Stoichiometry percent yield

Conversion Factors from a Chemical Equation Mass-Mass Stoichiometry Percent Yield Limiting Reactants ... 

The amount of a product obtained from a reaction is often reported as a yield. The amount of product predicted by stoichiometry is the theoretical yield, whereas the amount actually obtained is the actual yield. The percent yield is the percentage of the theoretical amount that is actually obtained ... 

The problem asks for a yield, so we identify this as a yield problem. In addition, we recognize this as a limiting reactant situation because we are given the masses of both starting materials. First, identify the limiting reactant by working with moles and stoichiometric coefficients then carry out standard stoichiometry calculations to determine the theoretical amount that could form. A table of amounts helps organize these calculations. Calculate the percent yield from the theoretical amount and the actual amount formed. 

Reaction stoichiometry Limiting reactants Percent yield... 

In this chapter, you learned how to balance simple chemical equations by inspection. Then you examined the mass/mole/particle relationships. A mole has 6.022 x 1023 particles (Avogadro s number) and the mass of a substance expressed in grams. We can interpret the coefficients in the balanced chemical equation as a mole relationship as well as a particle one. Using these relationships, we can determine how much reactant is needed and how much product can be formed—the stoichiometry of the reaction. The limiting reactant is the one that is consumed completely it determines the amount of product formed. The percent yield gives an indication of the efficiency of the reaction. Mass data allows us to determine the percentage of each element in a compound and the empirical and molecular formulas. 

The amount of product actually formed in a reaction divided by the amount theoretically possible and multiplied by 100% is called the reaction s percent yield. For example, if a given reaction could provide 6.9 g of a product according to its stoichiometry, but actually provides only 4.7 g, then its percent yield is 4.7/6.9 X 100% = 68%. 

A stainless steel reaction vessel of 10 cc volume was charged with 0.56 part sodium nitrite, 0.8 part of distilled water and 0.34 part sodium bicarbonate. The vessel was cooled with liquid nitrogen under a blanket of argon to assure lack of air moisture condensation in the vessel. To the chilled vessel was added 3.9 parts of liquid methyl chloride (measured and weighed at—77° C. with density taken at 1.1). 3.5 parts of the added methyl chloride was excess over that required for stoichiometry. The vessel was sealed and heated at 75° C. for 4 hours with agitation. The resultant material was analyzed by conventional gas chromatographic analysis and showed that nitromethane was obtained in 57 percent yield. The selectivity to nitromethane was 74 percent based on the sodium nitrite. 

Example 10.4 shows how percent yield calculations can be combined with equation stoichiometry problems. 

Stoichiometry is the quantitative study of products and reactants in chemical reactions. Stoichiometric calculations are best done by expressing both the known and unknown quantities in terms of moles and then converting to other units if necessary. A limiting reagent is the reactant that is present in the smallest stoichiometric amount. It limits the amount of product that can be formed. The amount of product obtained in a reaction (the actual yield) may be less than the maximum possible amount (the theoretical yield). The ratio of the two is expressed as the percent yield. 

The percent yield is the amount of K produced compared to complete conversion since the stoichiometry of reaction (2) is one-to-one, we can write ... 

Reflect and t ply Why can the Edman degradation not be used effectively with very long peptides Hint Think about the stoichiometry of the peptides and the Edman reagent and the percent yield of the organic reactions involving them. 

Chemical stoichiometry is the area of study that considers the quantities of materials in chemical formulas and equations. Quite simply, it is chemical arithmetic. The word itself is derived from stoicheion, the Greek word for element and metron, the Greek word for measure. When based on chemical formulas, stoichiometry is used to convert between mass and moles, to calculate the number of atoms, to calculate percent composition, and to interpret the mole ratios expressed in a chemical formula. Most topics in chemical arithmetic depend on the interpretation of balanced chemical equations. Mass/mole conversions, calculation of limiting reagent and percent yield, and various relationships among reactants and products are commonly included in this topic area. 

Let s return to our pancake analogy to xmderstand two more concepts important in reaction stoichiometry limiting reactant and percent yield. Recall our pancake... 

CIA Demonstration Self-Inflating Hydrogen Balloons Theoretical Yield and Percent Yield A Problem Involving the Combined Concepts of Stoichiometry... 

We can choose to make this a two-part problem. We are given the actual yield. The stoichiometry problem for finding MgO must be based on theoretical yield. What is our link between actual and theoretical yield Percent yield gives us the conversion factor 81.3 g (act)/100 g (theo). First we will find the theoretical yield from the actual yield then we will calculate the amount of reactant by stoichiometry. 

Mass stoichiometry 2. Thermochemical stoichiometry 3. Limiting reactant 4. Mass stoichiometry 5. Percent yield 6. Thermochemical stoichiometry 7. Limiting reactant 8. Percent yield... 

When you use stoichiometry to calculate the amount of product formed in a reaction, you are calculating the theoretical yield of the reaction. The theoretical yield is the amount of product that forms when all the limiting reactant reacts to form the desired product It is the maximum obtainable yield, predicted by the balanced equation. In practice, the actual yield— the amount of product actually obtained from a reaction—is almost always less than the theoretical yield. Th e are many reasons for the difference between the actual and theoretical yields. For instance, some of the reactants may not react to form the desired product. They may react to form different products, in something known as side reactions, or they may simply remain unreacted. In addition, it may be difficult to isolate and recover all the product at the end of the reaction. Chemists often determine the efficiency of a chemical reaction by calculating its percent yield, which tells what percentage the actual yield is of the theoretical yield. It is calculated as follows ... 

Other Practical Matters in Reaction Stoichiometry— Stoichiometric calculations sometimes involve additional factors, including the reaction s actual yield, the presence of by-products, and how the reaction or reactions proceed. For example, some reactions yield exactly the quantity of product calculated—the theoretical yield. When the actual yield equals the theoretical yield, the percent yield is 100%. In some reactions, the actual yield is less than the theoretical, in which case the percent yield is less than 100%. Lower yields may result from the formation of by-products, substances that replace some of the desired product because of reactions other than the one of interest, called side reactions. Some stoi-... 

Transition State Models. The stoichiometry of aldehyde, dialkylzinc, and the DAIB auxiliary strongly affects reactivity (Scheme 9) (3). Ethylation of benzaldehyde does not occur in toluene at 0°C without added amino alcohol however, addition of 100 mol % of DAIB to diethylzinc does not cause the reaction either. Only the presence of a small amount (a few percent) of the amino alcohol accelerates the organometallic reaction efficiently to give the alkylation product in high yield. Dialkyl-zincs, upon reaction with DAIB, eliminate alkanes to generate alkylzinc alkoxides, which are unable to alkylate aldehydes. Instead, the alkylzinc alkoxides act as excellent catalysts or, more correctly, catalyst dimers (as shown below) for reaction between dialkylzincs and aldehydes. The unique dependence of the reactivity on the stoichiometry indicates that two zinc atoms per aldehyde are responsible for the alkyl transfer reaction. 

It is a simple calculation based on the stoichiometry of the reaction, but does not account for solvents, reagents, reaction yield and reactant molar excess. Atom economy is one of the 12 principles of green chemistry [36]. The larger the number, the higher the percent of all reactants appearing in the product. 

Figure 4. Yield of HCN, expressed as percent N> converted, as a function of input stoichiometry. Solid lines show maximum yield predicted by thermodynamic equilibrium. Data points show experimental results from the plasma reactor Ar flow rate 42 std. cc./sec., total reagent flow rate 2 std. cc./sec., net power 3.5 kw. Reactor pressure identified with key. Points labeled X from plasma jet studies...

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