2The Arithmetic of Equations 12.1The Arithmetic of EquationsMore than 3000 cocoons are needed to produce enough silk to make just one elegant Japanese kimono. Like silk manufacturers, chemists must know how much reactant they need to make a certain amount of product. Determining the quantities of reactants and products in a reaction requires a balanced chemical equation.
3Using Everyday Equations 12.1Using Everyday EquationsA balanced equation is like a recipe.It tells you quantitative information about a reaction.
4The balanced chemical equation for the formation of ammonia can be interpreted in several ways. Predicting How many molecules of NH3 could be made from 5 molecules of N2 and 15 molecules of H2?
5Interpreting Chemical Equations In a balanced chemical equation, mass and atoms are conserved in every chemical reaction.
6Using Balanced Chemical Equations 12.1Using Balanced Chemical EquationsChemists use balanced chemical equations as a recipe to calculate how much reactant is needed or product is formed in a reaction.The calculation of quantities in chemical reactions is a subject of chemistry called stoichiometry.
7Writing and Using Mole Ratios 12.2Writing and Using Mole RatiosIn chemical calculations, mole ratios are used to convert between moles of one substance and moles of another substance.Mole ratios are obtained from a balanced chemical equation.Coefficients mean moles.
8Manufacturing plants produce ammonia by combining nitrogen with hydrogen. Ammonia is used in cleaning products, fertilizers, and in the manufacture of other chemicals.
9Solving Stoichiometry Problems When finding the amount of a substance needed or produced in a reaction, the mole ratio is always used.
10Solving Stoichiometry Problems Write a balanced equation to represent the reaction.Convert given quantities to moles.Use mole ratio to find moles of unknown.Convert found moles to unit needed.
11In this Hubble Space Telescope image, clouds of condensed ammonia are visible covering the surface of Saturn.
12The electrolysis of water causes it to decompose into hydrogen and oxygen.
14Limiting Reagent and Percent Yield 12.3Limiting Reagent and Percent YieldIf a carpenter had two tabletops and seven table legs, he could only build one four- legged table. The number of table legs is the limiting factor in the construction of four- legged tables. Similarly, in chemistry, the amount of product made in a chemical reaction may be limited by the amount of one or more of the reactants.
15Limiting and Excess Reagents 12.3Limiting and Excess ReagentsLimiting and Excess ReagentsHow is the amount of product in a reaction affected by an insufficient quantity of any of the reactants?
16Limiting and Excess Reagents 12.3Limiting and Excess ReagentsIn a chemical reaction, an insufficient quantity of any of the reactants will limit the amount of product that forms.The limiting reagent is the reagent that determines the amount of product that can be formed by a reaction.The reagent that is not used up is called the excess reagent.
17Limiting and Excess Reagents 12.3Limiting and Excess ReagentsThe Chemical Equation for the Preparation of AmmoniaThe “recipe” calls for 3 molecules of H2 for every 1 molecule of N2 . In this particular experiment, H2 is the limiting reagent and N2 is in excess. Inferring How would the amount of products formed change if you started with four molecules of N2 and three molecules of H2?
20Percent Yield 12.3 Percent Yield What does the percent yield of a reaction measure?
2112.3Percent YieldThe percent yield is a measure of the efficiency of a reaction carried out in the laboratory.A batting average is actually a percent yield.A batting average is actually a percent yield.
2212.3Percent YieldThe theoretical yield is the maximum amount of product that could be formed from given amounts of reactants.In contrast, the amount of product that actually forms when the reaction is carried out in the laboratory is called the actual yield.
2312.3Percent YieldThe percent yield is the ratio of the actual yield to the theoretical yield expressed as a percent.