Balancing an Equation

And suppose you then wanted to balance the equation for the reaction between glucose and ammonium perchlorate. The key to balancing an equation by the Pyro Valence method is to remanber that the oxidizing valences will equal the reducing valences, or the sum of the valences wiU equal zero. 

To balance an energetic equation, determine the coefficients (smallest whole number ratio) that will produce equal valences. 

For ammonium perchlorate, or AP (-5) and glucose (+24), you will need twenty-four APs and five glucoses in the balanced equation. There are no smaller factors for the numbers 24 and 5. Put these coefficients in for the reactants, and you ve balanced the equation. You can then work out how many moles of each product will form, if you so desire. 

Note This method assumes that all N winds up as N2, and all Cl winds up as HCl. All the C atoms in the fuel are assumed to go to CO2, all the H atoms go to H2O or HCl, and all the N atoms become N2. Upon inspection, the equation is balanced  

Note The Pyro Valence method works equally well if one wishes to calculate the stoichiometric mixture for a composition where carbon monoxide (CO) is the assumed product formed by the carbon atoms in the fuel. To do this, use +2 as the valence for carbon in the calculations, and the net valence for glucose will be +12. The balanced equation will be 

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Electrokinetics. The first mathematical description of electrophoresis balanced the electrical body force on the charge in the diffuse layer with the viscous forces in the diffuse layer that work against motion (6). Using this force balance, an equation for the velocity, U, of a particle in an electric field... 

Frequently, when you are asked to balance an equation, the formulas of products and reactants are given. Sometimes, though, you will have to derive the formulas, given only the names (Example 3.8). 

In some cases, the stoichiometric coefficients needed to balance an equation are easy to determine. For example, let s consider the reaction in which hydrogen and oxygen gases combine to form water. We start by summarizing the qualitative information as a skeletal equation ... 

Component mass balance An equation relating the rate of change of the mass of a component in the system to the rates of inflow, outflow, and chemical reaction. See Eq. (2). 

Biochemical reactions are interesting but they are not magic . Individual chemical reactions that comprise a metabolic pathway obey, obviously, the rules of organic chemistry. All too often students make fundamental errors such as showing carbon with a valency of 3 or 5, or failing properly to balance an equation when writing reactions. Furthermore, overall chemical conversions occur in relatively small steps, that is there are usually only small structural changes or differences between consecutive compounds in a pathway. 

To balance an equation, you use coefficients to alter the number of moles of reactants and/or products so the mass on one side of the equation equals the mass on the other side. A coefficient is simply a number that precedes the symbol of an element or compound, multiplying the number of moles of that entire compound within the equation. Coefficients are different from subscripts, which multiply the number of atoms or groups within a compound. Consider the following ... 

When you balance an equation, you change only the coefficients. Changing subscripts alters the chemical compounds themselves, and you can t do that. If your pencil were equipped with an electrical shocking device, that device would activate the moment you attempted to change a subscript while balancing an equation. 

When substances—the reactants—react to form new substances—the products—we say that a chemical reaction has occurred. A chemical equation is a statement of such an event in which the formulas of the reactants are on the left, followed by a right-pointing arrow and then the formulas of the products. In a balanced equation, coefficients specify the number of molecules (or formula units) of each species involved. The coefficients must satisfy Dalton s requirement that atoms are not created or destroyed in a chemical reaction. There is no fixed procedure for balancing an equation. Although a systematic algebraic approach is in principle possible, a trial-and-error approach often works. 

To begin to balance an equation, you can add numbers in front of the appropriate formulas. The numbers that are placed in front of chemical formulas are called coefficients. They represent how many of each atom, molecule, or formula unit take part in each reaction. For example, if you add a coefficient of 2 to NaCl in the equation in Figure 4.2, you indicate that two formula units of NaCl are produced in the reaction. Is the equation balanced now As you can see by examining Figure 4.3, it is not. The chlorine atoms are balanced, but now there is one sodium atom on the left side of the equation and two sodium atoms on the right side. 

You cannot balance an equation by changing any of the chemical formulas. The only way to balance a chemical equation is to put the appropriate numerical coefficient in front of each compound or element in the equation. 

If you are in doubt about writing simple chemical formula or how to balance an equation, see formula and balancing chemical equations in the Glossary. If you are uncertain of any symbol for an element then refer to the lists in the Appendies. 

Step by step you can now balance an equation. Try this example ... 

One of the problems encountered by students just learning to balance equations is that the absence of a coefficient in a balanced equation means a coefficient of 1, but the absence of a coefficient before the equation is fully balanced might mean that this substance has not yet been considered. To avoid any confusion, we can place a question mark before each formula when we start to balance an equation. (After we have had a lot of practice, we will not need to use the question marks.)... 

Practice Problem 8.4 Balance an equation for the reaction of ammonium sulfide with copper(ll) chloride to yield copper(ll) sulfide and ammoninm chloride. ... 

Complete and balance an equation for the reaction of zinc metal and oxygen gas. 

To balance an equation— that is, to make the numbers of atoms of each of the elements the same on both sides of the equation—we place coefficients in front of each formula in the equation. The state of each substance may be indicated as gas (g), liquid ( ), solid (s), or solute in aqueous solution (aq) (Section 8.2). 

Essentially, most problems involving mole calculations are as simple as the one in Example 10.2. A problem may seem more difficult if we have to write and balance an equation, but we learned how to do that in Chapter 8. 

Complete and balance an equation for the reaction in which cyanate ion (CNO ) is oxidized to CO2 and N03 by Mn04, in which two elements in the same chemical species are oxidized. (Hint The carbon to nitrogen ratio is set by the formula of CNO. )... 

This description makes the process of balancing an equation seem very long-winded, but as you get used to doing more of them, it gets faster. Now try the supplementary questions on this topic for extra practice. You ll find them after the answers to the diagnostic test. Some of them may not need changing in order to be balanced - look at each example logically and add up the number of atoms on each side first. Don t just jump to conclusions ... 

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