Question

The purification process of silicon involves the reaction of silicon tetrachloride vapor \(\left(\mathrm{SiCl}_{4}(g)\right)\) with hydrogen to \(1250^{\circ} \mathrm{C}\) to form solid silicon and hydrogen chloride. \((\mathbf{a})\) Write a balanced equation for this reaction. (b) What is being oxidized, and what is being reduced? (c) Which substance is the reductant, and which is the oxidant?

Short answer

The balanced chemical equation for the reaction is: \[\mathrm{SiCl}_{4}(g) + 2\mathrm{H}_{2}(g) \rightarrow \mathrm{Si}(s) + 4\mathrm{HCl}(g)\]. Silicon in \(\mathrm{SiCl}_{4}\) is reduced (oxidation state decreases from +4 to 0), while hydrogen in \(\mathrm{H}_{2}\) is oxidized (oxidation state increases from 0 to +1). Silicon tetrachloride \(\mathrm{SiCl}_{4}\) is the oxidant, and hydrogen gas \(\mathrm{H}_{2}\) is the reductant.

Step-by-step solution

Write the balanced chemical equation for the reaction

To write the balanced chemical equation, we begin by writing down the reactants and products, then balance the number of atoms for each element in the reaction. Reactants: \(\mathrm{SiCl}_{4}(g)\) and \(\mathrm{H}_{2}(g)\) Products: Solid silicon (Si) and hydrogen chloride (HCl) Now, let's balance the equation: \[\mathrm{SiCl}_{4}(g) + 2\mathrm{H}_{2}(g) \rightarrow \mathrm{Si}(s) + 4\mathrm{HCl}(g)\]

Identify the substances being oxidized and reduced

Oxidation and reduction refer to the change in oxidation states of elements in a reaction. If the oxidation state of an element increases, it is being oxidized, whereas if it decreases, it is being reduced. - In \(\mathrm{SiCl}_4\), the oxidation state of silicon (Si) is +4. - In \(\mathrm{H}_{2}\), the oxidation state of hydrogen (H) is 0. - In \(\mathrm{HCl}\), the oxidation state of hydrogen is +1. Comparing the oxidation states, we see that silicon's oxidation state has decreased from +4 to 0, implying it has been reduced. On the other hand, hydrogen's oxidation state has increased from 0 to +1, implying it has been oxidized.

Identify the reductant and oxidant

In a redox reaction, the substance that causes another substance to be reduced is called the oxidant, while the substance causing another substance to be oxidized is called the reductant. From Step 2, silicon is being reduced, which indicates that silicon tetrachloride (\(\mathrm{SiCl}_{4}(g)\)) is the oxidant. Hydrogen is being oxidized, which indicates that hydrogen gas (\(\mathrm{H}_{2}(g)\)) is the reductant.

Key concepts

Silicon purification

Silicon purification is a crucial process in the semiconductor industry.
To obtain high-quality silicon, methods like chemical vapor deposition are used. In this context, silicon tetrachloride (\(\mathrm{SiCl}_{4}\)) is reacted with hydrogen gas at high temperatures.
These reactions help in producing pure silicon by transforming silicon tetrachloride into solid silicon while releasing hydrogen chloride gas as a byproduct. This results in high-purity silicon, essential for electronics and solar panels.

• This process ensures silicon's properties meet strict industry standards.
• Temperature control is critical to maintain reaction efficiency.
• Such methods reduce impurities, improving silicon's quality and performance.

Oxidation state

The concept of oxidation state is key to understanding redox reactions.
Oxidation states show the electron loss or gain by elements in a compound.
This helps us understand which elements are oxidized or reduced during chemical reactions.

• In \(\mathrm{SiCl}_{4},\) silicon’s oxidation state is +4, indicating it donates this many electrons in reactions.
• Hydrogen in \(\mathrm{H}_{2}\) starts with an oxidation state of 0. In \(\mathrm{HCl},\) hydrogen's state changes to +1, showing electron uptake.
• A decrease in oxidation state means reduction, while an increase signifies oxidation.

By tracking these changes, we can dissect the roles of different substances in a reaction.

Chemical equations

Chemical equations provide a concise description of chemical reactions.
They use chemical formulas to show what happens when substances interact. It's important to balance these equations so each element has the same number of atoms on each side.
In the silicon purification reaction, we start with: \( \mathrm{SiCl}_{4}(g) + 2 ext{ }\mathrm{H}_{2}(g) ightarrow \mathrm{Si}(s) + 4 ext{ }\mathrm{HCl}(g) \).

• Balancing ensures mass conservation, a fundamental law of chemistry.
• Ensures predicted product quantities are accurate in any industrial application.
• Unbalanced equations may lead to inaccuracies in understanding of the reaction.

Accurate chemical equations are essential for understanding how substances transform in reactions.

Oxidants and reductants

Oxidants and reductants are central to redox reactions.
Oxidants accept electrons and get reduced. Reductants donate electrons and get oxidized.
Identifying them helps to understand the flow of electrons in a reaction.

• In the silicon purification process, silicon tetrachloride (\(\mathrm{SiCl}_{4}\)) acts as the oxidant, as it accepts electrons from hydrogen.
• Hydrogen gas (\(\mathrm{H}_{2}\)) serves as the reductant, losing electrons and being oxidized.
• This electron exchange is what drives chemical reactions, leading to the formation of products.

These roles are crucial for balancing redox equations and understanding chemical reaction mechanisms.