Presentation on theme: " A plain baloney sandwich consists of two pieces of bread and one slice of baloney. You are given one package of baloney that contains eight (8) slices."— Presentation transcript:
A plain baloney sandwich consists of two pieces of bread and one slice of baloney. You are given one package of baloney that contains eight (8) slices of baloney, and one loaf of bread that contains thirty (30) pieces of bread.
Think of the sandwich making as a chemical reaction. The reactants will be the baloney and the bread, and the product will be the sandwich. Baloney + Bread Sandwich
Based on this information, what is the maximum amount of sandwiches that can be made? › Eight (8) Which reactant is limiting? › The baloney. Since it is a smaller amount, it gets completely used up and limits the amount of sandwiches that can be made Which reactant is in excess? › The bread. Since it is a larger amount, it doesn’t get completely used up, and there is plenty of bread left over.
Chemical reactions behave in the same fashion – there is often a reactant that gets completely used up in the reaction. It is this reactant that “limits” or determines the amount of products that can be produced. On the flip side, the other reactant is often found in large, excess amounts. This reactant is in excess – that is, there is more of it present than is needed in the reaction. Therefore, there will be some of it left over after the reaction takes place. In chemistry, it is crucial that we learn how to determine which reactant is limiting and which reactant is in excess.
Also known as “Limiting Reagent” Refers to the reactant that gets completely used up in a chemical reaction This reactant is the one that limits or determines the amount of products that can be produced in a reaction MUST BE DETERMINED IN MOLES! (NOT grams) The ONLY time you will need to determine the limiting reactant is when the question gives you information about two (2) REACTANTS
Determining the limiting reactant allows us to correctly solve stoichiometry calculations When we are given information about both reactants in a question, the limiting reactant is the information that we use to complete the calculation. YOU MUST USE THE INFORMATION OF THE LIMITING REACTANT! Otherwise your answer will be incorrect.
When we are faced with a limiting reactant stoichiometry question, we still follow the same basic four (4) steps › 1) Determine a balanced chemical equation › 2) Take your given information and go to moles Once you get your information to moles, determine the limiting reactant Take the number of moles for each reactant and divide them by their coefficients from the balanced chemical equation The SMALLER value is the limiting reactant › 3) Use the MOLAR RATIOS from the balanced chemical equation to identify the number of moles for the chemical you need › (using the information of the limiting reactant) › 4) Go where the question asks (using the information of the limiting reactant)