Question

When balancing redox equations, the number of electrons lost in the oxidation half-reaction must the number of electrons gained in the reduction half- reaction.

Short answer

To balance a redox equation, divide it into oxidation and reduction half-reactions, balance atoms and charges, then ensure the number of electrons exchanged is equal in both half-reactions before combining them.

Step-by-step solution

Split the Reaction into Two Half-Reactions

Divide the unbalanced redox reaction into two separate half-reactions – one for oxidation and one for reduction. Each half-reaction will show either the loss or gain of electrons, respectively.

Balance Atoms Other Than Oxygen and Hydrogen

Balance all the atoms in each half-reaction other than oxygen and hydrogen by adding appropriate coefficients.

Balance Oxygen Atoms

Balance the oxygen atoms by adding water (H2O) molecules to the side that requires oxygen.

Balance Hydrogen Atoms

Balance the hydrogen atoms by adding hydrogen ions (H+) to the side that requires hydrogen.

Balance the Charges

Balance the charges in each half-reaction by adding electrons (e-) to the more positive side or the less negative side, so that the charges on both sides of the half-reaction are equal.

Make Electron Transfer Equal

Ensure that the number of electrons lost in the oxidation half-reaction is equal to the number of electrons gained in the reduction half-reaction by multiplying the half-reactions by appropriate coefficients.

Combine the Half-Reactions

Combine the two half-reactions to form the balanced redox equation, ensuring that the number of electrons cancels out and all elements and charges are balanced.

Key concepts

Oxidation and Reduction Half-Reactions

Understanding oxidation and reduction half-reactions is crucial in mastering the art of balancing redox equations. In a redox reaction, one element loses electrons while another gains them. This process is split into two parts: oxidation, where electrons are lost, and reduction, where electrons are gained.

Each half-reaction represents one of these processes. For instance, if we have a metal that loses electrons, this is articulated as an oxidation half-reaction. Conversely, if an atom or ion gains electrons, we express this change as a reduction half-reaction. It's important to remember the mnemonic 'OIL RIG' which stands for 'Oxidation Is Loss, Reduction Is Gain', referring to the movement of electrons.

To balance these reactions, you start by identifying what is oxidized and what is reduced. Then you write out the half-reactions, ensuring to only focus on one process at a time. This segregation helps simplify the complex task of equation balancing.

Chemical Reaction Balancing

Chemical reaction balancing, especially in redox reactions, involves several precise steps to ensure that the same number of atoms for each element is present on both sides of the equation.

Initially, you'll balance atoms other than oxygen and hydrogen because these elements are often involved in the transfer of electrons and can be balanced later with water and hydrogen ions, respectively. After balancing the initial elements, you proceed to balance the oxygen atoms by adding water molecules to the side that lacks oxygen. Following this, hydrogen atoms are balanced by incorporating hydrogen ions into the equation.

The crucial step of balancing the charges is done by adding electrons to equalize the charge on both sides of a half-reaction. This process requires careful attention to detail and often involves adding electrons to the more positive side in oxidation and to the more negative side in reduction. Only when each half-reaction is balanced in terms of both mass and charge can you then move on to ensuring electron transfer equality.

Electrons Transfer in Redox Reactions

In redox reactions, the transfer of electrons from one species to another is what fundamentally constitutes the reaction. Electrons are transferred during oxidation and reduction processes, leading to a change in the oxidation states of the elements involved.

It's imperative to ensure that the number of electrons lost in the oxidation half-reaction is the same as the number gained in the reduction half-reaction. If these numbers do not initially match up, coefficients are used to multiply the half-reactions until they do. This step is vital for maintaining the conservation of charge and matter.

Finally, combining the adjusted half-reactions, while making sure that the electrons cancel out, gives us the balanced redox equation. This is the culmination of careful balancing where atoms, charges, and electrons must be accounted for to accurately reflect the physical chemistry of the reaction.