Enthaply Calculations

There's nothing do with Enthalpy Calculation in this picture... just my feeling under the test.. 

As we knew that, there'll have either absorbing or releasing energy during the reaction, like the equation from below~
CH4+ 2O2 > CO2 + 2H2O + 812kJ 
And now, we can turn it into mole by "ENTHALPY CALCULATION"

The unit of enthalpy calculation will be KJ/mol,  which has shown that  "KJ divided by mol"

As the equation from above, we can tell  "4" different equation from it, as there have 4 different substance in either reactant or product side.

- 812KJ/1 mole of CH4      -812KJ/2 mole of O2      -812KJ/1 mole of CO2      -812KJ/2mole of H2O
The moles of the compouds are determinded by the number of them individualy in the equation
Moreover,  as it's "releasing", which causes a "NEGATIVE" number

I am BACK~

So, Ex 1) How many moles of CH4 are needed to produce 3000KJ?

First, we can write  -3000KJ DOWN,  and multiply the "CH4" equation from below, which is -812KJ/1CH4

-3000KJ x  1CH4 / - 812KJ   (As we want to reduce the KJ, so that we can get the mole)

3.49458128.......  moles of CH4
SIGFIG TIME~~~
There is only 1 sigfig in - 3000,  so     the answer 'll be  "4 mol of CH4"

Moreover, BE CAREFUL THE QUESTION, ESPECIALLY IT MIGHT ASKS FOR "GRAMS"
As we know one more method to turn it into mole, there possibly will have "Mole Converstion" back

Anyway, GOOD LUCK....