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

In this conversation, the participants are discussing the calculation of the internal energy of formation for K2O. They are using the calorimeter constant and temperature rise to determine the change in internal energy during the combustion reaction. The key step in the calculation is dividing the number of moles of K by 2, which is necessary because the reaction produces 2 moles of K2O for every mole of K. In summary, the conversation involves calculating the internal energy of formation for K2O using a constant volume calorimeter, and the key step is dividing the number of moles of K by 2 due to the stoichiometry of the reaction.
  • #1
Samuel1321
11
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?
 
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  • #2
How many moles of K2O produced per each mole of K?
 
  • #3
Borek said:
How many moles of K2O produced per each mole of K?

2, I think I get it now, thanks!
 
  • #4
Samuel1321 said:
2

Quite the opposite!
 

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

1. What is a mole ratio in thermodynamics?

A mole ratio in thermodynamics is a ratio that compares the number of moles of one substance to the number of moles of another substance in a chemical reaction. It is used to determine the relative amounts of reactants and products in a reaction.

2. How is a mole ratio calculated?

A mole ratio is calculated by dividing the number of moles of one substance by the number of moles of another substance in a chemical reaction. This can be determined by using the coefficients in the balanced chemical equation.

3. Why is a mole ratio important in thermodynamics?

A mole ratio is important in thermodynamics because it allows us to predict the amounts of reactants and products in a chemical reaction. It also helps us understand the stoichiometry of a reaction and determine the limiting reactant.

4. How is a mole ratio used in determining enthalpy changes?

A mole ratio is used in determining enthalpy changes by allowing us to calculate the amount of heat released or absorbed in a reaction based on the number of moles of reactants and products. This information is then used in the calculation of enthalpy changes using the equation q = mCΔT.

5. Is a mole ratio affected by changes in temperature or pressure?

No, a mole ratio is not affected by changes in temperature or pressure. It is a fixed ratio based on the coefficients in a chemical equation and remains constant regardless of changes in conditions.

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