Synthesis Reactions: Step-by-Step Examples and Solutions

Understanding Synthesis Reactions ⚗️

A synthesis reaction, also known as a direct combination reaction, involves the combination of two or more reactants to form a single product. The general form is:

$$A + B \rightarrow AB$$

Let's explore some step-by-step examples.

Example 1: Formation of Water 💧

Hydrogen gas ($H_2$) reacts with oxygen gas ($O_2$) to form water ($H_2O$).

1. Write the unbalanced equation:

   $$H_2 + O_2 \rightarrow H_2O$$

2. Balance the equation:

   We need two oxygen atoms on both sides. Place a coefficient of 2 in front of $H_2O$.

   $$H_2 + O_2 \rightarrow 2H_2O$$

3. Balance hydrogen:

   Now we have four hydrogen atoms on the product side, so we need four on the reactant side. Place a coefficient of 2 in front of $H_2$.

   $$2H_2 + O_2 \rightarrow 2H_2O$$
4. Final balanced equation:

   $$2H_2 + O_2 \rightarrow 2H_2O$$

Example 2: Formation of Sodium Chloride (Table Salt) 🧂

Sodium ($Na$) reacts with chlorine gas ($Cl_2$) to form sodium chloride ($NaCl$).

1. Write the unbalanced equation:

   $$Na + Cl_2 \rightarrow NaCl$$

2. Balance the equation:

   We need two chlorine atoms on both sides. Place a coefficient of 2 in front of $NaCl$.

   $$Na + Cl_2 \rightarrow 2NaCl$$

3. Balance sodium:

   Now we have two sodium atoms on the product side, so we need two on the reactant side. Place a coefficient of 2 in front of $Na$.

   $$2Na + Cl_2 \rightarrow 2NaCl$$

4. Final balanced equation:

   $$2Na + Cl_2 \rightarrow 2NaCl$$

Example 3: Formation of Ammonia 🧪

Nitrogen gas ($N_2$) reacts with hydrogen gas ($H_2$) to form ammonia ($NH_3$).

1. Write the unbalanced equation:

   $$N_2 + H_2 \rightarrow NH_3$$

2. Balance the equation:

   We need two nitrogen atoms on both sides. Place a coefficient of 2 in front of $NH_3$.

   $$N_2 + H_2 \rightarrow 2NH_3$$

3. Balance hydrogen:

   Now we have six hydrogen atoms on the product side, so we need six on the reactant side. Place a coefficient of 3 in front of $H_2$.

   $$N_2 + 3H_2 \rightarrow 2NH_3$$

4. Final balanced equation:

   $$N_2 + 3H_2 \rightarrow 2NH_3$$

Example 4: Formation of Iron(III) Oxide (Rust) ⚙️

Iron ($Fe$) reacts with oxygen gas ($O_2$) to form iron(III) oxide ($Fe_2O_3$).

1. Write the unbalanced equation:

   $$Fe + O_2 \rightarrow Fe_2O_3$$

2. Balance the equation:

   We need two iron atoms on the product side, so we need two on the reactant side. Place a coefficient of 2 in front of $Fe_2O_3$.

   $$2Fe + O_2 \rightarrow Fe_2O_3$$

3. Balance oxygen:

   Now we have three oxygen atoms on the product side, and two on the reactant side. To balance, find the least common multiple (LCM) of 2 and 3, which is 6. Place a coefficient of 3 in front of $O_2$ and a coefficient of 2 in front of $Fe_2O_3$.

   $$2Fe + 3O_2 \rightarrow 2Fe_2O_3$$

4. Balance iron:

   Now we have four iron atoms on the product side, so we need four on the reactant side. Place a coefficient of 4 in front of $Fe$.

   $$4Fe + 3O_2 \rightarrow 2Fe_2O_3$$

5. Final balanced equation:

   $$4Fe + 3O_2 \rightarrow 2Fe_2O_3$$

Key Steps for Balancing Synthesis Reactions 📝

• Identify the reactants and products.
• Write the unbalanced equation.
• Balance elements one at a time by adjusting coefficients.
• Double-check that all elements are balanced.

Practice Problems ✍️

Try balancing these synthesis reactions:

• $Mg + O_2 \rightarrow MgO$
• $S + O_2 \rightarrow SO_3$