Question

Write a balanced equation for each of the following combination reactions: (a) Iron is heated with fluorine gas to yield iron(III) fluoride. (b) Lead is heated with phosphorus powder to yield lead(IV) phosphide.

Short answer

(a) 2Fe + 3F\(_2\) → 2FeF\(_3\); (b) 3Pb + 4P → Pb\(_3\)P\(_4\).

Step-by-step solution

Understanding the Reaction

In part (a), we are combining iron (Fe) with fluorine gas (F\(_2\)) to produce iron(III) fluoride (FeF\(_3\)). For part (b), lead (Pb) is combining with phosphorus (P) to form lead(IV) phosphide (Pb\(_3\)P\(_4\)). Identify the compounds involved and their usual oxidation states.

Determine Oxidation States

In iron(III) fluoride, the iron ion is in the +3 oxidation state, while each fluorine is in the -1 state. For lead(IV) phosphide, each lead ion is in the +4 state, and phosphorus is typically in the -3 state.

Writing Initial Equations

For reaction (a), start with the unbalanced equation: Fe + F\(_2\) → FeF\(_3\). For reaction (b), write the initial unbalanced equation as Pb + P → Pb\(_3\)P\(_4\).

Balancing Reaction for Iron and Fluorine

In the reaction Fe + F\(_2\) → FeF\(_3\), balance the iron atoms by placing a coefficient of 2 in front of Fe and 3 in front of F\(_2\): 2Fe + 3F\(_2\) → 2FeF\(_3\). This balances both the iron and fluorine atoms.

Balancing Reaction for Lead and Phosphorus

For Pb + P → Pb\(_3\)P\(_4\), start by balancing the phosphorus. Placing a coefficient of 4 in front of P yields: 3Pb + 4P → Pb\(_3\)P\(_4\). This balances both the lead and phosphorus atoms.

Key concepts

Oxidation States

Oxidation states, also known as oxidation numbers, indicate an element's degree of oxidation in a chemical compound. It's like assigning an imaginary charge to atoms within a molecule. Knowing the oxidation state helps us understand how electrons are distributed during a chemical reaction. For instance, in the reaction where iron is combined with fluorine gas to form iron(III) fluoride, the iron (Fe) exhibits an oxidation state of +3. Meanwhile, each fluorine (F) has an oxidation state of -1. This means iron gives away electrons, making it more positive, while fluorine gains electrons, making it more negative. Similarly, in lead(IV) phosphide, lead (Pb) has an oxidation state of +4, and phosphorus (P) typically adopts a -3 state. Recognizing these states is essential for balancing chemical equations, as it reflects the number of electrons exchanged.

Combination Reactions

Combination reactions occur when two or more substances combine to form a single product. This type of reaction is also known as a synthesis reaction. It generally features the joining of elements or simple compounds. An example from the original exercise shows iron reacting with fluorine gas to yield iron(III) fluoride. This demonstrates that multiple reactants have formed a single compound. - Combines elements or simpler compounds - Yields one product Another case from the exercise involves lead and phosphorus forming lead(IV) phosphide. This is also a combination reaction, as lead and phosphorus produce a single, more complex substance. Combination reactions often involve elements in their elemental forms reacting with each other.

Stoichiometry

Stoichiometry is the calculation of quantities in chemical reactions. It's all about measuring the amounts of different elements and compounds involved in chemical equations. When balancing equations, stoichiometry helps us ensure that the amount of each element is conserved. For instance, to balance the equation for the reaction between iron and fluorine, we determine that 2 iron atoms react with 3 molecules of fluorine gas to create 2 units of iron(III) fluoride: 2Fe + 3F\(_2\) → 2FeF\(_3\) This balanced equation demonstrates the principle that matter cannot be created or destroyed, only changed. In the case of lead and phosphorus, stoichiometry shows us that 3 atoms of lead react with 4 atoms of phosphorus to form lead(IV) phosphide:3Pb + 4P → Pb\(_3\)P\(_4\)Stoichiometry is crucial for predicting product amounts and ensuring balanced chemical equations.