Question

Complete and balance each of the following combination reactions: (a) \(\mathrm{Sr}+\mathrm{O}_{2} \rightarrow\) (b) \(\mathrm{Al}+\mathrm{O}_{2} \rightarrow\)

Short answer

(a) \(2\mathrm{Sr} + \mathrm{O}_2 \rightarrow 2\mathrm{SrO}\); (b) \(4\mathrm{Al} + 3\mathrm{O}_2 \rightarrow 2\mathrm{Al}_2\mathrm{O}_3\).

Step-by-step solution

Understand the Problem

In combination reactions, two or more reactants combine to form a compound. Here, both reactions involve a metal reacting with oxygen.

Determine Reactants and Products for (a)

Strontium (Sr) reacts with oxygen (\(\mathrm{O}_2\)) to form strontium oxide (\(\mathrm{SrO}\)). The reaction starts as: \(\mathrm{Sr} + \mathrm{O}_2 \rightarrow \mathrm{SrO}\).

Balance the Reaction for (a)

The unbalanced reaction is \(\mathrm{Sr} + \mathrm{O}_2 \rightarrow \mathrm{SrO}\). To balance it, note that each \(\mathrm{SrO}\) uses one Sr and one O, but \(\mathrm{O}_2\) provides two oxygen atoms. The balanced equation is \(2\mathrm{Sr} + \mathrm{O}_2 \rightarrow 2\mathrm{SrO}\).

Determine Reactants and Products for (b)

Aluminum (Al) reacts with oxygen (\(\mathrm{O}_2\)) to form aluminum oxide (\(\mathrm{Al}_2\mathrm{O}_3)\). The reaction starts as: \(\mathrm{Al} + \mathrm{O}_2 \rightarrow \mathrm{Al}_2\mathrm{O}_3)\).

Balance the Reaction for (b)

The unbalanced reaction is \(\mathrm{Al} + \mathrm{O}_2 \rightarrow \mathrm{Al}_2\mathrm{O}_3)\). Balancing involves ensuring equal numbers of each type of atom on both sides. The balanced equation is \(4\mathrm{Al} + 3\mathrm{O}_2 \rightarrow 2\mathrm{Al}_2\mathrm{O}_3)\).

Key concepts

Combination Reactions

Combination reactions are a type of chemical reaction where two or more substances merge to form one single product. In simpler terms, these reactions bring together elements or compounds into a bigger, often more complex compound. This is why they're sometimes referred to as synthesis reactions.

In our exercise, metals are reacting with oxygen to form metal oxides. Specifically:

• Strontium (Sr) and oxygen (\(\mathrm{O}_2\)) form strontium oxide (\(\mathrm{SrO}\)).
• Aluminum (Al) and oxygen (\(\mathrm{O}_2\)) form aluminum oxide (\(\mathrm{Al}_2\mathrm{O}_3\)).

When elements like metals react with nonmetals, you often get a stable compound, such as an oxide, as seen here. Recognizing these reactions as combination reactions helps us predict and understand how new compounds are formed in chemical processes.

Chemical Reactions

Chemical reactions transform substances into different substances, involving rearrangements of atoms and the breaking and forming of chemical bonds. They're fundamental processes in chemistry that can be grouped into types like combination, decomposition, single displacement, and double displacement reactions.

In the context of the exercise:

• The reaction involves metals, strontium and aluminum, reacting with oxygen.
• These are oxidation reactions, forming metal oxides as the products.

The idea is to end up with the same types of atoms you started with, but in a recombined state, producing a different substance. Balancing these reactions involves making sure each side of the chemical equation has the same number of each kind of atom. If we can balance our atoms, the equation satisfies the law of conservation of mass, which states mass can neither be created nor destroyed in a chemical reaction.

Stoichiometry

Stoichiometry is a critical concept for understanding chemical reactions. It involves calculating the proportions of elements and compounds involved in a chemical reaction. It's about keeping balance much like you would with a budget; you must have the same amount coming in as you have going out.

For example, in balancing the reaction of strontium and oxygen to form strontium oxide, we needed to match the number of atoms on both sides:

• The reaction starts unbalanced as \(\mathrm{Sr} + \mathrm{O}_2 \rightarrow \mathrm{SrO}\)
• By balancing, we ensure two Sr atoms combine with one \(\mathrm{O}_2\) molecule, forming two \(\mathrm{SrO}\) units as \(2 \mathrm{Sr} + \mathrm{O}_2 \rightarrow 2 \mathrm{SrO}\)

Similar balancing is done for the aluminum-oxygen reaction to form aluminum oxide. Understanding stoichiometry helps predict how much of each reactant is necessary and what amount of each product will result. It’s like chemistry's recipe book, making sure everything mixes just right.