Problem 91 - Chemistry: The Central Science

Question

Uranium hexafluoride, \(\mathrm{UF}_{6}\), is processed to produce fuel for nuclear reactors and nuclear weapons. \(\mathrm{UF}_{6}\) is made from the reaction of elemental uranium with \(\mathrm{ClF}_{3}\), which also produces \(\mathrm{Cl}_{2}\) as a by-product. (a) Write the balanced molecular equation for the conversion of \(\mathrm{U}\) and \(\mathrm{ClF}_{3}\) into \(\mathrm{UF}_{6}\) and \(\mathrm{Cl}_{2}\). (b) Is this a metathesis reaction? (c) Is this a redox reaction?

Step-by-Step Solution

Answer

(a) The balanced molecular equation is: \(\mathrm{U + 2ClF_3 \rightarrow UF_6 + 2Cl_2}\). (b) This is not a metathesis reaction, as no exchange of ions occurs between the reactants to form products. (c) This is a redox reaction, as the oxidation number of \(\mathrm{U}\) increases and the oxidation number of \(\mathrm{Cl}\) decreases, indicating a transfer of electrons.

Step 1: Write the unbalanced equation

We know the reactants and products of the reaction, so we write the unbalanced equation: \(\mathrm{U + ClF_3 \rightarrow UF_6 + Cl_2}\)

Step 2: Balance the equation

To balance the equation, we will ensure equal amounts of atoms for each element on both sides. Strike a balance for U: already balanced (1 on each side). Strike a balance for Cl: multiply ClF3 by 2 (2 on each side). Strike a balance for F: multiply ClF3 by 2 (6 on each side). Now the balanced molecular equation is: \(\mathrm{U + 2ClF_3 \rightarrow UF_6 + 2Cl_2}\) (b)

Step 3: Metathesis reaction identification

Given the balanced molecular equation: \(\mathrm{U + 2ClF_3 \rightarrow UF_6 + 2Cl_2}\) This reaction is not a metathesis reaction because no exchange of ions occurs between the reactants to form products. The \(\mathrm{Cl}\) and \(\mathrm{F}\) atoms are bonded together in both reactants and products. (c)

Step 4: Redox reaction identification

Assign oxidation numbers to each element in the balanced molecular equation: \(\mathrm{U}\): 0, \(\mathrm{Cl}\) in \(\mathrm{ClF_3}\): +3, \(\mathrm{F}\) in \(\mathrm{ClF_3}\): -1, \(\mathrm{U}\) in \(\mathrm{UF_6}\): +6, \(\mathrm{F}\) in \(\mathrm{UF_6}\): -1, \(\mathrm{Cl}\) in \(\mathrm{Cl_2}\): 0. The oxidation number of \(\mathrm{U}\) goes from 0 to +6, meaning it lost 6 electrons (oxidation). The oxidation number of \(\mathrm{Cl}\) goes from +3 to 0, meaning it gained 3 electrons (reduction). Since both oxidation and reduction occur simultaneously, this is a redox reaction.

Key Concepts

Redox Reactions

Redox reactions, short for reduction-oxidation reactions, involve the transfer of electrons between chemical species. In the given reaction between uranium ( U ) and chlorine trifluoride ( ClF_3 ), we see a prime example of a redox reaction in action.

Here, uranium starts with an oxidation state of 0 and changes to +6. This change means uranium loses 6 electrons, undergoing oxidation. On the flip side, chlorine, which starts in ClF_3 with an oxidation state of +3, shifts to 0 in the product Cl_2 . This indicates that chlorine gains 3 electrons, thus experiencing reduction.

Key points to remember about redox reactions:

• They always involve a complementary pair of reactions: oxidation and reduction.
• An increase in oxidation state corresponds to oxidation, while a decrease corresponds to reduction.
• The substance that gets oxidized is known as the reducing agent, and the one that gets reduced is called the oxidizing agent.

Balancing Chemical Equations

Balancing chemical equations is a foundational skill in chemistry that ensures that the same number of each type of atom is present on both sides of a chemical equation. This conservation respects the Law of Conservation of Mass, which states that mass cannot be created or destroyed in a chemical reaction.

In our exercise, we balanced the chemical equation for the reaction between uranium and chlorine trifluoride. Initially, the equation was unbalanced:\[ \mathrm{U + ClF_3 \rightarrow UF_6 + Cl_2} \]To balance this equation, you need to ensure that the number of each element is the same on both sides. We achieved balance by adjusting coefficients:
1. Uranium is already balanced with one atom on each side.
2. For chlorine, we placed a coefficient of 2 in front of ClF_3 and Cl_2.
3. Finally, fluorine also gets balanced because the adjustment in ClF_3 accounts correctly for six fluorine atoms.
The balanced equation becomes:\[ \mathrm{U + 2ClF_3 \rightarrow UF_6 + 2Cl_2} \]
Key things to remember when balancing equations:

• Start by balancing elements that appear in only one reactant and one product.
• Leave hydrogen and oxygen to be balanced last if they appear in more than one compound.
• Adjust coefficients as necessary, but never alter molecular formulas.

Nuclear Chemistry

Nuclear chemistry focuses on reactions that involve changes in an atom's nucleus. Although the mentioned exercise does not detail nuclear reactions, the context of uranium hexafluoride ( UF_6 ) hints at applications in nuclear chemistry due to uranium's significance as nuclear fuel.

Uranium is a heavy element with isotopes that are commonly used in nuclear reactors and for nuclear weapons. When U is used in nuclear applications, it undergoes a process called fission, where the nucleus splits into smaller parts, releasing a large amount of energy.

Points of interest in nuclear chemistry involving uranium:

• Uranium-235 and Uranium-238 are two significant isotopes, with ^{235}U being fissionable and quite crucial in nuclear reactors.


• Processing uranium into compounds like UF_6 is essential for isotope separation during enrichment.


• Nuclear chemistry involves understanding and handling radiation, which calls for stringent safety measures to protect humans and the environment.