## Chemistry Tutorial

#### Intro

EASY STOICHIOMETRY CHEMISTRY

What is Stoichiometry?

Stoichiometry involves calculations with understanding of basic concepts of chemical equations. It is a mathematical part of balanced chemical equations and reactant-product mole ratio.

If mass of one of the reactants or products in a chemical reaction is given, mass of another reactant or product can be calculated using the mole ratio of a chemical equation.

Example

Consider a reaction

H2(g)+O2(g) →H2O(l) ( Unbalanced or Skeleton equation)

2H2(g)+O2(g) →2H2O(l) (Balanced equation)

2 mole of H2 : 1 mole of O2 : 2 mole of H2O

Mole ratio is 2:1:2

By this similar method, mass of oxygen can be calculated.

Mass of the given reactant given in problem → conversion of mass of the reactant into moles of the reactant using molar mass of the reactant → use of molar ratio of reactant to product → conversion of moles of the reactant into moles of the product → calculation of mass of the produt by multiplying with molar mass of product.

Practice Problems

1.What is the mass of Oxygen needed to produce 90 g of water?

( Verify: 80 g of Oxygen)

2.What is the mass of Hydrogen needed to produce 90g of water?

( Verify: 10 g of Hydeogen)

REFERENCES

1. Zumdahl: Chemistry (6th edition) will be fine.

2. www.chemteam.info/Stoichiometry/Stoichiometry.html

3.http://chemwiki.ucdavis.edu/Analytical_Chemistry/Chemical_Reactions/Stoichiometry_and_Balancing_Reactions

4. To find symbols, atomic masses, etc.

www.ptable.com

www.amazon.com

#### Sample Problem

How many grams of H2O will be formed from 10 grams of H2?

#### Solution

Solution

Consider a reaction

H2(g)+O2(g) →H2O(l) ( Unbalanced or Skeleton equation)

2H2(g)+O2(g) →2H2O(l) (Balanced equation)

2 mole of H2 : 1 mole of O2 : 2 mole of H2O

Mole ratio is 2:1:2
10 g of hydrogen = 10 g of hydrogen/(2 g /mole of hydrogen) = 5 moles of hydrogen

Number of moles of water = 5 moles of hydrogen x 2 moles of water/2moles of hydrogen =5 moles of water

Mass of water = 5 moles of water x 18 g water/mole of water = 90 g water ( Molar mass of water= 18 g/mole)
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