Lecture 4 combustion and redox PDF

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combustion and redox notes...

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LECTURE 4 Balancing equations: Two types of reactions - Combustion - Redox Combustion: - Combustion is a reaction of a compounds (usually a hydrocarbon) and oxygen (O2) - We see combustion everyday with the reaction between methane (CH4) and oxygen - Combustion reactions will gve off an oxide and water as products (so id the compound contains carbon, it will give off CO2 and water) - General equation for combustion Hydrocarbon + O2 → CO2 + H2O 1. Write the reactants and products

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A combustion of an unknown compound resulted in 3.67g of CO2 produced and 1.50g of H2O. Calculate the empirical formula Using mass of CO2 produced, we can calculate the moles

mass = molar mass 3.67 = 0.0833 moles of CO2 12.01 +(2 x 16.0 )

Moles =

2. Balance everything but oxygen and hydrogen

Combustions can also tell us the empirical formula of the compound Based on the amount of CO2 and H2O produced, we can determine the empirical formula We use similar processes to compound analysis

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Moles of CO2 = moles of carbon in compound Carbon = 0.0833 moles Doing the same for water/hydrogen

Moles = 3. Balance hydrogen atom (rebalance the carbon if needed)

of H2O -

4. Balance Oxygen (multiply each coefficient by 2 if an odd number of oxygen are present

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Overall balanced equation

(1.01 x 2)+16.0 = 0.0832 moles 1.50 ¿ ¿

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1 moles of water formed 2 moles of hydrogen Moles ratio between H2O and H is 1:2 Therefore the moles of hydrogen from the unknown compounds is 2 x 0.0832 = 0.16867 Moles of C = 0.0833 → smallest number of moles Moles of H = 0.16867 Dividing by the smallest number of moles we will get an empirical

LECTURE 4 formula of CH2 Redox - Electrochemical or redox reaction involve the transfer of electrons between reactants - Redox reactions are used in: - Batteries - Metal refining - Metabolism of haemoglobin - Glow sticks - Very common, corrosion of metal - Some elements are easy and others hard to oxidise - The resistance of metals to oxidation is referred to as the activity

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Transfer of electrons occurs through two reactions that occur simultaneously

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Reduction - electrons gained Oxidation - electrons lost They are complementary and can’t occur without each other...