what does coefficients in equations mean, in chemical terms?
2NaCl means we have two molecules or 2 mols of NaCl. Most texts caution us not to use molecules but to stick with the latter part of the definition (moles); however, I don't have any problem with saying,
2H2 + 2 O2 ==> 2 H2O
2 molecules of H2 will react with 2 molecules of O2 to produce 2 molecules of H2O. 2 mols of H2 will react with 2 mols O2 to produce 2 mols H2O.
In chemical equations, coefficients represent the relative amounts of each substance involved in a reaction. They provide information about the stoichiometry of the reaction, which is the quantitative relationship between the reactants and products.
The coefficient in front of a substance represents the number of units of that substance involved in the reaction. In the equation you provided, "2H2 + 2 O2 ==> 2 H2O," the coefficient "2" indicates that two molecules or two moles of H2 are reacting with two molecules or two moles of O2 to produce two molecules or two moles of H2O.
Using coefficients helps balance the equation to ensure that the total number of atoms of each element is the same on both sides of the equation. It allows us to determine the exact proportions of reactants and products in a chemical reaction.