Well anytime you're given a thermal chemical equation,

you're giving a relationship between the enthalpy change and

the number of moles of that substance in the balanced equation.

What we can do is set up a, conversion factor for any substance in there.

That is related to the value of the delta H.

So this many kilojoules, would be produced in terms of the substance

we're interested in, when 2 mols of O2 react.

Like I said we can do this for

any sets that you can put down here in the denominator 1 mol of methane.

We could put in the denominator 1 mol of carbon dioxide.

We can put into the denominator 2 mols of water.

Since this question is acting for relationship, of heat for

the oxygen, we're going to use this first one that I wrote.

Don't start with that, start with what's given then we have 2.5 mols of oxygen.

And then do your typical dimensional analysis, I don't want moles of oxygen.

I want kilojoules of heat.

And there are a negative 890.4 kilojoules for every 2 mols of oxygen that react.

That gives to us a value of negative

1,113 kilojoules or.

To two significant figures.

That would be 1.1 times 10 to the 4th kilojoules.

Now this is a little bit more, than what 2 mols would provide.

And you'd expect that.

2 mols gives off,

as you have a minus sign there and there, gives off 890.4 kilojoules.

This is more.

So, I would expect more heat.

And indeed, it is more heat.