Giới Thiệu · Stoichiometry
Stoichiometry is an ultimate tool for balancing chemical reactions, finding molar masses, moles and actual masses of reactants and products based on their chemical formulas, stoichiometric coefficients and any quantitative data provided. It is enough to provide initial or final mass or moles of one of the reaction component, to calculate all required and obtained masses and moles of all components. Limiting reagent will be found based on the reaction stoichiometry.
For chemical reaction: aA + bB -> cC + dD,
the components will only react in a defined ratios. Thus, every "a" moles of compound "A" will need "b" moles of compound "B", to produce "c" moles of "C". If more "B" will be added than it is required, then all spare amount of "B" will be left unconsumed. In such a case compound "A" will be called a "Limiting Reagent", as its "small" amount limits or stops reaction before all other reagents are consumed.
While mathematics behind the stoichiometry is rather simple and straightforward, the continuous need to convert moles obtained from balancing chemical reaction to actual masses to be weighed, routinely casts burden upon students and lab workers. In order to facilitate and significantly accelerate the process, the Stoichiometry application has been developed. Let's consider the working example:
Example 1:
How many moles of HCl are needed in order to obtain 2.0 g of FeCl3, in the reaction:
HCl + FeI2 + HCl -> FeCl3 + ICl + H20
The first step is balancing chemical reaction and finding molar masses, since moles-mass conversion is needed. All is done automatically by pressing the orange arrow connecting reagents and products (the screenshot is provided):
5HClO3 + 4FeI2 + 25HCl -> 4FeCl3 + 13ICl + 15H20,
The next step is to find the moles of FeCl3 from the mass (2.0 g), and then convert them to moles of HCl based on 4:25 ratio obtained from the balanced reaction. Stoichiometry application provides data table that comprised of masses and moles rows for data available before reaction initiated (coloured blue), and data rows for component amounts that obtained or left after the reaction is accomplished (coloured violet). When the direction of calculation arrow, that is located between the initial and final data rows, is turned downwards the final masses and moles are calculated from the initially provided amounts of reactant and products, and when it turned upwards, reactants and products amounts that would be required to achieve the provided final state are calculated. The later is exactly matches our situation, as we need to find the initial amount of HCl from the final, known FeCl3 mass. So we press the arrow to turn it upwards, set the FeCl3 mass to the final mass field and press calculate button to automatically fill the table with all masses and moles for all components. Apparently, 77.07 mmoles of HCl are required to get 2.0 g of FeCl.
Example 2:
Using the same reaction:
5HClO3 + 4FeI2 + 25HCl -> 4FeCl3 + 13ICl + 15H20,
Find out the limiting reagent, if 3.0 grams of each reactant have been mixed initially.
Solution using Stoichiometry application: The direction arrow should be turned downwards, since initial data is provided for calculations. Next, masses should be set for all reagents in blue mass fields and then pressing the calculate button populates the final violet cells for reactants that left and products that are obtained.
The application alerts on FeI2 as a limiting reagent, and indeed all 9.687 mmoles of the FeI2 are consumed, while other reagents are partially left unused.
Important points:
Charge, if exist must be provided as well, separated by coma: Na,+ .
