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Chemical Formulas

A chemical reaction is described by an equation that contains the reactants on the left and the products on the right. Often times the phases of the participants (solid, liquid, or gas) and the amount of each substance is included.

For example, hydrogen gas and oxygen gas can be combined to produce water. The reaction is shown below:

The previous equation balanced would be:

Theoretical Yield

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The theoretical yield is the amount of products that can be formed in a reaction given the initial quantities of reactants. The theoretical yield is a purely mathematical quantity and does not rely on previous laboratory experimentation. In reality, many factors prevent the production of the quantity of products predicted by the theoretical yield. Side reactions may yield different products. The reactants may not completely react, or products may be lost in an extraction and purification process.

Theoretical Yield

In this example, if there is present only one mole of hydrogen and one mole of oxygen molecules, then the theoretical yield of water molecules will be half a mole.

For an equation to be truly balanced, everything needs to accounted for. Usually this is just a count of the atoms, but in a certain class of reactions, redox reactions, electrons are transferred from one atom to another. In these reactions, an overall electron count, in addition to an atom count, needs to be considered to properly balance the equation. When there is energy released or absorbed in the form of heat, then it needs to be taken into account as well.

Limiting Reagents

Molecules react with each other in very specific amounts described by the reaction's formula. The proportions of one reagent that react with another reagent are different based on each reaction, but are always in whole number proportions. In the previous reaction, two molecules of hydrogen gas reacted with one molecule of oxygen gas.

In calculating the amount of products produced during a reaction, it is vital to determine which reactant is the limiting reagent. Once it is identified, all further calculations are based on how much of it there is.

When there is a limiting reagent, the amount of products produced is limited too. If there is only half as much of one reagent as needed, then only has as much product will be produced.

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What You'll Learn in this Lesson

In this section, the nature of an ionic bond will be explained and compared to the natures of covalent and metallic bonds. We will discuss how to use the relative electronegativities of two atoms to determine whether they will join in an ionic bond or not and how their electron affinities and ionization energies determine how much energy is required to create the bond. Coulomb's Law will be introduced to describe how the strength of various ionic bonds can be compared, and we will cover how ionic bonds behave in different environments. Finally, we will cover the naming of ionically bonded molecules and mention a few polyatomic ions that are covalently bonded but interact in ionic bonds.

 

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