Problem 54 - Chemistry Matter and Change

Question

Copper sulfide is formed when copper and sulfur are heated together. In this reaction, 127 g of copper reacts with 41 g of sulfur. After the reaction is complete, 9 g of sulfur remains unreacted. What is the mass of copper sulfide formed?

Step-by-Step Solution

Answer

The mass of copper sulfide formed is 159 g, which is obtained by first calculating the mass of reacted sulfur (32 g) and then adding the mass of copper (127 g).

Step 1: Find the mass of sulfur that reacted

We are given that 9 g of sulfur remains unreacted, and the total mass of sulfur before the reaction was 41 g. Therefore, the mass of reacted sulfur is the initial mass of sulfur minus the unreacted mass: \(m_{reacted\,sulfur} = m_{initial\,sulfur} - m_{unreacted\,sulfur}\). Now, plug in the given values and calculate the mass of reacted sulfur: \(m_{reacted\,sulfur} = 41\,g - 9\,g = 32\,g\).

Step 2: Find the mass of copper sulfide formed

The mass of copper sulfide formed can be found by adding the mass of copper and the mass of the reacted sulfur: \(m_{copper\,sulfide} = m_{copper} + m_{reacted\,sulfur}\). Now, plug in the given mass of copper and calculated mass of reacted sulfur: \(m_{copper\,sulfide} = 127\,g + 32\,g = 159\,g\). So, the mass of copper sulfide formed is 159 g.

Key Concepts

Stoichiometry

Stoichiometry is all about calculating the amounts of reactants and products in chemical reactions. It helps you understand how much of each substance is needed or produced. This involves using ratios from balanced chemical equations. For example, if you know the amounts of copper and sulfur reacting, stoichiometry lets you calculate the quantity of copper sulfide formed.

• It uses molar ratios derived from balanced chemical equations.
• Helps in calculating mass, volume, and moles of substances.
• Ensures the right proportions of reactants are used in reactions.

This is important because if the wrong amounts are used, it could lead to incomplete reactions or waste. In the copper sulfide reaction, we use stoichiometry to determine how much sulfur reacts with copper to form the compound.

Chemical Reactions

A chemical reaction transforms reactants into products. In the case of copper sulfide, copper and sulfur come together when heated to form a new substance, copper sulfide. This involves breaking and forming chemical bonds.

• Chemical reactions involve rearrangement of atoms.
• New products are formed with different properties from reactants.
• Energy changes often occur, such as heat absorption or release.

Understanding chemical reactions helps us predict how substances will behave when mixed and what new substances will form. Here, the combination of copper and sulfur forms a stable compound, demonstrating how reactions can create new materials.

Mass Conservation

Mass conservation, or the law of conservation of mass, states that mass is neither created nor destroyed in a chemical reaction. This means the total mass of reactants equals the total mass of products. In the context of forming copper sulfide:

• Total mass before reaction = Total mass after reaction.
• Ensures that calculations based on this principle are accurate.
• Useful for verifying chemical equations and stoichiometric calculations.

In our problem, the mass of copper and the reacted sulfur (159 g) equals the mass of the copper sulfide formed. This reflects mass conservation, ensuring that all matter is accounted for in the reaction.

Copper and Sulfur

Copper and sulfur are the two reactants in the formation of copper sulfide. Copper is a reddish-brown metal known for its conductivity, whereas sulfur is a yellow non-metal often found in nature. When combined:

• Copper reacts with sulfur to form copper sulfide (\(Cu + S \rightarrow CuS\)).
• This reaction typically requires heat.
• The product, copper sulfide, is a compound with properties distinct from copper and sulfur.

The unique properties of copper and sulfur contribute to their reactivity, allowing them to form a stable new compound. This process highlights how different materials can combine to form entirely different substances with unique characteristics.

Reaction Completeness

A complete reaction happens when all reactants are consumed to form products. Incomplete reactions leave some reactants unreacted. For copper sulfide formation:

• The goal is for all the copper to react with sulfur.
• Understanding reaction completeness helps optimize materials used.
• This can prevent unreacted waste and ensure efficient production of desired products.

In the exercise, some sulfur remains unreacted, indicating the reaction wasn't complete with respect to sulfur. This is a common situation in chemical reactions and can be adjusted by changing the amounts of reactants or reaction conditions. Recognizing and addressing reaction completeness is crucial in both laboratory and industrial settings.