mass of 250.0 g.

Law of Conservation of Mass

According to the law of conservation of mass, the total mass of a closed system remains constant during a chemical reaction. In our case, the glass container is a closed system, as it is sealed and doesn't exchange any mass with the surroundings.

Analyze the chemical reaction

When the chemical reacts in the container, it forms new products. Since the container is sealed, these products cannot escape the container. Hence, the total mass of the products and remaining reactants inside the container will be equal to the initial mass of the chemical.

Determine the final reading on the balance

As the total mass of the container remains constant throughout the reaction, the mass measured by the balance at the end of the reaction will be the same as the initial mass, which is 250.0 g.

Final answer

Therefore, the correct option is (b) - The balance will read 250.0 g after the chemical reaction, because the mass is conserved within the closed system.

Key concepts

closed system

Understanding a closed system is crucial when dealing with chemical reactions. A closed system is one where no mass enters or exits, despite being in an environment where changes like temperature or pressure may occur. In the context of the exercise, the sealed glass container represents a closed system. Inside this environment, even when the chemical burns or reacts, no gases or particles can escape or enter from the outside. This ensures that the mass remains constant.
For example, if you were to weigh the contents before and after a reaction takes place within a closed system, you'd find that the total weight is the same. This principle is vital in understanding how reactions progress without any loss of mass. In short, a closed system isolates its contents from external changes.

chemical reaction

A chemical reaction involves transforming substances into different substances. In chemical equations, reactants (substances initially present) are converted to products (substances formed by the reaction). In the exercise, the chemical ignited using sunlight undergoes a reaction, forming new products.
Essential to understanding this is knowing that during a chemical reaction, bonds between atoms are broken and reformed. However, within a sealed environment, as presented in the exercise, nothing is lost to the surroundings.

• The reaction may involve energy changes, like releasing heat during combustion.
• The chemical composition changes, as atoms rearrange to form new molecules.

This essential change showcases the dynamic nature of chemical reactions and their ability to produce different products while conserving mass within a closed system.

balance scale

A balance scale is an instrument used to measure the weight of objects. In scientific experiments involving closed systems and reactions, a balance scale plays a vital role in showing the conservation of mass.
In the exercise, the initial weight of the sealed container was 250.0 g. After the reaction, since it's a closed system, the balance scale reading remains unchanged. This demonstrates that even though a chemical reaction has taken place, the total weight remains the same because the system was closed.
Therefore, the balance scale effectively highlights how mass is neither created nor destroyed within closed systems, a concept rooted deeply in the law of conservation of mass.

sealed container

A sealed container is a key part of ensuring a closed system during a reaction. By preventing the exchange of matter with the environment, sealed containers maintain constant mass even as reactions proceed. In the exercise scenario, the glass container ensures that, while the chemical reacts, nothing escapes or enters.
Sealed containers are used in experiments to ensure accuracy and integrity, making sure that any change in mass is due to internal processes only, not external interference.

• They keep the reaction products contained, which is crucial for studying complete reactions.
• The initial and final mass readings are crucial to confirming the law of conservation of mass.

In essence, without a sealed container, the weight you measure after a reaction can change unpredictably due to interactions with the environment.