Chemistry Why Divide the Moles of K by 2 in Combustion Calculation?

AI Thread Summary
In combustion calculations for potassium (K), the number of moles of K is divided by 2 because the balanced reaction shows that two moles of K produce one mole of K2O. This stoichiometric relationship is crucial for accurately calculating the internal energy of formation for K2O. The calorimetry equation incorporates the heat absorbed by water and the calorimeter, and the factor of 2 ensures the correct amount of K2O is accounted for in the energy calculations. Understanding this stoichiometry is essential for solving combustion problems accurately. Accurate mole ratios are vital for precise thermodynamic calculations in chemistry.
Samuel1321
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Homework Statement


A sample of K (s) of mass 2.740g undergoes combustion in a constant volume calorimeter at 298.15K . The calorimeter constant is 1849 J/K , and the measured temperature rise in the inner water bath containing 1450 of water is 1.60K
Calculate the internal energy of formation for K2O

Homework Equations


DeltaU combustion = -(M/m)(m(H2O)/M(H2O)C(H2O)deltaT + Ccal delta T)

The Attempt at a Solution



2K+1/2O2 --> K2O

I basically just plugged everything inside but I was off by a factor of 2. When I look at the the answer key, they divided the number of moles of K by 2, I'm not quite sure why do we need to divide the number of moles of K by 2?
 
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How many moles of K2O produced per each mole of K?
 
Borek said:
How many moles of K2O produced per each mole of K?

2, I think I get it now, thanks!
 
Samuel1321 said:
2

Quite the opposite!
 
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