Topscore Test 2 GC #10

[Meat Gyver]

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Using the bond energies, estimate the standard heat of combustion per mole of hydrogen gas when combined with oxygen.

Bond (with corresponding bond energy)
H-H 436 kJ/mol
O=O 498 kJ/mol
H-O 464 kJ/mol

My answer: (((2*436)+498) - (4*464))

Their answer: (((2*436)+498) - (4*464))/2 <why would you divide the whole answer by 2?

To add, in the explanation they say that the value should come out to -486kJ (which is what my answer comes out to).

So is their explanation wrong, or did they make a mistake with the correct letter of the answer?

Also, has this happened to anyone else:

Finished PAT early

Clicked NEXT to the 15 minute break window
-However the time for PAT was still on

Ran to my kitchen real quick

Came back just as the timer for PAT was ending (even though I finished that section)

Some notification comes up saying that my time is up (okay cool...onto RC)

....GOES RIGHT TO QR, AND COMPLETELY SKIPPED RC (the main reason why I took the test in the first place)!

and I'm 100% sure I didn't spend 60 minutes in my kitchen.

Not fun, especially when your RC score comes out to a 1 (0.00%).

 

[yeagerbomb]

I'm guessing that the reason they divide by two is because in the balanced equation there are two moles of hydogen gas and the question specifies finding the heat of combustion per ONE mole of hydorgen gas. Don't hold me to it but I would bet the correct answer is -243kJ. I too have come across a few of these issues.

When are you taking the DAT just out of curiosity?

 

[Meat Gyver]

I'm guessing that the reason they divide by two is because in the balanced equation there are two moles of hydogen gas and the question specifies finding the heat of combustion per ONE mole of hydorgen gas. Don't hold me to it but I would bet the correct answer is -243kJ. I too have come across a few of these issues.

When are you taking the DAT just out of curiosity?

Ahh definitely overlooked that part. You're 100% right. Thanks for the clarification (way better than any Topscore explanation)!

My DAT is in 5 days though.

 

[yeagerbomb]

Nice, mine is on Thursday. You havent happened to find any extra pattern folding practice stuff have you?