Summary: Nuclear Reactions

What are Redox Reactions?

A Redox reaction is a chemical change in which electrons move between reactants. This is seen by changes in the oxidation state of species. A redox reaction can be split into two half-reactions: an oxidation half and a reduction half. Each half must be balanced so all electrons are accounted for.

Types of Redox Reactions

• Decomposition Reaction - a compound breaks down into simpler substances.
• Combination Reaction - two or more substances combine to form a single compound.
• Displacement Reaction - an atom or ion in a compound is replaced by another; further classified as Metal displacement and Non-metal displacement.
• Disproportionation Reaction - a single species is both oxidized and reduced.

Oxidation and Reduction

• Oxidation - loss of electrons; can also mean addition of oxygen or removal of hydrogen.
• Reduction - gain of electrons; can also mean addition of hydrogen or removal of oxygen.
• Every redox change contains both oxidation and reduction occurring simultaneously.

Oxidizing and Reducing Agents

• Oxidizing agent - substance that gains electrons and is reduced.
• Reducing agent - substance that loses electrons and is oxidized.

Important Oxidizing Agents

• Molecules of highly electronegative elements (e.g., oxygen, halogens).
• Compounds with elements in high oxidation states (e.g., permanganates, chromates, strong oxyacids).
• Metal and non-metal oxides.
• Fluorine is noted as the strongest oxidizing agent.

Important Reducing Agents

• Most metals (e.g., sodium, zinc, iron, aluminium).
• Some non-metals (e.g., carbon, hydrogen, sulfur, phosphorus).
• Hydracids and certain low-oxidation-state compounds and metallic hydrides.
• Some organic compounds can act as reducing agents.

Reduction Potential

The standard electrode (reduction) potential of a half-reaction is the voltage relative to the standard hydrogen electrode. A positive reduction potential means the species is a stronger oxidizing agent than H+, while a negative value means it is weaker.

How to Identify Oxidizing and Reducing Agents

• If an element is in a high possible oxidation state in a compound, that compound can act as an oxidizing agent.
• If an element is in a low possible oxidation state in a compound, that compound can act as a reducing agent.
• If a highly electronegative element is in its highest oxidation state, the compound tends to be an oxidizing agent; in its lowest state it tends to be a reducing agent.
• To analyse a reaction: write the skeleton equation, assign oxidation numbers, identify species oxidized and reduced, add electrons to balance electron transfer, and scale half-reactions so electrons cancel.

Balancing Redox Reactions

• Two main methods: oxidation number (change in oxidation state) method and ion-electron (half-reaction) method.
• Oxidation number method uses equality of total electrons lost and gained to find coefficients.
• Ion-electron method (half-reaction) - common procedural steps follow:

• Separate the overall change into oxidation and reduction half-reactions.
• Balance all elements except O and H first.
• In acidic or neutral medium, balance O by adding H2O and H by adding H+.
• In alkaline medium, add H2O and OH- as needed to balance O and H.
• Balance charges by adding electrons.
• Multiply half-reactions by suitable integers so electrons cancel, then add the half-reactions and simplify.

Applications of Redox Reactions

• Electrochemistry - batteries and electrochemical cells produce electrical energy from redox reactions.
• Combustion - a form of oxidation-reduction; rapid combustion (explosion) is a fast redox process used in propellants.
• Photosynthesis - a redox process where CO2 is reduced to carbohydrates and water is oxidized to oxygen; sunlight supplies energy.
• Industrial and everyday uses: production of chemicals by electrolysis, water sanitizing and bleaching, corrosion protection using sacrificial anodes (galvanization), manufacture of cleaning products, production of acids via oxidation, electroplating, and metal extraction from ores.
• Oxygen-driven oxidation is a major cause of food spoilage.

What Happens in an Acid-Base Reaction?

An acid-base reaction is the reaction between an acid and a base that results in mutual neutralization. In these reactions the acid donates a proton and the base accepts a proton, forming a conjugate base and a conjugate acid. Such reactions are normally carried out at room temperature, in the absence of light, and heat is avoided when possible.