How are chemical reactions represented?

2 Answers
Feb 16, 2017

#"A stoichiometrically balanced equation must be written............"#


#"Garbage out must EQUAL Garbage in..........."#

This is the basis for any problem in stoichiometry. A relevant example is the combustion of hydrocarbons. Given the mass of an alkane, say #"heptane"#, we can predict precisely the mass of the carbon dioxide product given the mass of the starting #"heptane"# reactant, and all on the basis of our knowledge of stoichiometry:

#C_7H_16(l) + 11O_2(g) rarr 7CO_2(g) + 8H_2O(l)#

And if it ain't balanced (is it?) it's not in the race as a representation of physical (chemical) reality, because all chemical reactions are balanced with respect to mass and charge. Note that the equation as written is not only balanced with respect to mass and charge, it is also balanced with respect to energy. We could modify the equation to show how energy transfers in this reaction (how does it?). This also follows the principle of stoichiometry.

Feb 16, 2017

You always start with a balanced equation.


In a balanced equation, the coefficient in front of an element or compound is the number of moles of each element or compound.

The balanced equation for the decomposition of water by electrolysis is: #"2H"_2"O"stackrel("electricity")rarr##"2H"_2 + "O"_2"#

This tells us that two moles of water decompose to produce two moles of hydrogen gas and one mole of oxygen gas.