Stoichiometry

STOICHIOMETRY the study of the quantitative relationships that exist in chemical formulas and reactions

The key to understanding… The coefficients in a balanced equation give the relative amounts (in moles) of reactants and products.

The coefficients represent moles… 2NaCl  2Na + Cl2 There are ____ moles of salt. There are ____ moles of sodium. 2 There is ____ mole of diatomic Cl. 1

Sample Problem If you start with 50g of salt, how many grams of chlorine are produced when the salt is decomposed?

STEPS TO STOICHIOMETRY PROBLEMS

Write the balanced equation! STEP 1 Write the balanced equation!

Find the number of moles of the given substance STEP 2 Find the number of moles of the given substance

STEP 3 Use the balanced equation to find the ratio of moles of given substance to moles of needed substance

STEP 4 Convert moles of needed substance to whatever quantity is desired

Do you think that in the chemistry lab that we always get the amount of product that we calculate? No way!!

% Yield actual amount of a product expressed as a % of the theoretical amount of that substance

Calculated amount from stoichiometry Percent Yield Actual amount of product from the lab % Yield = Calculated amount from stoichiometry