20 Chemistry
Chapter 12
Stoichiometry & Chemical Reactions
Demo mixing hydrochloric acid with a sodium hydroxide. The products are salt and water. Does this mean that the container is completely safe? Why?
The idea is that the equation doesn’t show the entire picture. Depending on which reactant is the limiting reactant, there will be some harmful reactant leftover in addition to the two new products. We say that only one of the two reactants is completely “consumed” in the reaction. In order to completely consume both reactants so that neither is present after the reaction, stoichiometry is required.
Consider the burning of methane (CH4) for example.
The coefficients in front of each substance may represent the number of Molecules(formula units) or the number of moles. In order to determine exactly how much of each reactant is required so that each is completely consumed, convert the number of moles to mass.
number of molecules1 2 1 2
number of moles1 2 1 2
mass16g 64g 44g 36g
** Notice that the mass of the reactants is equal to the mass of the products – sound familiar?**
Also see sample p. 355
Try practice p. 356 # 1 a - e
Mole Ratios
For examples, consider the following
etc.
this will come in handy later
Practice p. 357 # 2, 3
Mol to Mol Conversions in Chemical Equations
See sample p. 359
Try p. 359 # 9, 10
Mass to Mass Conversions in Chemical Equations
See sample p. 360 – 361
Try p. 360 # 11, 12
try p. 362 # 13,14
Limited Reactants ( & therefore excess)
Consider mixing 56g of BaCl2 and 65g of Na2SO4.
1.What are the products?
2.How much product will there be?
3.How much excess will there be?
mass56g65gv) 62.7gv) 31.5 gviii) 26.8 g
M.M.i) 208g/moli) 142g/moli) 233g/moli) 58.5g/molvii) 142 g/mol
molsii) 0.269 molsii) 0.458 molsiv) 0.269 molsiv) 0.538molvi) 0.189 mols
iii) L.R.iii) E.R.
Sample p. 367
Try p. 368 # 20& 21