Question

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

Short answer

(a) \(4\text{Li} + \text{O}_2 \rightarrow 2\text{Li}_2\text{O}\); (b) \(2\text{Ca} + \text{O}_2 \rightarrow 2\text{CaO}\).

Step-by-step solution

Identify the Products of the Reaction

Combination reactions involve two or more substances combining to form a single compound. In the given reactions, lithium (Li) and calcium (Ca) are metals reacting with oxygen (O₂). The products will be lithium oxide (Li₂O) and calcium oxide (CaO) respectively.

Write the Unbalanced Chemical Equations

For each reaction, write the chemical equation using the products identified in step 1. (a) For reaction between lithium and oxygen: \[ \text{Li} + \text{O}_2 \rightarrow \text{Li}_2\text{O} \](b) For reaction between calcium and oxygen: \[ \text{Ca} + \text{O}_2 \rightarrow \text{CaO} \]

Balance the Chemical Equations

To satisfy the law of conservation of mass, balance each reaction. (a) Balancing lithium:- There are two lithium atoms in Li₂O, so we need two lithium atoms on the reactant side:\[ 4\text{Li} + \text{O}_2 \rightarrow 2\text{Li}_2\text{O} \](b) Balancing calcium:- Calcium and oxygen are already balanced as there is one calcium atom in CaO and one oxygen molecule (two atoms) in O₂:\[ 2\text{Ca} + \text{O}_2 \rightarrow 2\text{CaO} \]

Key concepts

Combination Reactions

In every day chemistry, combination reactions play a pivotal role in explaining how different substances combine to form a single compound. These reactions, sometimes called synthesis reactions, are characterized by the union of two or more elements or smaller compounds to create a single, more complex product.
A classic example of a combination reaction is when metals like lithium (Li) and calcium (Ca) react with oxygen (). In these scenarios, the metal and oxygen come together, resulting in metal oxides such as lithium oxide (Li2) and calcium oxide (CaO).
Such reactions might seem straightforward, but they help illustrate the underlying principle that new compounds are formed through the rearrangement of atoms. Recognizing and analyzing combination reactions allows us to better predict the outcomes of reactions in the real world.
Important characteristics of these reactions include:

• Formation of a single product from multiple reactants.
• Exothermic nature, meaning they often release heat.
• Commonly involve metals reacting with nonmetals.

Understanding how combination reactions work paves the way for more complex concepts in chemistry, such as understanding industrial processes and biological mechanisms.

Balancing Equations

Balancing chemical equations is crucial for accurately representing chemical reactions. The goal is to ensure that the number of atoms of each element is the same on both sides of the equation, reflecting the reality that matter is neither created nor destroyed during a chemical reaction.
To illustrate, let's consider the reaction of lithium with oxygen to form lithium oxide:

Unbalanced: \[ ext{Li} + ext{O}_2 \rightarrow ext{Li}_2 ext{O} \]

Initially, this equation is unbalanced because there are unequal numbers of lithium and oxygen atoms.For balancing:

• Each side of the equation must reflect the same number of each type of atom.
• Coefficients are adjusted to achieve this balance without altering the chemical identity of the compounds involved.

In the case of lithium and oxygen:
We know:
\[ ext{2Li}_2 ext{O} \] contains four lithium atoms and needs only one oxygen molecule from \( ext{O}_2 \). Thus:

Balanced: \[ 4 ext{Li} + ext{O}_2 \rightarrow 2 ext{Li}_2 ext{O} \]

This balances the lithium atoms at four on both sides, while maintaining balance with oxygen atoms. It perfectly matches the reality dictated by the laws of chemistry.Adopting this methodical approach to balance equations not only satisfies theoretical requirements but is also fundamental to accurately calculating amounts of reactants and products required in real-world applications.

Law of Conservation of Mass

The Law of Conservation of Mass is a fundamental principle stating that mass in an isolated system is neither created nor destroyed by chemical reactions or physical transformations. This enormous concept, first formulated by Antoine Lavoisier, is best observed through the balancing of chemical equations.
When reactions occur, they involve the rearrangement of atoms to form new substances, without any loss of mass. This means the total mass of the reactants equals the total mass of the products.
In the previously discussed reactions between lithium with oxygen and calcium with oxygen:

• For lithium with oxygen:\[ 4 ext{Li} + ext{O}_2 \rightarrow 2 ext{Li}_2 ext{O} \]Reactants: 4 lithium atoms and 1 oxygen molecule.
  Products: 4 lithium atoms and 1 oxygen molecule per 2 lithium oxides.
• For calcium with oxygen:\[ 2 ext{Ca} + ext{O}_2 \rightarrow 2 ext{CaO} \]Reactants: 2 calcium atoms and 1 oxygen molecule.
  Products: 2 calcium atoms and 1 oxygen molecule, as 2 calcium oxides.

The visible result of conserving mass in balanced equations ensures that all atoms present in the reactants are accounted for in the products. This rule is indispensable to scientific calculations and allows chemists to predict reaction outcomes reliably.