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

Click For Summary

Discussion Overview

The discussion revolves around a homework problem involving the combustion of potassium (K) and the calculation of the internal energy of formation for potassium oxide (K2O). Participants are examining the stoichiometry of the reaction and the calculations involved in determining the number of moles of K and K2O produced.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Conceptual clarification

Main Points Raised

  • One participant expresses confusion about why the number of moles of K is divided by 2 in the calculation, indicating a misunderstanding of the stoichiometry of the reaction.
  • Another participant asks how many moles of K2O are produced per mole of K, suggesting a need for clarification on the reaction's stoichiometry.
  • A subsequent reply confirms that 2 moles of K produce 1 mole of K2O, indicating a realization of the stoichiometric relationship.
  • Another participant counters this by stating "Quite the opposite!" without further elaboration, suggesting a disagreement or confusion regarding the stoichiometric interpretation.

Areas of Agreement / Disagreement

The discussion reflects some confusion and disagreement regarding the stoichiometry of the combustion reaction, particularly the relationship between moles of K and K2O produced. No consensus is reached on the correct interpretation of the stoichiometric coefficients.

Contextual Notes

Participants have not fully resolved the assumptions regarding the stoichiometric coefficients in the reaction, and there is ambiguity in the understanding of how the combustion calculation should be approached.

Samuel1321
Messages
11
Reaction score
0

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?
 
Physics news on Phys.org
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!
 

Similar threads

Replies
5
Views
4K
Replies
9
Views
3K
  • · Replies 4 ·
Replies
4
Views
3K
  • · Replies 2 ·
Replies
2
Views
3K
  • · Replies 1 ·
Replies
1
Views
2K
Replies
1
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 7 ·
Replies
7
Views
3K
  • · Replies 1 ·
Replies
1
Views
4K