Question

Write a balanced equation for each of the following combination reactions: (a) Sulfur is heated with oxygen to form sulfur dioxide gas. (b) Sulfur is heated with oxygen and Pt catalyst to form sulfur trioxide gas.

Short answer

(a) \( S + O_2 \rightarrow SO_2 \); (b) \( 2S + 3O_2 \rightarrow 2SO_3 \).

Step-by-step solution

Identify Reactants and Products

For part (a), the reactants are sulfur (S) and oxygen (O₂), and the product is sulfur dioxide (SO₂). For part (b), the reactants include sulfur (S), oxygen (O₂), and a catalyst (Pt) which does not participate directly in the balanced equation. The product here is sulfur trioxide (SO₃).

Write Initial Chemical Equations

Write the skeleton equations using the identified reactants and products. For (a), the equation is \( S + O_2 \rightarrow SO_2 \). For (b), the equation is \( S + O_2 \rightarrow SO_3 \). Catalysts are not included in the balanced equations.

Balance Each Equation

Ensure that the number of atoms of each element is equal on both sides of the equation. For (a), \( S + O_2 \rightarrow SO_2 \) is already balanced. For (b), balance sulfur and oxygen: \( 2S + 3O_2 \rightarrow 2SO_3 \) to ensure both sides have 2 sulfurs and 6 oxygens.

Key concepts

Reaction Balancing

Balancing chemical reactions ensures that the same number of each type of atom appears on both sides of the equation. This conservation of atoms aligns with the Law of Conservation of Mass. Imagine if these reactions were a seesaw: both sides must be equal for it to be balanced. Start by counting the atoms for each element in the reactants and products. Compare these numbers. If a discrepancy exists, adjust the coefficients, the numbers in front of the formulas, never the subscripts, to balance the equation.
For example, in the reaction of sulfur and oxygen to form sulfur dioxide, the skeleton equation is:

• \( S + O_2 \rightarrow SO_2 \)

Here, the atoms are already balanced, meaning there's one sulfur and two oxygens on both sides. But for the production of sulfur trioxide, the challenge is balancing the numbers of sulfur and oxygen atoms:

• \( S + O_2 \rightarrow SO_3 \)

Initial counting shows a shortage. By placing proper coefficients, we balance the equation:

• \( 2S + 3O_2 \rightarrow 2SO_3 \)

Now, both sides match, with 2 sulfur and 6 oxygen atoms each. This balanced equation reflects reality accurately.

Combination Reactions

Combination reactions are a type of chemical reaction where two or more substances unite to form a single product. These reactions are fundamental as they illustrate the idea of synthesis in chemistry. It's like baking a cake: multiple ingredients come together to form something new.
The exercise involves combination reactions where sulfur combines with oxygen. For part (a), sulfur (\( \text{S} \)) and oxygen (\( \text{O}_2 \)) join to produce sulfur dioxide (\( \text{SO}_2 \)). It's a direct combination, also known as synthesis, resulting in a more complex product from simpler reactants.
In part (b), the presence of a platinum (\( \text{Pt} \)) catalyst helps accelerate the reaction without being consumed. The reaction combines sulfur and oxygen to form sulfur trioxide (\( \text{SO}_3 \)). The catalyst's role is crucial but doesn't appear in the chemical equation, as it's not a direct reactant or product. Combination reactions illustrate the predictable changes substances can undergo when heated or mixed.

Chemical Equations

Chemical equations are symbolic representations of chemical reactions standing as the primary language of chemistry. They show what substances react and form, including states of matter when appropriate. Think of them as a recipe detailing the necessary ingredients and the resultant dish. They not only reveal the reactants and products but also display the stoichiometry of the reaction — the proportional relationship of the ingredients.
Typically, an equation consists of formulas for the reactants on the left, an arrow pointing to the products on the right, like:

• \( \text{Reactants} \rightarrow \text{Products} \)

For example, in the formation of sulfur dioxide:

• \( \text{S} + \text{O}_2 \rightarrow \text{SO}_2 \)

This setup highlights the transformation of elements and bonds. Understanding these symbolic equations allows chemists to predict reaction outcomes and the quantities involved, making them essential tools in the study and practice of chemistry. In exercises like these, recognizing and interpreting the skeleton and balanced equations fortifies students' grasp of how atoms rearrange during reactions.