Determining the Limiting Reactant

STRATEGY First, the limiting reactant must be identified (Toolbox M.l). This limiting reactant determines the theoretical yield of the reaction, and so we use it to calculate the theoretical amount of product by Method 2 in Toolbox L.l. The percentage yield is the ratio of the mass produced to the theoretical mass times 100. Molar masses are j calculated using the information in the periodic table inside the front cover of this i book. 

Write a balanced chemical equation for the reaction. Find the amount (in mol) of each reactant, using its volume and concentration. Identify the limiting reactant. Determine the amount (in mol) of mercury(II) sulfide that forms. Calculate the mass of mercury(II) sulfide that precipitates. 

Often in reactions, the reactants are not consumed at exactly the same time. Then one of the reactants, called the limiting reactant, determines the maximum amount of product that can form. 

In situations such as this, a distinction is made between the excess reactant (Sb) and the limiting reactant, I2. The amount of product formed is determined (limited) by the amount of limiting reactant With 3.00 mol of 1 only 2.00 mol of Sbl3 is obtained, regardless of how large an excess of Sb is used. 

Determine the limiting reactant and the theoretical yield when... 

Make a table like the one above and determine the number of moles of acetic acid (HAc) and acetate ion (Ac-) after the reaction is complete. Since the stoichiometric ratios are 1 1, the limiting reactant is the one with the smaller number of moles. 

Collecting and Interpreting Data Based on your observations, describe which substance was the limiting reactant at the end of step 5, step 6, and step 7. How were you able to determine this ... 

The moles of NaOH consumed are determined from the amount of limiting reactant, H3P04. The moles and molarity of NaOH remaining is determined by subtraction. 

For the rest of the exercise, the plan is straightforward for the neutralization reaction between HN03 and NaOH, perform the limiting reactant problem. The pH is determined from the concentration of excess HN03 or NaOH. Each calculation is totally independent of the other calculations. 

After the equivalence point, the pH is determined directly from the concentration of excess NaOH since CH3COOH is now the limiting reactant. In the presence of the strong base, the effect of the weak base, CH3COO, derived from the salt is negligible. 

NAcc is the molar amount of the limiting reactant. From the MTSR the time to the maximum rate TMRaij can be determined as... 

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. 

In the examples above, one reactant was present in excess. One reactant was completely consumed, and some of the other reactant would be left over. The reactant that is used up first is called the limiting reactant (L.R.). This reactant really determines the amount of product being formed. How is the limiting reactant determined You can t assume it is the reactant in the smallest amount, since the reaction stoichiometry must be considered. There are generally two ways to determine which reactant is the limiting reactant ... 

In limiting-reactant problems, don t consider just the number of grams or even moles to determine the limiting reactant—use the mol/coefficient ratio. 

Step 4 Determine the number of moles of CUSO4 and NaOH that reacted. If necessary, determine the limiting reactant. Use the amount of limiting reactant to get AH of the reaction (in kj/mol). 

First of all, we have to determine which the limiting reactant is. The way to determine which reactant is limiting is to divide the moles of each reactant by the coefficient from the balanced equation associated with that reactant. The smallest number that comes out indicates which reactant is the limiting one. This reactant limits how much of every other species made or needed for the reaction. For A, this calculation gives 0.25 and for B, 0.5. Thus, A is the limiting reactant and the calculation of d, sR, and x should based on it. 

The amount of product is calculated by the same method used earlier for mole-to-gram stoichiometry problems. Start with the moles of the limiting factor because a limiting factor is defined as the reactant that limits or determines the amount of product that can be made. 

Although the previous equation signifies the importance of the diffusion characteristics of the reactant species, it cannot be used to describe adequately the rate of the reaction. The reason is that the concept of global concentrations for the riA and ng molecules is meaningless, since a unit volume cannot be conceived due to the local fluctuations of concentrations. Hence, the local concentrations of the reactants determine the rate of the reaction for diffusion-limited reactions. Accordingly, local density functions with different diffusion coefficients for the reactant species are used to describe the diffusion component of reaction-diffusion equations describing the kinetics of diffusion-limited reactions. 

The correct answer is (A). When you see two masses in a stoichiometry problem, you should be alerted that you are dealing with a limiting reactant problem. This problem will have two stages—the first is to determine the limiting reactant, and the second to determine the mass of the hydrogen gas. Before we do anything, we need to see the balanced equation for the reaction ... 

The reactant that is completely used up in a chemical reaction is called the limiting reactant. In other words, the limiting reactant determines how much product is produced. When the limiting reactant is used up, the reaction stops. In real-life situations, there is almost always a limiting reactant. 

Convert the given masses into moles. Use the mole ratios of reactants and products to determine how much ammonia is produced by each amount of reactant. The limiting reactant is the reactant that produces the smaller amount of product. 

First convert each reactant to moles and find the limiting reactant. Using the mole to mole ratio of the limiting reactant to the product, determine the number of moles of tetraphosphorus decaoxide that is expected. Convert this number of moles to grams. 

The reactant that is present in limiting quantity determines the extent of reaction that can take place. 

Because 7.72 mol O2 is available but only 5 mol is needed to react with 1 mol P4, O2 Is In excess and P4 is the limiting reactant. Use the moles of P4 to determine the moles of P4O10 that will be produced. 

To determine which is the limiting reactant, allow the output rate of NH3 to go to zero, i.e.,... 

The limiting reagent of a reaction is the reactant that runs out first. This reactant determines the amount of product formed, and any other reactants remain unconverted to product and are called excess reagents. 

Reaction 2.1.5 does not take place, rather it merely provides a relation between the reactants and the desired product. Usually, stoichiometric relations are used to determine the limiting reactant and the yield of the desirable products. 

The amount of F43P04 that can be formed will be determined by the amount of P4O10. Therefore, the P4O10 will be the limiting reactant. When the P4O10 is gone, the reaction stops, leaving an excess of water with the product. 

Referring to the reactants as A and B, to determine if reactant A is the limiting reactant, calculate the number of moles of B it will consume (a mole-to-mole conversion). 

We learn that 1.0 mole of Cr will consume 0.75 mole of 02, less than the amount of 02 in the starting mixture. There is in excess of 02, indicating Cr is the limiting reactant. All the chromium will be consumed, leaving the excess of 02. The number of moles of Cr consumed determines the number of moles of Cr203 produced. 

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