Question

Consider this combination reaction:
2Mg(s)+O2(g)→2MgO(s) ΔH=−1204 kJ
What is the enthalpy for the decomposition of 1 mole of MgO(s) into Mg(s) and O2(g)?
Consider this combination reaction:
What is the enthalpy for the decomposition of 1 mole of into and ?
-1204 kJ/mol
602 kJ/mol
1204 kJ/mol
-602 kJ/mol

Answer 1

it's (a) right? This is a trick question or am I just too dumb to see this? @Photon336

Answer 2

@Kainui

Answer 3

I'm confused what the question is, it looks like there are two here and the second one got cut off

Answer 4

well A isn't the answer lol I am confused too

Answer 5

hold on....

Answer 6

Consider this combination reaction:
2Mg(s)+O2(g)→2MgO(s) ΔH=−1204 kJ
What is the enthalpy for the decomposition of 1 mole of MgO(s) into Mg(s) and O2(g)?

Answer 7

Sorry did a copy and paste, apparently it didn't copy everything

Answer 8

Well it looks like you're asking for what's the reverse reaction of a single mole of MgO. So you'll have to change two things.

Right now you lose 1204 kJ of heat to go from left to right. But you now want to go from right to left, so you need to gain 1204 kJ of heat to reverse it. So \(\Delta H = +1204 kJ\) for the reverse... However this isn't all, cause that reaction is for 2 moles of MgO. So now you just divide it by 2. Done!

Answer 9

Why do we divide by 2?

Answer 10

The ratio is 1:1

Answer 11

2:2

Answer 12

Ahhh good question, it's because it takes half as much heat for half as much molecules.

The difference is between what you're given here:
2Mg(s)+O2(g)→2MgO(s) ΔH=−1204 kJ

and what your reaction is concerned with is a single mole of MgO:
Mg(s)+(1/2)O2(g)→MgO(s) ΔH=−602 kJ

Everything is reduced by a half

Answer 13

Well wait, you didn't really say anything specific, just Enthalpy not Molar Enthalpy right?

Answer 14

Yeah, but I see what you are doing there. You are using least common multiple.

Answer 15

mathematically I understand but conceptual having a bit of ahard time seeing it.

Answer 16

This heat we are looking at is the amount of heat causing the chemical reaction? It takes 602kJ to break the bonds?

Answer 17

Really what I'm saying is 2MgO takes 1204 kJ of heat to decompose so if you have half as much, so that means 1MgO then it must take half as much heat to decompose, 602 kJ.

Imagine you have two pots of water and one has twice as much water than the other, then it takes twice as much heat to get it to boil. Same kinda idea.

Answer 18

Oh okay lol thanks that makes more sense!

Answer 19

Cool :P