The H atom balance was upset by this change, but it is easily reestablished by changing the coefficient for the H 2 product to 2. These coefficients yield equal numbers of both H and O atoms on the reactant and product sides, and the balanced equation is, therefore:. Write a balanced equation for the reaction of molecular nitrogen N 2 and oxygen O 2 to form dinitrogen pentoxide. Though nitrogen is balanced, changes in coefficients are needed to balance the number of oxygen atoms. To balance the number of oxygen atoms, a reasonable first attempt would be to change the coefficients for the O 2 and N 2 O 5 to integers that will yield 10 O atoms the least common multiple for the O atom subscripts in these two formulas.
The N atom balance has been upset by this change; it is restored by changing the coefficient for the reactant N 2 to 2.
The numbers of N and O atoms on either side of the equation are now equal, and so the equation is balanced. Write a balanced equation for the decomposition of ammonium nitrate to form molecular nitrogen, molecular oxygen, and water. Hint: Balance oxygen last, since it is present in more than one molecule on the right side of the equation. It is sometimes convenient to use fractions instead of integers as intermediate coefficients in the process of balancing a chemical equation.
For example, consider the reaction of ethane C 2 H 6 with oxygen to yield H 2 O and CO 2 , represented by the unbalanced equation:. Following the usual inspection approach, one might first balance C and H atoms by changing the coefficients for the two product species, as shown:.
A conventional balanced equation with integer-only coefficients is derived by multiplying each coefficient by Finally with regard to balanced equations, recall that convention dictates use of the smallest whole-number coefficients. Although the equation for the reaction between molecular nitrogen and molecular hydrogen to produce ammonia is, indeed, balanced,.
Dividing each coefficient by the greatest common factor, 3, gives the preferred equation:. The physical states of reactants and products in chemical equations very often are indicated with a parenthetical abbreviation following the formulas. Common abbreviations include s for solids, l for liquids, g for gases, and aq for substances dissolved in water aqueous solutions , as introduced in the preceding chapter.
These notations are illustrated in the example equation here:. This equation represents the reaction that takes place when sodium metal is placed in water. The solid sodium reacts with liquid water to produce molecular hydrogen gas and the ionic compound sodium hydroxide a solid in pure form, but readily dissolved in water. Given the abundance of water on earth, it stands to reason that a great many chemical reactions take place in aqueous media. When ions are involved in these reactions, the chemical equations may be written with various levels of detail appropriate to their intended use.
To illustrate this, consider a reaction between ionic compounds taking place in an aqueous solution. When ionic compounds dissolve in water, they may dissociate into their constituent ions, which are subsequently dispersed homogenously throughout the resulting solution a thorough discussion of this important process is provided in the chapter on solutions. Ionic compounds dissolved in water are, therefore, more realistically represented as dissociated ions, in this case:.
Unlike these three ionic compounds, AgCl does not dissolve in water to a significant extent, as signified by its physical state notation, s. Explicitly representing all dissolved ions results in a complete ionic equation. In this particular case, the formulas for the dissolved ionic compounds are replaced by formulas for their dissociated ions:.
These spectator ions —ions whose presence is required to maintain charge neutrality—are neither chemically nor physically changed by the process, and so they may be eliminated from the equation to yield a more succinct representation called a net ionic equation :. Following the convention of using the smallest possible integers as coefficients, this equation is then written:.
This net ionic equation indicates that solid silver chloride may be produced from dissolved chloride and silver I ions, regardless of the source of these ions.
When carbon dioxide is dissolved in an aqueous solution of sodium hydroxide, the mixture reacts to yield aqueous sodium carbonate and liquid water. Write balanced molecular, complete ionic, and net ionic equations for this process. Begin by identifying formulas for the reactants and products and arranging them properly in chemical equation form:. Balance is achieved easily in this case by changing the coefficient for NaOH to 2, resulting in the molecular equation for this reaction:.
The two dissolved ionic compounds, NaOH and Na 2 CO 3 , can be represented as dissociated ions to yield the complete ionic equation:. Diatomic chlorine and sodium hydroxide lye are commodity chemicals produced in large quantities, along with diatomic hydrogen, via the electrolysis of brine, according to the following unbalanced equation:.
Chemical equations are symbolic representations of chemical and physical changes. How do chemical equations illustrate that atoms are conserved? How can I know the formula of the reactants and products with chemical equations? How can I balance this chemical equations? Potassium metal and chlorine gas combine to form How many types of chemical reactions exist? How can a chemical equation be made more informative? How can I balance this equation?
See all questions in Chemical Equations. Stoichiometry is exactly that. It is the quantitative relation between the number of moles and therefore mass of various products and reactants in a chemical reaction. Chemical reactions must be balanced, or in other words, must have the same number of various atoms in the products as in the reactants.
If a chemical reaction is not balanced, no information about the relationship between products and reactants can be derived. So the first thing to do when you see a chemical reaction is to balance it.
We balance reactions by adding coefficients in front of the reactants and products. These coefficients are the stoichiometric coefficients.
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