Which compound stoichiometry and limiting reagent

There are more hydrogen, nitrogen, and oxygen atoms on the product side. Therefore, the equation needs to be balanced. Balancing an equation is an iterative process that requires adding coefficients to each side until the numbers become equal. There are several approaches to balance a chemical equation.

One approach uses a table to visualize the numbers and a bit of trial and error. Since there is only one hydrogen atom on the reactant side but eight hydrogen atoms on the product side, multiplying the compound containing the nitrogen on the reactant side by eight would balance hydrogen. The second row in the new table reflects this change to the number of atoms.

Next, to increase the number of nitrogens on the product side, multiplying the product Cu NO 3 2 by three would raise the number of nitrogen atoms from three to seven.

The number of nitrogen atoms is not balanced yet, but there are still coefficients for one reactant and one product to consider. If there are two molecules of NO produced, this adds one more nitrogen atom and one more oxygen atom to the product side, balancing these two species with the reactant side. The only atom left unbalanced now is copper. Increasing the number to three copper atoms on the reactant side balances the equation. Balancing the equation is also essential for determining the limiting reactant because the coefficient of the compounds is used to calculate how much product is produced by each reactant product yield.

From this quantity, the reactant producing the least amount of product is considered the limiting reactant--which is completely consumed in the reaction and therefore limits the total amount of product generated. This calculated quantity also represents the theoretical yield of the reaction, which is needed to calculate the percent yield. If a recipe calls for 1 cup of peanut butter, and 3 cups of sugar to make 12 cookies and you start with 3 cups of peanut butter and 12 cups of sugar based on the amount of peanut butter you have you could make 36 cookies but based on the amount of sugar you have you could make 48 cookies.

In this case peanut butter is our limiting reactant and we can only make 36 cookies but will have 3 cups of sugar left over when we are finished which means it is our excess reactant. The idea behind limiting and excess reagents is identical to what we did above with the baking except we are dealing with elements instead of ingredients.

Four moles of propane reacts with ten moles of oxygen. How much carbon dioxide will be produced from this reaction? The first step in determining the excess and limiting reactants is to have your equation fully balanced so you can see the stoichiometric ratios between the different compounds.

The next step is to determine the conversion factor to multiply the moles of each element by to find the amount of product it will produce. To find the conversion factor simply divide the element by its coefficient and then multiply by the coefficient of the element you wish to know the amount of moles of. Well, the same number of moles of carbon monoxide that we're using up. It's a one-to-one ratio. So we're going to produce And so let me write that a year.

So if I have Well, I have to multiply this times a certain number of grams per mole so that we can cancel out the moles or essentially the molar mass of methanol, and to figure out the molar mass of methanol, we'll get our calculator out again. So we have four hydrogens here. So four times 1. And then to that, we're going to add the molar mass of carbon 'cause we have one carbon plus And let's see, we will round to the hundreds place because our oxygen and carbon molar mass is only went to the hundreds place here, so So we have And let's see, we have three significant figures, four, so I'll round to three.

So approximately grams of methanol, grams of CH3OH. Now the next question is, what's the mass of hydrogen that we have leftover?

Try to keep the same drop size. Add 9 drops of 0. Note: To prevent contamination of the solution in the pipet, do not touch the pipet to the solutions in the well plate.

Mix the contents of each filled well by gently swirling the plate, being careful not to spill any of the contents. Allow about 5 min for precipitate to settle. Observe the solids in each of the wells and visually determine which well has the most precipitate. If 2 wells are difficult to rank, redo those.

Since the reactant solutions have the same concentrations molarities , the volume ratio of the reactants is the same as the mole ratio. On this drop ratio basis, determine ratio of the coefficients of the reactants. Repeat steps 1 through 5 in the procedure above using 0. Once the students complete the lab, a guided discussion of their results helps reinforce the concept of a limiting reactant. Have the students reach a consensus on which well in each reaction produced the maximum amount of precipitate.

In these wells, the reactants should be in the same ratio as the coefficients in the balanced equation. Ask which reactant is limiting and which reactant is in excess in the other wells.

If the students are familiar with double-displacement reaction, they can use the ratio between the reactants to write a complete balanced equation for the reaction. If they are familiar with solubility rules, have them predict which compound is the precipitate and add physical states to their reactions. A discussion of which variables are held constant in the lab, why they are held constant, and sources of error helps them understand experimental design and evaluation of results.

Limiting reactants is often a difficult concept for students to understand but allowing students to perform simple reactions helps reinforce the concept.

In terms of practical applications, industrial chemists run reactions to produce a compound to sell. Engage the students in a discussion about why it might be economical to have the reactants in the correct mole ratio, how it might be easier to separate and purify the product without excess reactant present, and the possibility of recycling any excess reactant.

Ask students for other examples of a limiting reactant or resource in their lives. Try another activity. Neither Achieve nor the lead states and partners that developed the Next Generation Science Standards were involved in the production of, and do not endorse, these products. We use cookies to provide you with a great user experience. By using our site, you accept our use of cookies. You can review our cookie and privacy policy here.

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