Re: What is process called when gases go back to solids?

Here are some definitions from technical dictionaries.  As you can see, it 
depends on the field of science you are in and really who you are talking to.. 

Deposition simply means to deposit.  When CO2 goes from vapor to dry ice it is 
deposited so deposition takes place.

Sublimation usually refers to a change in state from gas to liquid (meteorology 
usually) or solid or vice versa.

Condensation has many definitions outlined below.





Sublimation - The transmission of a substance directly from the solid state to 
the vapor state, or vice versa, without passing through the intermediate liquid 
state. 

Sublimation n 1: (chem) a change directly from the solid to the gaseous state 
without becoming liquid 2: (psych) modifying the natural expression of an 
impulse or instinct (esp a sexual one) to one that is socially acceptable.



Condensation - Specifically, in meteorology, the transformation from vapor to 
liquid. 

CONDENSATION—(1) (Physics) The process by which a gas or vapor changes to a 
liquid or solid; also the liquid or solid so formed. (2) (Chemistry) A chemical 
reaction in which water or another simple substance is released by the 
combination of two or more molecules. The opposite of Evaporation. In 
meteorological usage, this term is applied only to the transformation from vapor 
to liquid. 

Condensation \Con`den*sa"tion\, n. [L. condensatio: cf. F. condensation.] 1. The 
act or process of condensing or of being condensed; the state of being 
condensed. 

2. (Physics) The act or process of reducing, by depression of temperature or 
increase of pressure, etc., to another and denser form, as gas to the condition 
of a liquid or steam to water. 

3. (Chem.) A rearrangement or concentration of the different constituents of one 
or more substances into a distinct and definite compound of greater complexity 
and molecular weight, often resulting in an increase of density, as the 
condensation of oxygen into ozone, or of acetone into mesitylene. 

Condensation product (Chem.), a substance obtained by the polymerization of one 
substance, or by the union of two or more, with or without separation of some 
unimportant side products. 

condensation n 1: (psycholanalysis) an unconscious process whereby two ideas or 
images combine into a single symbol; especially in dreams 2: the process of 
changing from a gaseous to a liquid or solid state 3: atmospheric moisture that 
has condensed because of cold [syn: condensate] 4: the process or result of 
becoming smaller or pressed together: "the contraction of a gas on cooling" 
[syn: compression, contraction] 5: a shortened version of a written work [syn: 
abridgement, abridgment] 6: the act of increasing the density of something [syn: 
condensing]