Problem 1 - Chemistry and Chemical Reactivity

Question

Write balanced chemical equations for the following reactions. (a) The reaction of aluminum and iron(III) oxide to form iron and aluminum oxide (known as the thermite reaction, page 142). (b) The reaction of carbon and water at high temperature to form a mixture of gaseous \(\mathrm{CO}\) and \(\mathrm{H}_{2}\) (known as water gas and once used as a fuel). (c) The reaction of liquid silicon tetrachloride and magnesium forming silicon and magnesium chloride. This is one step in the preparation of ultrapure silicon used in the semiconductor industry.

Step-by-Step Solution

Answer

(a) 2Al + Fe₂O₃ → 2Fe + Al₂O₃ (b) C + H₂O → CO + H₂ (c) SiCl₄ + 2Mg → Si + 2MgCl₂

Step 1: Identify reactants and products for reaction (a)

The reactants given for reaction (a) are aluminum (Al) and iron(III) oxide (Fe₂O₃). The products formed from this reaction are iron (Fe) and aluminum oxide (Al₂O₃).

Step 2: Write the unbalanced chemical equation for reaction (a)

Write the unbalanced chemical equation: Al + Fe₂O₃ → Fe + Al₂O₃

Step 3: Balance the chemical equation for reaction (a)

To balance this equation, ensure the number of atoms for each element is equal on both sides. Unbalanced: Al + Fe₂O₃ → Fe + Al₂O₃ First, balance Al: 2Al + Fe₂O₃ → Fe + Al₂O₃ Then, balance Fe: 2Al + Fe₂O₃ → 2Fe + Al₂O₃

Step 4: Identify reactants and products for reaction (b)

The reactants given for reaction (b) are carbon (C) and water (H₂O). The reaction produces a mixture of carbon monoxide (CO) and hydrogen gas (H₂).

Step 5: Write the unbalanced chemical equation for reaction (b)

Write the unbalanced chemical equation: C + H₂O → CO + H₂

Step 6: Balance the chemical equation for reaction (b)

Ensure the number of atoms for each element is equal on both sides. Unbalanced: C + H₂O → CO + H₂ This equation is already balanced as the number of each type of atom is equal on both sides.

Step 7: Identify reactants and products for reaction (c)

The reactants given for reaction (c) are silicon tetrachloride (SiCl₄) and magnesium (Mg). The products are silicon (Si) and magnesium chloride (MgCl₂).

Step 8: Write the unbalanced chemical equation for reaction (c)

Write the unbalanced chemical equation: SiCl₄ + Mg → Si + MgCl₂

Step 9: Balance the chemical equation for reaction (c)

To balance this equation: Unbalanced: SiCl₄ + Mg → Si + MgCl₂ First, balance Cl by ensuring there are enough MgCl₂ to account for all Cl in SiCl₄: SiCl₄ + 2Mg → Si + 2MgCl₂

Key Concepts

Thermite Reaction

The thermite reaction is a highly exothermic process where aluminum reacts with iron(III) oxide to form iron and aluminum oxide. This reaction is used in applications requiring extremely high temperatures, such as welding metals or cutting through steel.

Let's break down the balanced chemical equation for this reaction. The unbalanced equation is:

• Al + Fe₂O₃ → Fe + Al₂O₃

To balance it, we start with the aluminum atoms:

• Add a coefficient of 2 in front of Al to balance the aluminum atoms: 2Al.

Next, we balance the iron atoms:

• Add a coefficient of 2 in front of Fe to match the number of iron atoms from Fe₂O₃.

Thus, the balanced equation becomes:

• 2Al + Fe₂O₃ → 2Fe + Al₂O₃

This balanced equation shows that 2 moles of aluminum react with 1 mole of iron(III) oxide to produce 2 moles of iron and 1 mole of aluminum oxide.

Water Gas

The water gas reaction, known for producing a mixture of gases like carbon monoxide and hydrogen, involves carbon reaction with water at high temperatures. This mixture was historically used as a fuel because of its high energy content.

Here’s how we balance this reaction. The given unbalanced chemical equation is:

• C + H₂O → CO + H₂

Thankfully, this equation is already perfectly balanced. It reflects one molecule of carbon reacting with one molecule of water to yield one molecule of carbon monoxide alongside one molecule of hydrogen gas.

Since the same number of each atom type exists on both sides, the balanced equation keeps the reaction simple. This simplicity makes it useful in generating syngas (synthetic gas) for various industrial applications.

Silicon Tetrachloride Reaction

In the process of producing ultrapure silicon for semiconductors, silicon tetrachloride reacts with magnesium. This chemical reaction yields silicon and magnesium chloride as products.

The initial unbalanced equation is:

• SiCl₄ + Mg → Si + MgCl₂

To balance the chlorine atoms, note that there are 4 chlorine atoms in SiCl₄. Therefore, place a coefficient of 2 in front of MgCl₂, yielding 4 chlorine atoms:

• SiCl₄ + 2Mg → Si + 2MgCl₂

Now, the magnesium atoms are also balanced, with 2 atoms on each side. This gives us the balanced equation, ensuring both sides of the equation contain the same number of each type of atom. This reaction is key to preparing silicon for use in the electronics industry, which demands materials of the highest purity.