How do I figure this out? Suppose you had 2.0158grams of hydrogen (H2).
A.How many moles of hydrogen do you have?(do i just divide it by the atomic weight?)
B. How many moles of oxygen would react with this much hydrogen?
C. What mass of oxygen would you need for this reaction?
D. How many grams of water would you produce?

Question

How do I figure this out? Suppose you had 2.0158grams of hydrogen (H2). 
A.How many moles of hydrogen do you have?(do i just divide it by the atomic weight?)
B. How many moles of oxygen would react with this much hydrogen?
C. What mass of oxygen would you need for this reaction?
D. How many grams of water would you produce?

aaronq · Answer

A.How many moles of hydrogen do you have?(do i just divide it by the atomic weight?)

yes, divide by the molar mass of $H_2$

B to D:  first write and balance the chemical equation for the process

thatonegirl_ · Answer

when it asks how many moles would react with that much hydrogen, is hydrogen the product..? @aaronq

aaronq · Answer

nope, $H_2 +O_2\rightarrow H_2O+ energy$

ill let you balance it

thatonegirl_ · Answer

heres what i got
a. 1 mole
b.1 mole
c. 32 amu
d. 36.04 grams
did i do that right? @aaronq

aaronq · Answer

you need to first balance the equation

thatonegirl_ · Answer

yeah i did and i got$$2H _{2} O+O _{2} \rightarrow2H _{2} O$$

thatonegirl_ · Answer

@aaronq

aaronq · Answer

you mean: $2H_2+O_2→2H_2O$

so now, look at the coefficients, you used half as many oxygen molecules as hydrogen molecules in the reaction.

thatonegirl_ · Answer

yea thats what i meant oops. @aaronq

aaronq · Answer

so now answer B-D

thatonegirl_ · Answer

a) 2 moles..??
B) 1 mole
c) 32 amu
d) 36.04g @aaronq

aaronq · Answer

A was correct previously

aaronq · Answer

the rest are not

thatonegirl_ · Answer

To figure out the moles, you divide the mass of hydrogen by 1.01 correct? @aaronq

aaronq · Answer

you divide by the molar mass of the molecule, which is dihydrogen $H_2$, so the molar mass is 2*1.01=2.02

thatonegirl_ · Answer

And am i dividing the 2.0158 grams or the 2H2O? @aaronq

aaronq · Answer

$moles=\dfrac{mass}{molar~mass}$

$moles_{H_2}=\dfrac{mass_{H_2}}{molar~mass_{H_2}}=\dfrac{2.0158 ~\cancel g}{2.0158 ~\cancel g/mol}=1~mole$

thatonegirl_ · Answer

oh okay. so how do i figure out moles of oxygen that react with that? @aaronq

anonymous · Answer

bro thats really simple you've got 
n=m/M you've got the mass and the molar which 1 you get n

aaronq · Answer

you use the coefficients from the balanced reaction

$\sf \dfrac{moles~of~H_2}{H_2's ~coefficient}=\dfrac{moles~of~O_2}{O_2's ~coefficient}$

aaronq · Answer

set up that ratio with what you know (which is everything but moles of oxygen) and solve

thatonegirl_ · Answer

1/2? @aaronq sorry my teacher doesn't teach -.-

aaronq · Answer

yep thats right

aaronq · Answer

now the mass of oxygen ($O_2$), comes from the same formula, rearranged:

$mass=moles*molar~mass$

thatonegirl_ · Answer

so is that 16?

aaronq · Answer

yes 16 grams

aaronq · Answer

to find the mass of water, you'd first find moles with a ratio (like the one earlier), then the same formula.

thatonegirl_ · Answer

why wouldn't you just add the atomic weights of the molecule? @aaronq

aaronq · Answer

yeah, you can do that aswell (that's actually much much simpler)

aaronq · Answer

not atomic weights though, but masses

thatonegirl_ · Answer

so 2x(2x1.01)+16?

aaronq · Answer

(2x1.01)+16

only

thatonegirl_ · Answer

but in the balanced equations it's 2H2O?

aaronq · Answer

yeah but you only used 2 grams of $H_2$ and 16 g of $O_2$

the coefficients would only be used if you were finding moles first

thatonegirl_ · Answer

ah okay. Thank you so much :D

aaronq · Answer

no problem !