The+Meaning+of+Stoichiometry+and+the+Coefficients+in+a+Reaction+Equation

Ⅶ.1.The Meaning of Stoichiometry and the Coefficients in a Reaction Equation __ TEXT BOOK Page123-124 __


 * Purpose **

To understand the meaning of stoichiometry and be able to calculate the amount of a specific product created when a given amount of reactant is used and reverse.

The most important part of this lesson is calculation question.


 * Definition ** :


 * Stoichiometry: ** The relationship between the amount of reactants used in a chemical reaction and the amounts of products products produced by the reaction.(__Text P.123__)


 * Coefficients : ** The number which have the reactants and products behind in a chemical reaction equation. It represents the amount of reactants used and the amount of products produced in the reaction.

*Coefficients are not only used to balance reactions, but are useful in determining the reagent mixture ratios and can be used to predict the amount of each product produced.(__From Unit7 NOTES Page 1__ )
 * Question type **

In Ⅶ .1. the questions are simple. The questions will give the reaction equations and the amount of molecules/moles of one reactant or one product, the amount of molecules/moles of other reactants or products would be the answer.

Multiply the molecules/mols of given amount compound by the ratio of molecules/mols of the required amount compoud to given amount compound, we will get the answer.
 * How to calculate **


 * Important Notes **

1.Use completely-labelled units and the names of compounds (eg.“molecule N2” not just “molecule”). It helps determine the denominator and numerator of factors. 2.Do not forget Significant Figures.

Example **


 * 1)In the reaction equation N2+3H2——>2NH3. **

__ a)How many molecules of N2 are required to react with 30 molecules of H2? __


 * 1) of N2 molecules = 30 molecules H2×1 molecules N2 / 3 molecules H2 = 10molecules

__ b)How many moles of NH3 are produced when 9 mol of H2 are reacted? __


 * 1) of moles of N2 = 9 mol H2×2 mol NH3 / 3 mol H2 = 6mol


 * 2)In the reaction equation C3H8+5O2——>3CO2+4H2O.**

__ a)How many oxygen molecules react with 10 molecules of C3H8? __


 * 1) of O2 molecules = 10 molecules C3H8×5 molecules O2 / 1 molecules C3H8 = 50molecules

__ b)How many H2O molecules are produced when 3 molecules of C3H8 react? __


 * 1) of H2O molecules = 3 molecules C3H8×4 molecules H2O / 1 molecules C3H8 =12molecules

__ c)How many moles of oxygen molecules are needed to produced 12 mol of CO2? __


 * 1) of moles of O2 = 12 mol CO2×5 mol O2 / 3 mol CO2 = 20 mol

__ d)How many moles of CO2 are produced when 2 mol C3H8 are used up? __


 * 1) of moles of CO2 = 2 mol C3H8×3 mol CO2 / 1 mol C3H8 = 6 mol

TEXT BOOK-Page124 Exercise #1—5 NOTES Unit7
 * Practice Question **

For the suggestion that ask for answer of the questions in the test book, please turn to Page291 in the test, all the answers are there.