Indicate whether the following balanced equations involve oxidation–reduction. If they do, identify the elements that undergo changes in oxidation number. (a) PBr₃(l) + 3 H₂O(l) → H₃PO₃(aq) + 3 HBr(aq)

Verified step by step guidance

1. Identify the oxidation states of each element in the reactants and products. For PBr₃, phosphorus (P) is typically in the +3 oxidation state, and bromine (Br) is in the -1 oxidation state. In H₂O, hydrogen (H) is +1, and oxygen (O) is -2.
2. Determine the oxidation states of each element in the products. In H₃PO₃, phosphorus (P) is typically in the +3 oxidation state, hydrogen (H) is +1, and oxygen (O) is -2. In HBr, hydrogen (H) is +1, and bromine (Br) is -1.
3. Compare the oxidation states of each element in the reactants and products to see if there is a change. If any element's oxidation state changes, the reaction involves oxidation-reduction.
4. Check if the oxidation state of phosphorus (P) changes from reactants to products. In this case, it remains +3, indicating no change.
5. Check if the oxidation state of bromine (Br) changes from reactants to products. In this case, it remains -1, indicating no change. Since there are no changes in oxidation states, this reaction does not involve oxidation-reduction.

Key Concepts

Oxidation-Reduction Reactions

Oxidation-reduction (redox) reactions involve the transfer of electrons between substances, leading to changes in oxidation states. In these reactions, oxidation refers to the loss of electrons (increase in oxidation number), while reduction refers to the gain of electrons (decrease in oxidation number). Identifying whether a reaction is a redox process requires analyzing the oxidation states of the elements involved before and after the reaction.

Oxidation States

Oxidation states (or oxidation numbers) are assigned to atoms in a compound to indicate their degree of oxidation or reduction. The rules for determining oxidation states include that the oxidation state of an element in its elemental form is zero, and for monoatomic ions, it equals the charge of the ion. Understanding how to assign oxidation states is crucial for identifying which elements are oxidized or reduced in a chemical reaction.

Balancing Chemical Equations

Balancing chemical equations ensures that the number of atoms for each element is the same on both sides of the equation, reflecting the law of conservation of mass. In redox reactions, balancing often involves ensuring that the total increase in oxidation states (loss of electrons) equals the total decrease in oxidation states (gain of electrons). This process is essential for accurately representing the stoichiometry of the reaction and understanding the electron transfer involved.