Can someone please explain? GC

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When 1.00 g of liquid water (M.W. = 18) is produced from H2 and O2 at a constant temperature (25 dC) and pressure (1 atm), 15.8 kilojoules are produced. What is the molar heat of formation of liquid water, in kilojoules? 😡

(a) -15.8 x 18

(b) 15.8 x 18

(c) 15.8/18

(d) -15.8/18

(e) -18/15.8

 

[herkulease]

Mols X molar heat of formation = 15.8 kJ

1/18 X molar heat of formation = 15.8 kJ

molar heat of formation = 15.8kJ/(1/18 mols) or 15.8kJ X 18

 

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How did you know to use this formula?

 

[Aliengod3]

Molecules are being combined to create are larger molecule so the reaction is endothermic to Delta H is positive.

As for the answer it is just a conversion. There are 15.8 kJ/mol, 1g of water, and 18g/mol of water

 

[herkulease]

well you should know that molar heat of formation determined at 25C 1 atm. so that info that was given is just there to try to confuse those who don't remember that and think its part of solving the problem.

after that its just taking what is given to you and working backwards.

you don't necessarily need to know any formula.

 

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Thank you, really appreciate the help. 🙂

 

[Expert]

It would actually be -15.8 kJ x 18 because it is an exothermic reaction.