Question

For each of the following synthesis reactions, identify the missing reactant(s) or product(s), and then balance the resulting equation. a. \(\mathrm{Mg}+ \)_________ \(\longrightarrow \mathrm{MgO}\) b. _________ \(\mathrm{+} \mathrm{O}_{2} \longrightarrow \mathrm{Fe}_{2} \mathrm{O}_{3}\) c. \(\mathrm{Li}+\mathrm{Cl}_{2} \longrightarrow\) _________ d. \(\mathrm{Ca}+\) _________ \(\longrightarrow \mathrm{CaI}_{2}\)

Short answer

a. \(\text{O}_2\), balanced: \[2 \text{Mg} + \text{O}_2 \rightarrow 2 \text{MgO}\]. b. \(\text{Fe}\), balanced: \[4 \text{Fe} + 3 \text{O}_2 \rightarrow 2 \text{Fe}_2\text{O}_3\]. c. \(\text{LiCl}\), balanced: \[2 \text{Li} + \text{Cl}_2 \rightarrow 2 \text{LiCl}\]. d. \(\text{I}_2\), balanced: \[ \text{Ca} + \text{I}_2 \rightarrow \text{CaI}_2 \].

Step-by-step solution

Identify the missing reactant or product for part (a)

For the reaction \(\text{Mg} + \text{_________} \rightarrow \text{MgO}\), determine what is needed to form magnesium oxide (MgO). Magnesium oxide is a compound consisting of magnesium and oxygen. Hence, the missing reactant is \(\text{O}_2\).

Balance the equation for part (a)

The unbalanced equation is: \(\text{Mg} + \text{O}_2 \rightarrow \text{MgO}\). To balance it, we need to ensure the same number of each type of atom on both sides of the equation. The balanced equation is: \[2 \text{Mg} + \text{O}_2 \rightarrow 2 \text{MgO}\].

Identify the missing reactant or product for part (b)

For the reaction \(\text{_________} + \text{O}_2 \rightarrow \text{Fe}_2\text{O}_3\), determine what reacts with oxygen to produce iron(III) oxide (Fe2O3). The missing reactant is iron (Fe).

Balance the equation for part (b)

The unbalanced equation is: \(\text{Fe} + \text{O}_2 \rightarrow \text{Fe}_2\text{O}_3\). To balance this, we place appropriate coefficients: \[4 \text{Fe} + 3 \text{O}_2 \rightarrow 2 \text{Fe}_2\text{O}_3\].

Identify the missing reactant or product for part (c)

For the reaction \(\text{Li} + \text{Cl}_2 \rightarrow \text{_________}\), determine the product formed from lithium and chlorine. The product is lithium chloride (LiCl).

Balance the equation for part (c)

The unbalanced equation is: \(\text{Li} + \text{Cl}_2 \rightarrow \text{LiCl}\). To balance this, we ensure there are 2 chlorine and 2 lithium atoms: \[2 \text{Li} + \text{Cl}_2 \rightarrow 2 \text{LiCl}\].

Identify the missing reactant or product for part (d)

For the reaction \(\text{Ca} + \text{_________} \rightarrow \text{CaI}_2\), determine what reacts with calcium to form calcium iodide (CaI2). The missing reactant is iodine (I2).

Balance the equation for part (d)

The unbalanced equation is: \(\text{Ca} + \text{I}_2 \rightarrow \text{CaI}_2\). This equation is already balanced as written: \[ \text{Ca} + \text{I}_2 \rightarrow \text{CaI}_2 \].

Key concepts

Balancing Chemical Equations

Balancing chemical equations is a fundamental skill in chemistry. Imagine a balance scale; both sides must be equal. Similarly, in a chemical equation, the number of atoms for each element should be the same on both the reactant and product sides.
This ensures the law of conservation of mass is maintained.
The steps are simple:

• Write the unbalanced equation.
• Count the number of atoms for each element on both sides.
• Add coefficients to balance the atoms.
• Check your work.

Using this approach allows for consistent and accurate balance in chemical reactions.
For example, an unbalanced equation like: \[\mathrm{Mg}+ \mathrm{O}_2 \longrightarrow \mathrm{MgO}\]
becomes balanced by adding appropriate coefficients: \[2 \mathrm{Mg}+ \mathrm{O}_2 \longrightarrow 2 \mathrm{MgO}\]

Synthesis Reactions

Synthesis reactions are a type of chemical reaction where two or more simple substances combine to form a more complex product. They follow the general formula: \[\text{A} + \text{B} \rightarrow \text{AB}\]
These reactions are common and occur in everyday life. For example, the rusting of iron or the formation of water from hydrogen and oxygen.
Synthesis reactions are crucial in various industries, including pharmaceuticals and materials science.
An example from our exercise: \[\mathrm{Li} + \mathrm{Cl}_2 \longrightarrow \mathrm{LiCl}\]
In this reaction, lithium metal reacts with chlorine gas to form lithium chloride.

Chemical Reactants and Products

In any chemical reaction, the substances you start with are called reactants, and the new substances formed are called products. Understanding the nature of both is key to mastering chemical equations.
Reactants are like the ingredients in a recipe, and products are the final dish. In a chemical context, the atoms in the reactants rearrange to form the products.
For instance, in our exercise part (d): \[\mathrm{Ca} + \mathrm{I}_2 \longrightarrow \mathrm{CaI}_2\]
Calcium (reactant) combines with iodine (reactant) to create calcium iodide (product).
The reactants provide the necessary atoms for the new molecular structure of the product.