2 INTERPRETING BALANCED CHEMICAL EQUATIONS STOICHIOMETRY IS THE STUDY OF THE QUANTITATIVE, OR MEASURABLE, RELATIONSHIPS THAT EXIST IN CHEMICAL FORMULAS AND CHEMICAL REACTIONS.N2H4 + 2 H2O2 -> N2 + 4 H2OThe coefficients can indicate the following:1 molecule N2H4 + 2 molecules H2O2 -> 1 molecule N2 + 4 molecules H2O1 mole N2H4 + 2 moles H2O2 -> 1 mole N2 + 4 moles H2O32 g N2H4 + 2(34 g) H2O2 -> 28 g N2 + 4 (18 g) H2O
4 WHAT IS A LIMITING REACTANT? The reactant that limits the amount of product formedThe reactant that in an experiment is all used up
5 Percent YieldMeasures the efficiency of a reaction carried out in the labTheoretical yield – the maximum amount of product that can form during a reaction (calculated)Actual yield – how much actually formsFactors causing % yield to be less than 100Reaction not completingImpure reactantsLoss of product during filtrationCareless measurement
6 HOW DO WE DETERMINE PERCENT YIELD? Although you can determine the amount of product that will be produced in a chemical reaction, in reality, that calculated amount is not always the actual amount obtained from the reaction.
7 Thermochemical Equation Shows the amount of heat produced or absorbed by a reactionEvery reactant will have a certain heat content, or enthalpy (H)The change in enthalpy (H) will tell us if the reaction is exo or endothermic
8 If H is positive, reaction is endothermic (heat is a reactant) Change in EnthalpyIf H is positive, reaction is endothermic (heat is a reactant)If H is negative, reaction is exothermic (heat is a product)