Question

Write a balanced equation for each of the following combination reactions: (a) Copper is heated with chlorine gas to produce solid copper(I) chloride. (b) Cobalt is heated with sulfur powder to produce solid cobalt(II) sulfide.

Short answer

(a) \(2Cu + Cl_2 \rightarrow 2CuCl\); (b) \(Co + S \rightarrow CoS\).

Step-by-step solution

Identify Reactants and Products (a)

In part (a), the reactants are copper (Cu) and chlorine gas (Cl₂), while the product is copper(I) chloride (CuCl). This is a combination reaction where two reactants combine to form a single product.

Write Unbalanced Equation (a)

For part (a), the unbalanced equation based on the identified reactants and products is: \[Cu + Cl_2 ightarrow CuCl\]

Balance the Equation (a)

To balance the equation, note that there are 2 chlorine atoms in Cl₂. We need 2 copper(I) chloride molecules to ensure all chlorine atoms are used, so adjust copper accordingly: \[2Cu + Cl_2 ightarrow 2CuCl\]

Identify Reactants and Products (b)

In part (b), the reactants are cobalt (Co) and sulfur powder (S), and the product is cobalt(II) sulfide (CoS). This is also a combination reaction.

Write Unbalanced Equation (b)

For part (b), write the unbalanced equation based on the reactants and products: \[Co + S ightarrow CoS\]

Balance the Equation (b)

In the equation for part (b), the atoms are already balanced, as there is one cobalt, one sulfur on each side, producing: \[Co + S ightarrow CoS\]

Key concepts

Balanced Equations

In chemistry, a balanced equation is essential to accurately represent a chemical reaction. A balanced chemical equation ensures that the number of each type of atom on the reactant side (left) equals the number on the product side (right). This concept stems from the Law of Conservation of Mass, which states that mass cannot be created or destroyed in a chemical reaction. Rather, atoms are simply rearranged.

To balance an equation, follow these steps:

• First, write the unbalanced equation based on the reactants and products, keeping correct chemical formulas in mind.
• Count the number of atoms for each element in reactants and products.
• Adjust coefficients (numbers in front of molecules) to match the numbers of all atoms on both sides of the equation.

Remember, subscripts (small numbers in chemical formulas) should not be altered, as they are part of the compound's identity. Manipulating coefficients is the only correct way to balance an equation.
For example, when balancing the reaction of copper with chlorine to form copper(I) chloride, the balanced equation is \[2Cu + Cl_2 \rightarrow 2CuCl\] This equation shows two atoms of copper reacting with a diatomic molecule of chlorine to produce two units of copper(I) chloride, balancing both copper and chlorine atoms.

Combination Reactions

Combination reactions are a type of chemical reaction where two or more substances combine to form a single product. These are among the simplest and most straightforward types of chemical reactions, often easy to visualize.

This reaction type is represented generally as: \[A + B \rightarrow AB\] where two reactants, A and B, form one product, AB. Combination reactions are common in real-world applications, such as synthesizing compounds in industrial processes or biological formations.

• An example is the reaction between copper (Cu) and chlorine gas (Cl₂) to form copper(I) chloride (CuCl). Two substances combine to yield a new, single compound.
• Another example is cobalt (Co) reacting with sulfur (S) to create cobalt(II) sulfide (CoS), demonstrating how elements can unite to form stable compounds.

These reactions are essential in understanding how complex materials develop from simpler ones in nature and manufacturing. They underline the transformative power of chemical reactions.

Chemical Equations

A chemical equation is a symbolic representation of a chemical reaction. It presents the reactants on the left side, products on the right, connected by an arrow (\(\rightarrow\)) pointing towards the products. Chemical equations reveal important details:

• Name and formula of each substance involved
• State of each compound (solid, liquid, gas, or aqueous solution) usually noted in parentheses
• The quantitative relationship between reactants and products

Writing a chemical equation involves determining not only the molecular formulas but also ensuring that it obeys chemical laws, like the Law of Conservation of Mass.
To correctly represent a chemical reaction:

• Identify the reactants and products in their standard formulas.
• Write an initial equation with chemical formulas.
• Adjust coefficients to balance the atoms on both sides of the equation, ensuring compliance with conservation laws.

For instance, the chemical reactions of copper and chlorine gas in forming copper(I) chloride and cobalt with sulfur forming cobalt(II) sulfide are written as chemical equations to reflect their quantitative and qualitative nature. Such equations are vital tools for chemists to predict how reactions proceed and the quantities of materials involved.