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DIMENSIONAL ANALYSIS CHEMISTRY SUPER easy MOLE CONVERSIONS!!

Question : How many moles of O2 are in the sample of 3.6 kilograms of air if 21% of the air is oxygen O2 by mass?

47.25 moles

Explanation:

First we find the amount of O2 in mass in air

That will be = (21/100) x 3.6

This will give us=0.756 kg

Now we want to find the moles, so we convert this mass into grams since we are going to be working with grams= 0.756 x 1000 = 756 grams

Now, to find the number of moles:

moles= mass / molar mass

in this case mass is 756 grams and molar mass of oxygen is 16

So, the mass divided by molar mass would be =756/16= 47.25 moles of O2

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the enthalpy of formation of water is given as -285.8kj/mol, which states that the enthalpy of formation is negative.

negative enthalpy of formation indicates that the heat is released during the reaction process. the heat is released from reaction to the surroundings the enthalpy is expressed with a negative sign with the energy given out in the reaction process.

the formation of water takes place by giving out heat which is -285.8 kj/mol.