What is the difference between reaction stoichiometry and composition stoichiometry

There are two levels of stoichiometry in chemistry. The first is composition stoichiometry. That is the one where you were looking at ratios of atoms that make molecules or formula units.

The other one is reaction stoichiometry where are you are looking at how many moles of a compound will react with how many moles of another compound to make some sort of chemical product.

In order to make stoichiometry work for you, you must have the correct chemical formulas for each substance and a correctly balanced chemical reaction. Once you have your formulas and reactions in place, stoichiometry is really just a method of scaling things up or scaling things down. It is one of the the primary compounds in the ore that is mined so that we can produce iron, and more importantly - steel. So here is the question: how many kilograms of iron can be produced from 1.

Answer: The first thing you should notice is the question is completely in mass units so we can answer this question by simply staying in mass units of iron oxide or magnetite. We first get its molar mass by taking the atomic weight of iron times three and the atomic weight of oxygen times four and adding the results. For instance, we can say that one molecule of glucose has 6 carbon atoms, or we can say, equivalently, that one mole of glucose has 6 moles of carbon atoms.

And that, in a nutshell, is composition stoichiometry. Reaction stoichiometry allows us to determine the amount of substance that is consumed or produced by a reaction.

The following video considers the first part of this: how much of a reactant is consumed in a chemical reaction. Product formation is discussed elsewhere. Will have to use factor label method what you want goes on top, what you wanna get rid of goes on bottom c. Mass- mole.

Mass - Mass. Volume to Volume. Let us consider an example to understand the theory behind reaction stoichiometry. The reaction between an alkali metal and water produces heat energy, hydroxide of the metal, and hydrogen gas.

Here, the details we know are the mass of alkali metal used and amount of water used for the reaction. After the completion of the reaction, the amount of hydrogen gas can be collected and using its volume, the moles of hydrogen gas evolved can be calculated.

Therefore, assuming that all the alkali metal reacted with water, we can get the ratio between reactants and products involved in this reaction. This is the reaction stoichiometry of alkali metal in water reaction. The key difference between composition and reaction stoichiometry is that the composition stoichiometry refers to the atomic make-up of a chemical compound, whereas reaction stoichiometry refers to the amount of compounds consumed or produced during a chemical reaction.

While composition stoichiometry gives the ratio between atoms of each chemical element present in a compound, reaction stoichiometry gives the ratio between reactants and products involved in a particular reaction. Stoichiometry is a method of quantitative analysis of a chemical compound or a chemical reaction. Mass to mass conversions : A chart detailing the steps that need to be taken to convert from the mass of substance A to the mass of substance B.

This can be illustrated by the following example, which calculates the mass of oxygen needed to burn The balanced equation is:.

Because there is no direct way to compare the mass of butane to the mass of oxygen, the mass of butane must be converted to moles of butane:. With the number of moles of butane equal to 54 grams, it is possible to find the moles of O 2 that can react with it. This last equation shows that 6. The molar amount of O 2 can now be easily converted back to grams of oxygen:. In summary, it was impossible to directly determine the mass of oxygen that could react with But by converting the butane mass to moles 0.

Using the molar amount of oxygen, it is then possible to find the mass of the oxygen g. Stoichiometry: Grams to Grams — YouTube : This video shows how to determine the grams of the other substances in the chemical equation if the grams of one of the substances is known. The mole is the universal measurement of quantity in chemistry.

However, the measurements that researchers take every day provide answers not in moles but in more physically concrete units, such as grams or milliliters. Therefore, scientists need some way of comparing what can be physically measured to the amount of measurement they are interested in: moles.

Because scientists of the early 18th and 19th centuries could not determine the exact masses of the elements due to technology limitations, they instead assigned relative weights to each element.

From this scale, hydrogen has an atomic weight of 1. Multiplying by the molar mass constant ensures that the calculation is dimensionally correct because atomic weights are dimensionless.

The molar mass value can be used as a conversion factor to facilitate mass-to-mole and mole-to-mass conversions. After the molar mass is determined, dimensional analysis can be used to convert from grams to moles. Mass and mole conversions : The mass and molar quantities of a substance can be easily interconverted by using the molecular weight as a conversion factor.

For example, convert 18 grams of water to moles of water. Stoichiometry, Grams to Moles — YouTube : This video describes how to determine the number of moles of reactants and products if given the number of grams of one of the substances in the chemical equation. The reagent that limits how much product is produced the reactant that runs out first is known as the limiting reagent.

In a chemical reaction, the limiting reagent, or limiting reactant, is the substance that has been completely consumed when the chemical reaction is complete.

The amount of product produced by the reaction is limited by this reactant because the reaction cannot proceed further without it; often, other reagents are present in excess of the quantities required to to react with the limiting reagent. From stoichiometry, the exact amount of reactant needed to react with another element can be calculated. However, if the reagents are not mixed or present in these correct stoichiometric proportions, the limiting reagent will be entirely consumed and the reaction will not go to stoichiometric completion.

Limiting reagent : The limiting reagent in a reaction is the first to be completely used up and prevents any further reaction from occurring. In this reaction, reactant B is the limiting reagent because there is still some left over A in the products.

Therefore, A was in excess when B was all used up. One way to determine the limiting reagent is to compare the mole ratio of the amount of reactants used.

This method is most useful when there are only two reactants. One reactant A is chosen, and the balanced chemical equation is used to determine the amount of the other reactant B necessary to react with A. If the amount of B actually present exceeds the amount required, then B is in excess, and A is the limiting reagent. If the amount of B present is less than is required, then B is the limiting reagent.

To begin, the chemical equation must first be balanced. The law of conservation states that the quantity of each element does not change over the course of a chemical reaction. Therefore, the chemical equation is balanced when the amount of each element is the same on both the left and right sides of the equation. Next, convert all given information typically masses into moles, and compare the mole ratios of the given information to those in the chemical equation.

For example: What would be the limiting reagent if 75 grams of C 2 H 3 Br 3 reacted with It is then possible to calculate how much C 2 H 3 Br 3 would be required if all the O 2 is used up:. This demonstrates that 0. Since there is only 0. Another method of determining the limiting reagent involves the comparison of product amounts that can be formed from each reactant. This method can be extended to any number of reactants more easily than the previous method. Again, begin by balancing the chemical equation and by converting all the given information into moles.

Then use stoichiometry to calculate the mass of the product that could be produced for each individual reactant.