If heat of reaction, Ca(s) + 2H+(aq) Ca2+(aq) + H2(g) , is - 544 kJ/mol, heat of reaction, CaO(s) + 2H+(aq) Ca2+(aq) + H2O(l) , is -192 kJ/mol. and heat of formation of water is -286, what is heat of CaO?
i found that the formation of CaO is -638. However, I'm confused about the next step to find delta H for the end equation.
You're finished. That IS delta H for the end reaction which is the delta H formation for CaO.
Eqn1 is Ca(s)+2H+ ==> Ca^+2 +H2(g)
eqn2 reversed is
H2O + Ca+2 ==> 2H+ + CaO
eqn 3 is H2 + 1/2 O2 ==> H2O
I omitted most of the (aq) (g) and (s) to save time.
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Note 2H+ on left in eqn 1 cancels with 2H+ in eqn 2 on right.
H2 in eqn 2 on right cancels with H2 on left in eqn 3.
H2O on left in eqn 2 cancels with H2O
on right in eqn 3.
Ca(II) ion on right in eqn 1 cancels with Ca(II) ion on left in equn 2. All of that leaves.
Ca(s) + 1/2 O2(g) ==> CaO(s) delta H = -638 kJ/mol
If all of that confuses you, and it's easy to get confused with so many different ions and solids, just add th three equations I wrote. I have already reversed eqn 2. Then note that there are some ions and gases that appear on both sides and in the same quantity. Those can be canceled leaving the final equation I have above. I find it easier, however, to look on the left side somewhere in the equations I have, then find one like it on the right side and cancel it. Then I look for the next one etc until I have canceled everything I can. Then I write what is left. Works every time although it gets a little confusing if one of the equations must be multiplied by some constant. Fortunately, that step wasn't necessary in this problem.
Well, it seems like you've already done a great job in finding the heat of formation for CaO, which is -638 kJ/mol. That is indeed the delta H for the end reaction. So you're finished! Bravo! Now you can sit back, relax, and enjoy the heat of CaO without any further calculations.
You're correct! The heat of formation of CaO is -638 kJ/mol. This means that when 1 mol of CaO is formed from its constituent elements (Ca and O2), -638 kJ of heat is released. Therefore, the heat of reaction for the formation of CaO can be considered as the heat of formation for CaO.
The next step is to use the given heat of reaction for the formation of water, which is -286 kJ/mol. We can consider this as the heat released when 1 mol of water is formed from its constituent elements (H2 and 1/2 O2).
Now, we can write the desired reaction as the sum of the two reactions:
Ca(s) + 1/2 O2(g) + H2(g) → CaO(s) + H2O(l)
To find the heat of this reaction (ΔH), we need to combine the heats of the individual reactions. However, we need to make sure that the reactions are balanced in terms of the stoichiometric coefficients.
The given reaction for the formation of CaO is already balanced. For the formation of water, we can multiply the reaction by 2 to balance the number of moles of H2.
2(H2(g) + 1/2 O2(g) → H2O(l))
Now we can add the two reactions together:
Ca(s) + 1/2 O2(g) + H2(g) + 2(H2(g) + 1/2 O2(g)) → CaO(s) + H2O(l)
Simplifying this equation gives:
Ca(s) + 2H2(g) + O2(g) → CaO(s) + 2H2O(l)
Now we can find the heat of this reaction (ΔH) by adding the heats of the individual reactions:
ΔH = heat of formation of CaO + heat of formation of water
ΔH = -638 kJ/mol + (-286 kJ/mol)
ΔH = -638 kJ/mol - 286 kJ/mol
ΔH = -924 kJ/mol
Therefore, the heat of CaO is -924 kJ/mol.
To find the heat of formation of CaO, you need to use the given reactions and the concept of Hess's law. Hess's law states that the heat of a reaction depends only on the initial and final states, and not on the path taken to get from one to the other.
So, here's how you can find the heat of formation of CaO:
1. Start with the given equations:
- Eqn1: Ca(s) + 2H+(aq) -> Ca2+(aq) + H2(g)
- Eqn2 (reversed): H2O(l) + Ca2+(aq) -> 2H+(aq) + CaO(s)
- Eqn3: H2(g) + 1/2 O2(g) -> H2O(l)
2. Recognize that some species appear on both sides of the equations in the same quantity. These species can be canceled out:
- Cancel out 2H+(aq) and 2H+(aq) from Eqn1 and Eqn2.
- Cancel out H2(g) and H2(g) from Eqn1 and Eqn3.
- Cancel out H2O(l) and H2O(l) from Eqn2 and Eqn3.
This leaves us with the following simplified equation:
- Ca(s) + 1/2 O2(g) -> CaO(s)
3. The simplified equation represents the formation of CaO from its constituent elements. The heat associated with this reaction represents the heat of formation of CaO. Therefore, the heat of formation of CaO is equal to the delta H value obtained from the simplified equation, which is -638 kJ/mol.
So, the heat of formation of CaO is -638 kJ/mol.