# Chemical reaction equation, historical question

I am reading a chemistry book printed in 1805. The chemical reaction equations are written using the equality symbol = instead of the arrow →, which is used in modern times.
Anyway sometimes it is still possible to see the "old fashioned" way:
http://www.jeron.je/anglia/learn/sec/science/changmat/page13.htm

Does anyone know why the equality symbol was abandoned, and when did it happen
in the history of chemistry? Are there reasons why this change was needed?
I know only a little about chemistry, I think this is a very basic question, but I cannot
seem to find the complete solution myself. I can think that maybe the = was replaced by → because chemical reaction equations are not mathematical equations, there is no equality
in the equation in mathematical sense.

If the chemical equations are not mathematics, then why the addition symbol + has not
been replaced by something else? The addition is a mathematical operation, so should
it be understood to mean also a chemical reaction? Something is added into something
else, perhaps this is an universal concept applicable not just in mathematics.

PhysicoRaj
Gold Member
An arrow indicates direction, whereas an equality sign does not.

DrDu
As long as a reaction is not in equilibrium, the reaction proceeds in one or the other direction. Hence it is more convenient to use arrows. In some situations, it is also necessary to distinguish formally between reactands and products, e.g. in calculating the potential of a electrochemical half cell, you divide by convention the product of the concentration of the products by that of the reactands.

Ok, there is a direction in chemical equation, reactants are cause and products are effect,
hence there is causality. But not in mathematical equation, there is symmetry in mathematical
equation instead of causality. 1+1→2 does not make sense because 2 is not caused by 1+1,
instead there is symmetry: 1+1=2 and 2=1+1.

Perhaps this is a weakness of mathematics, it does not seem offer causality.

256bits
Gold Member
I found this.

chemistry and symbols
http://www.chemistryviews.org/details/ezine/2746271/History_and_Usage_of_Arrows_in_Chemistry.html

1789 Lavoisier uses "=" sign for a chemical equation.
1884 Vant Hoff uses double arrows
1901 single arrow to designate direction, products and reactants
http://www.chemistryviews.org/SpringboardWebApp/userfiles/chem/image/2012/2012_November/Arrow [Broken]

http://www.chemistryviews.org/SpringboardWebApp/userfiles/chem/image/2012/2012_November/Arrow [Broken]

Other uses of arrows in chemistry shown, past and present.

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PhysicoRaj
Gold Member
Nice links. This timeline was very interesting→ 