What does it mean for a substance to be incompatible?

Youse gots a bunch of idiots answering this here. TYpically the phrase ...incompatible with ... is used in the context of a MSDS (Material Safety Data Sheet) (aka SDS) or in safety information. Also with shipping of dangerous goods. Incompatible with means that should the one material come in contact with the other then some sort of safety concern arises. Could be explosion, toxic gas, heat, etc. It means that actually the materials ARE compatible in the sense they will mix or react but their contact is "incompatible with safety". Most times the materials in question need special conditions to be REALLY dangerous. It is used by fire departments and other first responders to evaluate the risks when an accident happens, and also to deterrmine where to store various materials. For instance acids and bases shouldn't be stored side-by-side since the chance of them mixing becomes much higher and they could give off heat and toxic fumes (mist). So incompatible with is best translated as "reacts with" or "avoid all contact between"

When certain hazardous chemicals are stored or mixed together, violent reactions may occur because the chemicals are unsuitable for mixing, or are incompatible. Classes of incompatible chemicals should be segregated from each other during storage, according to hazard class.

A wide variety of chemicals react dangerously when mixed with certain other materials. Some of the more widely-used incompatible chemicals are given below, but the absence of a chemical from this list should not be taken to indicate that it is safe to mix it with any other chemical!

For incompatible chemicals visit :

http://www.physchem.ox.ac.uk/MSDS/incompatibles.ht...

Oxidizing AgentsThe most common reagents are: H2CrO4; K2Cr2O7 + H2SO4; CrO3 + H2SO4; Hydrogen peroxide, H2O2, is a moderately strong oxidizing agent;

It means that magnesium will react with those chemicals which will result in fire, explosion or the release of gas. That is why acids are store with other acid, oxidizers with other oxidizers etc.....

Oxidizing agents r subs which oxidise othr subs nd themselves get reduced...which have the ability to gain electrons....non metals r good oxid agents

Incompatible means that it's not capable of being combined/used with anything else

if the substance is incompatible it means that it doesntmix with each other

it means that the substance does not react with certain acids.

IT MEANS DON'T MIX IT!