STOICHIOMETRY

What is stoichiometry?Stoichiometry is the quantitative study of reactants and products in a chemical reaction.

What You Should ExpectGiven : Amount of reactants Question: how much of products can be formed. Example 2 A + 2B 3CGiven 20.0 grams of A and sufficient B, how many grams of C can be produced?

What do you need?You will need to use molar ratios, molar masses, balancing and interpreting equations, and conversions between grams and moles.

Note: This type of problem is often called "mass-mass."

Steps Involved in Solving Mass-Mass Stoichiometry ProblemsBalance the chemical equation correctlyUsing the molar mass of the given substance, convert the mass given to moles. Construct a molar proportion (two molar ratios set equal to each other) Using the molar mass of the unknown substance, convert the moles just calculated to mass.

Mole Ratios A mole ratio converts moles of one compound in a balanced chemical equation into moles of another compound.

ExampleReaction between magnesium and oxygen to form magnesium oxide. ( fireworks)

2 Mg(s) + O2(g) 2 MgO(s) Mole Ratios:2 : 1: 2

1) N2 + 3 H2 ---> 2 NH3 Write the mole ratios for N2 to H2 and NH3 to H2. 2) A can of butane lighter fluid contains 1.20 moles of butane (C4H10). Calculate the number of moles of carbon dioxide given off when this butane is burned.Practice Problems

Mole-Mole Problems Using the practice question 2) above: Equation of reaction 2C4H10 + 13O2 8CO2 + 10H2O Mole ratioC4H10 CO2 1: 4 [ bases] 1.2 : X [ problem] By cross-multiplication, X = 4.8 mols of CO2 given off

Mole-Mass ProblemsProblem 1: 1.50 mol of KClO3 decomposes. How many grams of O2 will be produced? [k = 39, Cl = 35.5, O = 16]

2 KClO3 2 KCl + 3 O2

Three stepsGet Your Correct AnswerUse mole ratioGet the answer in moles and thenConvert to Mass. [Simple Arithmetic]

Hello!If you are given a mass in the problem, you will need to convert this to moles first. Ok?

Lets go!2 KClO3 2 KCl + 3 O22: 31.50 : XX = 2.25molConvert to mass2.25 mol x 32.0 g/mol = 72.0 gramsCool!

Try This:We want to produce 2.75 mol of KCl. How many grams of KClO3 would be required?

SolnKClO3 :KCl2 : 2X :2.75X = 2.75molIn mass: 2.75mol X 122.55 g/mol = 337 grams zooo zimple!

Mass-Mass ProblemsThere are four steps involved in solving these problems:Make sure you are working with a properly balanced equation. Convert grams of the substance given in the problem to moles. Construct two ratios - one from the problem and one from the equation and set them equal. Solve for "x," which is usually found in the ratio from the problem. Convert moles of the substance just solved for into grams.

Just follow mass-mass problem to the penultimate levelMass-Volume Problems

Like this:There are four steps involved in solving these problems:Make sure you are working with a properly balanced equation. Convert grams of the substance given in the problem to moles. Construct two ratios - one from the problem and one from the equation and set them equal. Solve for "x," which is usually found in the ratio from the problem. Convert moles of the substance just solved for into Volume.

Conversion of mole to volume

No of moles = VolumeMolar volumeCan you remember a similar equation?

Molar volumeThe molar volume is the volume occupied by one mole of ideal gas at STP. Its value is: 22.4dm3

Practice ProblemsCalculate the volume of carbon dioxide formed at STP in dm3' by the complete thermal decomposition of 3.125 g of pure calcium carbonate (Relative atomic mass of Ca=40, C=12, O=16)Solution: Convert the mass to mole:Molar mass of CaCO3 = 40 + 12 + (16 x 3) = 100gmol-1Mole = mass/molar mass3.125/100 = 0.03125mol

Practice ProblemsAs per the equation,Mole ratio1 : 1problem0.03125mol XX = 0.03125mol of CO2Convert mole to volume [slide 17]Volume = (0.03125 x 22.4)dm3 = 0.7dm3

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