1. Stoichiometry
Chapter 12

2. The Arithmetic of Equations
12.1
The Arithmetic of Equations
More 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.

3. Using Everyday Equations
12.1
Using Everyday Equations
A balanced equation is like a recipe.
It tells you quantitative information about a reaction.

4. The 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?

5. Interpreting Chemical Equations
In a balanced chemical equation, mass and atoms are conserved in every chemical reaction.

6. Using Balanced Chemical Equations
12.1
Using Balanced Chemical Equations
Chemists 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.

7. Writing and Using Mole Ratios
12.2
Writing and Using Mole Ratios
In 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.

8. Manufacturing plants produce ammonia by combining nitrogen with hydrogen. Ammonia is used in cleaning products, fertilizers, and in the manufacture of other chemicals.

9. Solving Stoichiometry Problems
When finding the amount of a substance needed or produced in a reaction, the mole ratio is always used.

10. Solving 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.

11. In this Hubble Space Telescope image, clouds of condensed ammonia are visible covering the surface of Saturn.

12. The electrolysis of water causes it to decompose into hydrogen and oxygen.

14. Limiting Reagent and Percent Yield
12.3
Limiting Reagent and Percent Yield
If 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.

15. Limiting and Excess Reagents
12.3
Limiting and Excess Reagents
Limiting and Excess Reagents
How is the amount of product in a reaction affected by an insufficient quantity of any of the reactants?

16. Limiting and Excess Reagents
12.3
Limiting and Excess Reagents
In 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.

17. Limiting and Excess Reagents
12.3
Limiting and Excess Reagents
The Chemical Equation for the Preparation of Ammonia
The “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?

20. Percent Yield 12.3 Percent Yield
What does the percent yield of a reaction measure?

21. 12.3
Percent Yield
The 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.

22. 12.3
Percent Yield
The 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.

23. 12.3
Percent Yield
The percent yield is the ratio of the actual yield to the theoretical yield expressed as a percent.