2INTERPRETING 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
4WHAT IS A LIMITING REACTANT? The reactant that limits the amount of product formedThe reactant that in an experiment is all used up
5Percent 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
6HOW 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.
7Thermochemical 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
8If 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)