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So far, we have talked about chemical reactions in terms of individual atoms and molecules. Although this works, most of the reactions occurring around us involve much larger amounts of chemicals. Even a tiny sample of a substance will contain millions, billions, or a hundred billion billions of atoms and molecules. How do we compare amounts of substances to each other in chemical terms when it is so difficult to count to a hundred billion billion? Actually, there are ways to do this, which we will explore in this chapter. In doing so, we will increase our understanding of stoichiometry, which is the study of the numerical relationships between the reactants and the products in a balanced chemical reaction.
- 8.1: Climate Science And Carbon Dioxide
- Carbon dioxide (CO₂) is the primary greenhouse gas emitted through human activities. In 2015, CO₂ accounted for about 82.2% of all U.S. greenhouse gas emissions from human activities. Carbon dioxide is naturally present in the atmosphere as part of the Earth's carbon cycle (the natural circulation of carbon among the atmosphere, oceans, soil, plants, and animals).
- 8.2: An Automobile Factory
- Whenever you are making something, whether in a factory or at home, the amount of raw material available is an important consideration. We can use our "recipe" for making our desired product to determine how much can be produced from the raw materials on hand and which material will run out first.
- 8.3: Stoichiometry and the Molar Interpretation
- Chemical equations provide us with the relative number of particles and moles that react to form products. In this section you will explore the quantitative relationships that exist between the quantities of reactants and products in a balanced equation. This is known as stoichiometry. Stoichiometry, by definition, is the calculation of the quantities of reactants or products in a chemical reaction using the relationships found in the balanced chemical equation.
- 8.4: Molar Ratios and Mole-to-Mole Conversions
- Previously, you learned that the coefficients in front of the chemical formulas in a balanced chemical equation represent the numbers of moles of each substance reacted or formed. These coefficients can be used to construct conversion factors, known as molar ratios, to convert from moles of one substance to moles of another substance in the balanced chemical equation.
- 8.5: Mass-to-Mass Conversions
- We have used balanced equations to set up molar ratios that we can use as conversion factors to answer stoichiometric questions, such as how many moles of substance A react with so many moles of reactant B. We can extend this technique even further. Recall that we can relate a molar amount to a mass amount using molar mass. We can use that ability to answer stoichiometry questions in terms of the masses of a particular substance, in addition to moles.
- 8.6: Limiting Reactants and Excess Reactants
- Often reactants are present in mole ratios that are not the same as the ratio of the coefficients in the balanced chemical equation. As a result, one or more of them will not be used up completely, but will be left over when the reaction is completed. The limiting reactant is the reactant that is entirely consumed in a reaction. The excess reactant is the one that is left over when the reaction is done. The amount of product formed by the limiting reactant is the theoretical yield.
- 8.7: Theoretical Yield and Percent Yield
- Chemists need a measurement that indicates how successful a reaction has been. This measurement is called the percent yield.