This isn't exactly a homework question, I'm just trying to understand the concept we learned today...
So say we had:
4Fe + 3O2 → 2Fe2O3 + 1.65 x 10^3 kJ
Does that mean for every 4 mol of Fe, 3 mol of O2, and 2 mol of Fe2O3 we have 1.65 x 10^3 kJ?
And if I were to calculate what the enthalpy change for the formation of 23.6 g of iron(iii) oxide was,
Would it be 23.6g Fe2O3 or 23.6g of 2Fe2O3 that I would use in the equation...? When do you account for the fact that there's 2 moles of Fe2O3?
My confused attempt at solving:
Enthalpy=23.6g Fe2O3 x 1 mol Fe2O3/[(2x56) + (3x16)]g x -1.65x10^3 kJ/1 mol Fe2O3
= -243.38 kJ
Yeah, I'm pretty confused; can someone please clear things up for me??
Also, I guess it's not that important but how come when doing 1mol of Fe2O3/molar mass of Fe2O3 you can just do 1mol/160g instead of 1mol/160g/mol?? Because for molar mass we always use the unit g/mol...
Thanks so much in advance !! It's only the second lesson in grade 12 chemistry and I'm already lost! Not good.. :(
yes, for each reaction in the balance equation, you get that energy.
Now for 23.6g FeOxide, you do not have two moles, you have to figure what part of the energy you get.
Enthalpy= 23.6g Fe2O3/(160g) * 1.65E3Kj/2molesFe2O3
examine the last term, it is different from yours. Why? Look at the balanced equation
Okay so after some trial and error (I just kept trying different things Until I got the answer), I figured out it's *probably* solved like this:
Enthalpy = 23.6g Fe2O3 x 1 mol Fe2O3/[(2x56) + (3x16)]g x -1.65x10^3 kJ/2 mol Fe2O3
= -1.22 x 10^2 kJ
If that's right, my question is, how come you divide -1.65 x 10^3 kJ by *2* mol Fe2O3 but you don't use that when you do the other calculation (I know I'm being vague - sorry; I just don't even know what the "other calculation" is even doing/calculating so I can be more specific...): *1* mol Fe2O3/[(2x56) + (3x16)]g
Here, you don't account for the fact that there's 2 mol of Fe2O3 in the equation? Why?
Basically... What's going on???
Sorry, I posted the above before I got to see your answer, bobpursley. I think I get it a little more but could you clarify a bit more based on what I asked above?
Thanks for answering!!
"Now for 23.6g FeOxide, you do not have two moles, you have to figure what part of the energy you get."
Could you clarify what you mean by that? I think this is closer to answering and fixing my confusion; what do you mean by "what part of the energy you get"?
You got 1.65E3Kj for each two moles of product. You did not have two moles, you had 23.6 grams, and the point of the conversion was to figure out what part of two moles you had, then multply that by 1.65E3 Kj
I'm really sorry, but I still don't really understand - what do you mean by "figure out what part of two moles you had "?
well i think it will be 183g
what type of reaction is Mg+2HCl-->MgCl2+H2
I can help clarify your questions and provide some guidance for your understanding.
To answer your first question, yes, the balanced equation you provided indicates that for every 4 moles of Fe, 3 moles of O2, and 2 moles of Fe2O3 formed, the reaction releases 1.65 x 10^3 kJ of energy.
Now let's move on to your question regarding the enthalpy change for the formation of 23.6 g of iron(III) oxide (Fe2O3). To determine the enthalpy change, we need to use the given equation and mole ratios.
First, we need to calculate the number of moles of Fe2O3 present in 23.6 g. To do this, divide the mass of Fe2O3 (23.6 g) by its molar mass. The molar mass of Fe2O3 is calculated by adding the atomic masses of the elements: (2 x atomic mass of Fe) + (3 x atomic mass of O). The atomic masses can be found on the periodic table.
Next, use the mole ratio from the balanced equation to determine the moles of Fe consumed or produced in the reaction. From the balanced equation, we see that 2 moles of Fe2O3 are formed for every 4 moles of Fe. Therefore, divide the number of moles of Fe2O3 by 2 to find the moles of Fe.
Once you have the moles of Fe, use the mole ratio again to determine the number of moles of O2 involved in the reaction. From the balanced equation, we see that 3 moles of O2 are needed for every 4 moles of Fe. Therefore, divide the number of moles of Fe by 4 and multiply by 3 to find the moles of O2.
Now that you have the moles of Fe, O2, and Fe2O3, you can calculate the enthalpy change using the balanced equation's ratio of moles and the given energy change. Multiply the moles of Fe2O3 by the energy change per mole (1.65 x 10^3 kJ) to find the enthalpy change in kJ.
Regarding your confusion about the unit for molar mass, the unit g/mol is indeed used when expressing the molar mass of a substance. In the calculation you provided, 1 mol/160 g is the reciprocal of the molar mass. It represents the conversion factor to convert between moles and grams. Multiplying this conversion factor by the given mass (23.6 g) of Fe2O3 gives you the number of moles of Fe2O3.
I hope this explanation clears up your confusion. Feel free to ask any further questions!