4Fe + 3O2 -> 2Fe2O3 + 1.65E3 kJ
C) what is the enthalpy change for the formation of 23.6 g of iron(iii) oxide?
I'm trying to understand thermochemical reactions and stoichiometry, so could you please tell me if this is correct? And please explain the parts that I clearly don't understand:
The question, is it the same thing as asking, "how much energy was released if iron(iii) oxide had a mass of 23.6 g?"
According to the equation:
4 moles of Fe and 3 moles of O2 react to release -1.65E3 kJ. ....then 2 moles of Fe "contains" -1.65E3 kJ??
To calculate how much kJ of energy was released when the mass of Fe2O3 was 23.6g, we need the amount of moles:
23.6 g are in 1 mole of Fe2O3, and every mole of Fe2O3 is 160g, the molar mass. (??) which, I think??, explains why this works :
23.6g Fe2O3 x 1 mol Fe2O3/160g
And Since there's -1.65E3 kJ per 2 moles of Fe2O3: -1.65E3/2 mol Fe2O3
Putting it altogether:
Enthalpy = 23.6 g Fe2O3 x 1 mol Fe2O3/160g x -1.65E3kJ/2 mol 2Fe2O3
= 1.22E2 kJ
I'm hoping I've got the units all right too...
Also, what does it mean if "there's -1.65E3 kJ per 2 moles of Fe2O3"? Then there's -1.65E3 kJ 'contained' in the Fe2O3??? Because we wouldn't say -1.65E3 kJ is RELEASED when Fe2O3 reacts, because Fe2O3 is the product... So what exactly is going on (between Fe2O3 and the energy or enthalpy change or whatever.......)??
You are on the right track, and your understanding of stoichiometry and thermochemical reactions is mostly correct. Let's go through it step by step to ensure clarity.
First, let's address your question about the enthalpy change for the formation of iron(III) oxide. Yes, you are correct, it is asking about how much energy is released when iron(III) oxide has a mass of 23.6 g.
In the balanced equation you provided (4Fe + 3O2 -> 2Fe2O3 + 1.65E3 kJ), you can interpret the coefficients as mole ratios. So, for every 4 moles of Fe and 3 moles of O2, 2 moles of Fe2O3 are formed along with the release of 1.65E3 kJ.
To calculate the enthalpy change for the formation of iron(III) oxide with a mass of 23.6 g, you need to determine the number of moles of Fe2O3. You correctly used the molar mass of Fe2O3 (160 g/mol) to convert grams to moles:
23.6 g Fe2O3 x 1 mol Fe2O3/160 g Fe2O3
Now, since the balanced equation tells us that 2 moles of Fe2O3 are formed with the release of 1.65E3 kJ, we can use this ratio to find the enthalpy change:
(23.6 g Fe2O3 x 1 mol Fe2O3/160 g Fe2O3) x (-1.65E3 kJ/2 mol Fe2O3)
Simplifying this expression will give you the enthalpy change for the formation of 23.6 g of iron(III) oxide, which you correctly calculated as 1.22E2 kJ.
Regarding your question about "there's -1.65E3 kJ per 2 moles of Fe2O3," it means that during the reaction, for every 2 moles of Fe2O3 formed, 1.65E3 kJ of energy is released. The negative sign indicates that the reaction is exothermic, meaning it releases energy. It doesn't mean that the energy is "contained" in Fe2O3, but rather that the formation of Fe2O3 from Fe and O2 results in the release of that amount of energy per 2 moles of Fe2O3.
Your understanding of the problem is mostly correct. Let's break down the steps and address your questions one by one:
1. The question is indeed asking for the enthalpy change, or the amount of energy released or absorbed, for the formation of 23.6 g of iron(III) oxide (Fe2O3).
2. According to the balanced equation:
4 moles of Fe + 3 moles of O2 -> 2 moles of Fe2O3 + 1.65E3 kJ
This tells us that 2 moles of Fe2O3 releases 1.65E3 kJ of energy.
3. To determine the amount of energy released when the mass of Fe2O3 is 23.6 g, we need to find the number of moles of Fe2O3.
- The molar mass of Fe2O3 is indeed 160 g/mol, so 1 mol of Fe2O3 weighs 160 g.
- To find the number of moles of Fe2O3 in 23.6 g, you divide the mass by the molar mass:
23.6 g Fe2O3 x (1 mol Fe2O3/160 g Fe2O3) = 0.1475 mol Fe2O3
4. Finally, to calculate the enthalpy change, we use the ratio from the balanced equation, which tells us that 2 moles of Fe2O3 release 1.65E3 kJ of energy.
- So, in 0.1475 mol Fe2O3, the enthalpy change can be calculated as follows:
0.1475 mol Fe2O3 x (-1.65E3 kJ/2 mol Fe2O3) = -122.5 kJ
The negative sign indicates that the reaction is exothermic, meaning it releases energy.
Regarding your question about "there's -1.65E3 kJ per 2 moles of Fe2O3," it means that for every 2 moles of Fe2O3 produced, 1.65E3 kJ of energy is released. This ratio is taken from the balanced equation. So, in this reaction, Fe2O3 acts as a product and releases energy.
Your units are correct, and your overall understanding of the calculation is accurate.