Hess's law rule?

[joonkimdds]

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do we not care about balancing O and H2O but everything else?

 

[GCT]

Please be more specific , why would you not balance the oxygen and water ?

 

[joonkimdds]

Ok here is an example.
Given: 2C(s) + 2H2(g) + H2O(l) ==> C2H5OH(l)

a) H2O(g) ==> H2O(l) delta H = -44
b) C(s) + O2(g) ==> CO2(g) delta H = -394
c) H2(g) + 1/2O2(g) ==> H2O(l) delta H = -286
d) C2H5OH(l) +3O2(g) ==> 2CO2(g) + 3H2O(l) delta H = -1367
how would u solve this?



another question is
Given: Rh(s) + O2(g) ==> RhO2(s)
a) 2Rh(s) + O2(g) ==> 2RhO(s) delta H = -800kJ
b) 2RhO (s) + O2 (g) ==> 2RhO2(s) delta H = -300kJ


after solving these two problems, all i can say is that we don't care about balancing or existance of O2 and H2O.

Edit: I got another example but same thing applies, no O2 and H2O count.
so unless this argument goes really seriously long, I won't post it but I still can 🙂

 

[GCT]

The equations are already balanced you simnply need to cancel out the agents that are not in the original equation by rearranging them oxygen and water count just as well as those other compounds .

 

[joonkimdds]

For the first problem, we completely ignore
a)H2O(g) => H2O(l) so delta H=-44 will not even be included to the calculation.
also, if you look at c), it has H2O on the right side but it is supposed to be on the left side.

For the 2nd problem, take a look at a).
Rh is doubled but O2 is same as the given equation.
If we divide it by 2 to make 2Rh into 1Rh just like the given formula, that will cause O2 into 1/2O which is different from the given formula.

Because of these reasons, I think we don't care about oxygen and water.

 

[GCT]

For the first problem, we completely ignore
a)H2O(g) => H2O(l) so delta H=-44 will not even be included to the calculation.
also, if you look at c), it has H2O on the right side but it is supposed to be on the left side.

For the 2nd problem, take a look at a).
Rh is doubled but O2 is same as the given equation.
If we divide it by 2 to make 2Rh into 1Rh just like the given formula, that will cause O2 into 1/2O which is different from the given formula.

Because of these reasons, I think we don’t care about oxygen and water.

You are right about the first question part a) is not needed however the problem itself is fine the water is in place the whole equation needs to be multiplied by two and if d) is reversed then you have the one water on the left by cancellation which is what you need to produce the original equation .

 

[GCT]

You make the same wrong assumption on the second question the coefficient is 2 dividing by 2 is going to give you 1 .

 

[joonkimdds]

You are right about the first question part a) is not needed however the problem itself is fine the water is in place the whole equation needs to be multiplied by two and if d) is reversed then you have the one water on the left by cancellation which is what you need to produce the original equation .

wait, so how am I supposed to know that I am ignoring a) on the 1st problem?