Question

Explain the steps of the oxidation-number method of balancing equations.

Short answer

To balance equations using the oxidation-number method, follow these steps: 1. Assign oxidation numbers to each atom in the reactants and products. 2. Identify elements that change oxidation states during the reaction. 3. Calculate the changes in oxidation numbers for these elements. 4. Adjust coefficients to balance the electrons gained and lost in the redox process. 5. Balance the remaining atoms in the equation. 6. Check that the equation is properly balanced in terms of charges and atom quantities.

Step-by-step solution

Assign oxidation numbers

Each atom in a molecule is assigned an oxidation number, which represents the atom's charge if the molecule were separated into its individual components. There are several rules for assigning oxidation numbers, but here are the most common ones: 1. The oxidation state of an element in its elemental form is 0. 2. The oxidation state of oxygen in most compounds is -2 (except for peroxides, where it is -1). 3. The oxidation state of hydrogen in most compounds is +1 (except for metal hydrides, where it is -1). 4. The sum of the oxidation states of all atoms in a compound should equal the overall charge of the compound.

Identify the elements that change oxidation states

Identify the reactant and product species whose oxidation numbers have changed during the reaction. These are the elements that are either oxidized (lose electrons) or reduced (gain electrons).

Determine the change in oxidation numbers

For each element that changed its oxidation state, calculate the difference between the initial and final oxidation numbers. This will show how many electrons were gained or lost by each of the participating elements during the redox reaction.

Balance the electrons gained and lost

Adjust the coefficients of the species in the equation such that the total increase in oxidation numbers equals the total decrease in oxidation numbers. This ensures that the number of electrons lost in the oxidation process is equal to the number of electrons gained in the reduction process.

Balance the remaining atoms

Once the redox part of the equation is balanced, check to make sure that other atoms in the equation are also balanced. Adjust the coefficients of any species if necessary to achieve an overall balanced equation.

Check the balanced equation

Ensure that the equation is properly balanced by verifying that the sum of the charges on each side is equal and that the same number of atoms for each element is present on both sides of the equation. By following these steps, you should be able to balance equations using the oxidation-number method successfully.

Key concepts

Balancing Chemical Equations

Balancing chemical equations is a fundamental skill in chemistry which ensures that matter is neither created nor destroyed during a chemical reaction. To balance a chemical equation, one must ensure that the number of atoms for each element is the same on both the reactant and the product sides of the equation. This reflects the law of conservation of mass.
One way to achieve this is through the oxidation-number method, which involves tracking changes in the oxidation states of elements. This method can help identify the transfer of electrons, which is crucial in redox reactions. It's a systematic approach that ensures all elements are balanced, not just in terms of atom counts, but also in terms of electron transfer too.

By following a step-by-step approach, you can systematically adjust coefficients to achieve balance without having to guess the correct proportions, thereby increasing accuracy in representing the chemical process.

Oxidation States

Oxidation states, also known as oxidation numbers, are vital for identifying how electrons are transferred during chemical reactions. These states represent the hypothetical charges an atom would have if all bonds to atoms of different elements were completely ionic.
Assigning oxidation numbers helps in:

• Determining which atoms lose or gain electrons.
• Identifying the elements undergoing oxidation and reduction.
• Ensuring that the charges in a chemical equation are balanced.

A few general rules for assigning oxidation states include:

• Elements in their natural state have an oxidation state of zero.
• Oxygen generally has an oxidation state of -2 in compounds, while hydrogen is usually +1.
• The sum of oxidation states in a neutral compound must equal zero, and in ions, it should equal the ion's charge.

By using these guidelines, you can easily assign oxidation states and utilize them effectively for balancing equations.

Redox Reactions

Redox reactions, short for reduction-oxidation reactions, are a family of reactions that involve the transfer of electrons between chemical species. These reactions are characterized by a change in oxidation states between the reactants and products.
Reduction and oxidation always occur simultaneously, that's why they're often symbiotic in reactions:

• Oxidation refers to the loss of electrons and an increase in oxidation state.
• Reduction refers to the gain of electrons and a decrease in oxidation state.

An easy way to remember this is "LEO the lion says GER" - Lose Electrons: Oxidation, Gain Electrons: Reduction. By identifying which elements are oxidized and which are reduced, one can use the oxidation-number method to balance the electron transfer, confirming that the redox reaction is properly balanced.

Electron Transfer

Electron transfer is at the heart of redox reactions, where electrons are moved from one reactant to another. Understanding this concept is essential, as it explains how and why the chemical species' oxidation states change.
Every redox reaction involves:

• Electron donor: the species that provides electrons, undergoing oxidation.
• Electron acceptor: the species that receives electrons, undergoing reduction.

By tracking these electrons, you can precisely balance redox reactions using the oxidation-number method. This involves ensuring that the number of electrons lost by the oxidizing agent equals the number gained by the reducing agent.
Understanding electron transfer helps bring clarity to the energy changes and transformations involved in chemical reactions.

Chemical Reactions

Chemical reactions are processes that involve the rearrangement of atoms to form new substances. These reactions are foundational to understanding chemistry, as they explain how different substances interact and transform.
Chemical reactions include:

• Reactants: the starting substances that undergo chemical change.
• Products: the new substances formed as a result of a reaction.

There are various types of chemical reactions, including synthesis, decomposition, single displacement, double displacement, and redox reactions. Using the oxidation-number method particularly aids in balancing redox reactions where electron transfer occurs.
Each chemical reaction follows conservation laws, ensuring that both mass and charge are preserved, making balanced equations crucial for accurate chemical representation.