Reaction Types

Basic Reaction Types are based entirely on the formula:

Synthesis has multiple elements or molecules combining into a single compound. It is also sometimes known as a combination reaction.
- Example: H2 + O2 -> H2O
Decomposition has a single compound breaking apart.
- Example: H2O -> H2 + O2
Single replacement has an element replace a different element in a compound.
- Example: Li + AuOH -> LiOH + Au
Double displacement has two elements swap what they are bonded to.
- Example: AgNO3 + NaCl -> AgCl + NaNO3

Synthesis

Decomposition

Single Replacement

Double Displacement

Specific Reaction Types are based on the process that is occurring:

Acid-Base (also known as Neutralization): Acids and bases reacting. Acids generally start with H and Bases generally end with OH.
- Example: HCl (aq) + NaOH (aq) -> NaCl (aq) + H2O (l)
Combustion: Oxygen reacting with a fuel source (and fire) forming carbon dioxide and water vapor as products. The fuel source is organic in nature, meaning it's mostly carbon and hydrogen. Incomplete combustion also creates carbon monoxide and if there are particulates even more may be created on top of the standard CO2 and H2O.
- Example: CH4 (g) + O2 (g) -> CO2 (g) + H2O (g)
Precipitation: Solid forms. This can be determined based on the solubility rules below (soluble means it won't form a solid when mixed with that specific ion)
- Example: AgNO3 (aq) + NaCl (aq) -> AgCl (s) + NaNO3 (aq)
Oxidation-Reduction (also known as Redox): Electrons transfer. It's a redox reaction if it isn't one of the other 3.
- Example: Li (s) + Ca(OH)2 (aq) -> LiOH (aq) + Au (s)

Solubility Rules

Precipitation reactions have 2 primary pieces to them. The first thing you need to do is look at the state symbols of your reactants. Both of these need to be aqueous for a reaction to be precipitation. Next, you need to swap what your anions are attached to and check your solubility rules for these new compounds. If either of them are insoluble, a reaction has happened and that is the solid that forms from the reaction!

Chemical Reactions and Forensics (PSA)

Some of the different ways chemical reactions and properties are used in forensics are as follows:

Drug Chemistry – Determines the presence of controlled substances
Trace Chemistry - Identification and comparison of materials from fires, explosions, paints, and glass.
Microscopy - Identification and comparison of hairs, fibers, woods, soils, building materials, insulation and a broad group of materials referred to as "particulate unknowns."
Biology/DNA - Presence and comparison of body fluids and dried stains such as blood and saliva.
Toxicology – Determines the presence of drugs and poisons in tissue, blood, urine and other body fluids.
Latent Prints - Identification and comparison of hidden impressions from sources like fingers, palms, feet, shoes, ears, lips or the tread on vehicle tires.
Firearms & Toolmarks - Examination and comparison of fired bullets, discharged cartridges, guns, gunpowder patterns, and marks left by erased serial numbers in metal or by burglary tools like a pry bar or screwdriver.
Questioned Documents - Side by side comparisons of questioned handwriting and hand printing, ink, paper, writing instruments, printers, photocopiers, additions, eradications, obliterations, watermarks, and impressions.

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