Theoretical yield The amount

Many conditions are required for a chemical reaction to proceed. Conditions such as heat, light, and pressure must be just right for a reaction to take place. Furthermore, the reaction may proceed very slowly. Some reactions occur in a fraction of a second, while others occur very slowly. Consider the difference in the reaction times of gasoline igniting in a car s cylinder versus the oxidation of iron to form rust. The area of chemistry that deals with how fast reactions occur is known as kinetics (Chapter 12). Finally, not all reactions go to completion. The amount of product produced based on the chemical equation is known as the theoretical yield. The amount actually obtained expressed as a percent of the theoretical is the actual yield. In summary, it s best to think of a chemical equation as an ideal representation of a reaction. The equation provides a general picture of the reaction and enables us to do theoretical calculations, but in reality reactions deviate in many ways from that predicted by the equation. 

Theoretical yield The amount of a given product formed if all of the limiting reactant is consumed by the reaction. 

The amount of product produced when a reaction runs to completion is called the theoretical yield. The amount of actual product after a real experiment is the actual yield. As mentioned above, reactions often don t run to completion, and sometimes there are competing reactions that reduce the actual yield. Actual yield divided by the theoretical yield, times 100, gives the percent yield. 

Ternary compounds. Compounds consisting of three elements. (2.7) Theoretical yield. The amount of product predicted by the balanced equation when all of the limiting reagent has reacted. (3.10)... 

During a typical reaction, one substance (the limiting reactant) is used up, so it limits the amount of product that can form the other reac-tant(s) are in excess. The theoretical yield, the amount based on the balanced equation, is never obtained in the lab because of competing side reactions and physical losses. 

Up until now, we ve been optimistic about the amount of product obtained from a reaction. We have assumed that 100% of the limiting reactant becomes product, that ideal separation and purification methods exist for isolating the product, and that we use perfect lab technique to collect all the product formed. In other words, we have assumed that we obtain the theoretical yield, the amount indicated by the stoichiometrically equivalent molar ratio in the balanced equation. 

The quantity of product calculated to form when all of a limiting reactant is consumed is called the theoretical yield. The amount of product actually obtained, called the actual yield, is almost always less than (and can never be greater than) the theoretical yield. There are many reasons for this difference. Part of the reactants may not react, for example, or they may react in a way different from that desired (side reactions). In addition, it is not always possible to recover all of the product from the reaction mixture. The percent yield of a reaction relates actual and theoretical yields ... 

Theoretical yield. The amount of product calculated from the molar ratio in the balanced equation is the theoretical yield. But, there are several reasons why the theoretical yield is never obtained ... 

Actual yield. Given these reasons for obtaining less than the theoretical yield, the amount of product actually obtained is the actual yield. Theoretical and actual yields are expressed in units of amount (moles) or mass (grams). 

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