How Much Butane is Needed for 33440J of Energy? Combustion Equation and Solution

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In summary, the equation given for the combustion of butane indicates that for every 2 moles of butane reacting with 13 moles of oxygen, 5760 kJ of heat energy will be released. To calculate the mass of butane needed to produce 33440 J of energy, first convert the energy to kJ and then use the molar ratio to calculate the number of moles of butane needed. The correct definition of enthalpy of combustion should be used to ensure accurate calculations.
  • #1
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Homework Statement


The combustion of the fuel gas butane is given by:

2(C4H10) +13(O2) --> 8(CO2) + 10(H2O) del(H)= –5760kJ/mol

What mass of butane would be needed to produce 33440J of energy?



Homework Equations





The Attempt at a Solution


First of all how do you interpret del(H)= –5760kJ/mol
Per mol of what?

I assume a mol is the complete reaction of
[2(C4H10) +13(O2) --> 8(CO2) + 10(H2O)]

33440J/(5760kJ/mol)=0.0058mol of the reaction

So a total of 0.0058*2=0.0116 moles of butane?

Which would be 0.012*(12.01*4 + 10.1)=0.675g of butane but the answers suggested 0.337g which is a half of what I worked out. Hence they didn’t multiply by 2. This confusion comes back to my first question. ‘Per mol of what?’ In del(H)= –5760kJ/mol
 
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  • #2
pivoxa15 said:

Homework Statement


The combustion of the fuel gas butane is given by:

2(C4H10) +13(O2) --> 8(CO2) + 10(H2O) del(H)= –5760kJ/mol

What mass of butane would be needed to produce 33440J of energy?

Homework Equations


The Attempt at a Solution


First of all how do you interpret del(H)= –5760kJ/mol
Per mol of what?

No. of moles is the stoichiometric coeff. in a balanced eqn.

oh BTW, how is the eqn represented in the text...i mean like
2(C4H10) +13(O2) --> 8(CO2) + 10(H2O) + 5760 J
or
is the energy evolved given separately like 5760 J/mol
In case 1, 2 mol give 5760 J while in case 2, 1 mol gives 5760 J
 
Last edited:
  • #3
pivoxa15 said:

Homework Statement


The combustion of the fuel gas butane is given by:

2(C4H10) +13(O2) --> 8(CO2) + 10(H2O) del(H)= –5760kJ/mol

What mass of butane would be needed to produce 33440J of energy?



Homework Equations





The Attempt at a Solution


First of all how do you interpret del(H)= –5760kJ/mol
Per mol of what?
If it is specified as [itex]\Delta H_c[/itex] (enthalpy of combustion), then it is per mole of the hydrocarbon being combusted. If it is specified as [itex]\Delta H_r[/itex] (enthalpy of reaction), then it would not come in units of kJ/mol, and would simply be in units of kJ. This would indicate the question is talking about an enthalpy of combustion, so it's for 1 mole of butane.
 
  • #4
That's strange, in another part of the book, it stated the equation
2(C2H6) + 7(O2) --> 4(CO2) + 6(H2O) del(H)=-2856kJ/mol

and explained, "This equation means that if 2 moles of C2H6 reacts with 7 moles of O2, then 2856 kJ of heat energy will be released." But the answers worked out didn't go by this convention.
 
  • #5
pivoxa15 said:
That's strange, in another part of the book, it stated the equation
2(C2H6) + 7(O2) --> 4(CO2) + 6(H2O) del(H)=-2856kJ/mol

and explained, "This equation means that if 2 moles of C2H6 reacts with 7 moles of O2, then 2856 kJ of heat energy will be released."
This is definitely WRONG. Which text is this?

But the answers worked out didn't go by this convention.
Did the given answers use the correct definition?
http://www.answers.com/topic/standard-enthalpy-change-of-combustion
 

1. What is the significance of "per mol" in scientific measurements?

Per mol, or per mole, is a unit of measurement commonly used in chemistry and physics to express the amount of a substance. It represents the number of particles, usually atoms or molecules, in a given sample of a substance. This unit is important because it allows scientists to quantify the amount of a substance in a consistent and precise manner.

2. Is "per mol" the same as "per molecule"?

No, "per mol" and "per molecule" are not the same. "Per mol" refers to the number of moles, while "per molecule" refers to the number of individual particles. One mole of a substance contains Avogadro's number of particles, which is approximately 6.022 x 10^23. Therefore, one mole of a substance contains a much larger number of particles than just one molecule.

3. Can "per mol" be used to measure any substance?

Yes, "per mol" can be used to measure any substance, as long as the number of particles in the substance can be determined. This unit is commonly used for elements, compounds, and even mixtures. However, it is important to note that the number of particles in a substance may vary depending on the type of substance and its molecular structure.

4. How is "per mol" different from other units of measurement?

"Per mol" is a unit of measurement used to express the amount of a substance, while other units such as grams or liters are used to express the mass or volume of a substance. "Per mol" is also a dimensionless unit, meaning it does not have a physical dimension like length or time.

5. Why is "per mol" often used in chemical equations?

"Per mol" is commonly used in chemical equations because it allows scientists to balance the equation by comparing the number of moles of each element or compound involved. This helps to accurately represent the reactants and products in a chemical reaction and determine the stoichiometry, or the relative amounts of substances involved.

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