Stoichiometry

Introduction

Using stoichiometry, we can derive the number of reactants and products in a chemical equation that is in equilibrium. A ratio from the balanced equation is used here. To a large extent, all reactions are governed by a single variable: the amount of substance present. 

Stoichiometry is a useful tool for determining how much of a substance is actually present or required. The following are quantifiable concepts: 

• Reactants’ and Products’ mass
• Molecular weight
• Chemical equations
• Formulas

Stoichiometric Coefficients

Both sides of the equation have the same number of items in a balanced reaction. Chemical reactions have a number written before atoms, ions, and molecules called the “stoichiometric coefficient,” which ensures that each element on both the reactants and the product’s sides is equal in number. Even though the stoichiometric coefficients could be fractions, whole numbers are commonly used and are often preferred for their convenience and accuracy. Stoichiometry coefficients are useful because they establish the mole ratio of reactants and products. As part of the overall equation: 

2Na(s)+2HCl(aq)→2NaCl(aq)+H2(g)

Reaction Types 

It is possible to categorise reactions into different categories. 

• Combustion: In the combustion process, CO2 and H2O are formed as a result of the response of a chemical and O2. 
• Combination: The combination of two or more simple reactants into a more complex product is called a combination. 
• Decomposition is the process of breaking down complex substances into simpler ones. 
• One Displacement: When an element from one reactant swaps places with an element from the other to form two new reactants, it is a single displacement. 
• Double displacement :To put it simply, two elements from one reactant were exchanged for two from the other to create a new reaction. 
• Reactions in which acid and base react to form salt and water are called acid-base reactions.

Reactions and Mole Ratios that are in balance 

The number of atoms and molecules in a very small amount of a substance is extremely high. Mole concepts were introduced in order to represent atoms and molecules in a larger context. It takes 6.022 x 1023 atoms of any substance to make up one mole of that substance. Avogadro’s number is another name for this number. 

The molar mass of a substance is the gram weight per mole of the substance. Molar mass equals atomic/molecular formula mass for every mole of the substance. 

Let’s look at an example of a chemical equation that is in equilibrium. 

3Fe (s) + 4H2O (l) – Fe3O4 (s) + 4H2(g) 

This balanced chemical equation yields the following quantitative information: 3 moles of Fe react with 4 moles of H2O to produce 1 mole of Fe3O4 and 4 moles of H. 

H2O and Fe react to produce 231g of Fe3O4 and 8g of H2 gas, respectively, from 168g of Fe (563). 

It is important to consider the molar volume if the reactants and products are in gaseous form. The volume occupied by one mole of a gas is 22.4 litres. 

This reaction produces CO2 (g) and 2H2O (g) from CH4  and O2 (g)  

22.4 Litres of CH4 and 44.8 Litres of O2 react to produce 22.4 Litres of CO2 and 44.8 Litres of H2O in the above reaction.

Stoichiometry in Chemical Analysis

It is common practice for chemists to use stoichiometry calculations to estimate the concentrations of substances in a sample. For the most part, analysis is divided into two categories. We’ll cover them in detail below. 

• Analysis of Gravimetric Forces 

The gravimetric method is used in analytical chemistry to determine the amount of analyte in a sample based on its mass. It is the Gravimetric Analysis that provides the most accurate results out of all other analytical methods because the weight of a substance can be measured with great precision. 

This type of Gravimetric Analysis can be broken down into the following general categories: 

• An ion in solution is isolated by precipitation, the ion is filtered, the precipitate is washed of contaminants, and the precipitate mass is determined by difference. 
• By heating or chemically decomposing the sample, volatilization gravimetry separates the components of a mixture. 
• Using electrogravimetry, a metal ion is reduced at the cathode and deposited on the cathode simultaneously. To determine how many analytes were present in the sample prior to electrolysis, cathode weight is compared before and after electrolysis. 

•  Volumetric Analysis 

Substances are measured in volumetric units, and this is known as volumetric analysis. 

To calculate the concentration of an unknown substance (N2), one must first know the volume of the known substance (V1), which is then reacted with an unknown volume (V2) of the unknown solution. At the end of the reaction, the volume, V1, is recorded. Use the following formula to calculate N2 concentration. 

N1 x V1 = N2 x V2. 

A change in colour or precipitation, for example, signals the reaction’s completion. 

Volumetric analysis terminology; 

• To find out the volume of solution that must be added to another solution in order for it to completely react, titration is used. 
• The titrant is a solution that has a known strength. 
• The concentration of the titrated solution is being measured. 
• When the reaction is complete, the indicator limiting reagent changes colour.

The Calculations of the Mole and the Molar Mass

Many students give up at this point when they can’t figure out what a mole is. This surprises me. Having this in mind made things a lot easier for me: a mole is simply a count of how many. I’ll start with a dozen because it’s the most commonly used unit, and everyone knows what it is.

What if you have a dozen of them? What exactly does this mean? Having twelve of something means you have a lot of it. There’s no mention of how much weight it carries or how much space it takes up. The mass and volume of a dozen siege tanks and a dozen specks of dust are not the same. Only twelve of each are available. 

The concept of moles is the same. It takes 6.022 x 1023 objects to make up one mole of a given substance. Although it’s quite a lot, the atom is a good unit of measurement in chemistry. Avogadro’s number is 6.022 x 1023, also known as Avogadro’s number. It’s quite a large number, though. The age of the Earth is 4 million times longer than a single mole of seconds. It takes more than 600 times the Milky Way’s diameter to measure a mole of metres. It’s a good fit for our needs. 

Understanding the relationship between AMU and moles is critical. At the molecular level, 1 amu = 1 gram. To put it another way, the mass of one kilogram equals 6.022 x 1023 amus. To put it another way, 1.0079 x 2 = 2.0158 grams per mole of hydrogen (H2). That’s how they came up with Avogadro’s number: one mole of carbon weighs exactly 12 grams. 

Often, it is necessary to determine how many moles a given mass contains. To do this, you can employ dimensional analysis (DA). What if you want to know how many moles of water 36 grams contain as well as its total molecular weight? To begin, determine water’s molar mass (how many amus it weighs). H2O, or hydrogen and oxygen, is the formula for water. 

To put it another way, the mass sum of the two masses added together is: 

1.008 x 2 + 16.00 = 18.00 amu. 

The DA phase is now complete. 

So it’s two moles. As a result, there are 1.2 x 1024 molecules in a mole of NA molecules. 

Getting the g/mol (molar mass, or amus) of the substance is the key to solving these problems and then using that in a DA setup to convert grams to moles. One amu is equal to one g/mol of molecular weight.