Question

Can someone help? What are the equations I should be using?

Consider the complete reaction of 15.2 g of chromium solid with excess oxygen gas. What mass of product forms?
4 Cr(s) + 3 O2(g) → 2 Cr2O3(s)

Answer 1

so do you know how to start off this problem?

Answer 2

I used to, but I haven't tried a problem like this for a while

Answer 3

ah ok so first you have to balance the equation but it looks like it's balanced
so the next step is you have to convert everything into moles. So what is 15.2 g of chromium in moles?

Answer 4

0.2923, right?

Answer 5

yup

Answer 6

alright now that we have the moles and we know that have excess oxygen and thus don't have to solve for the limiting reactant we can convert the moles of chromium to Cr2O3. Do you know how to do so?

Answer 7

Ahhhh...... It's on the tip of my tongue, but no, sorry.

Answer 8

No problem. So we look at the balanced equation we have and realize that for every 4 moles of Cr we make 2 moles of Cr2O3. So if we have 0.2923 moles of Cr, we will make how many moles of Cr2O3?

Answer 9

I remember now, you multiply by the ratio, right? So .14615?

Answer 10

Cause the equation would be .2923 times 4/2, which reduces to 2/1, which would make it .14615

Answer 11

exactly!

Answer 12

And then do you just change the moles to grams?

Answer 13

so what's our next step?

Answer 14

exactly you got it!

Answer 15

everything clear?

Answer 16

So the answer would be 22.21

Answer 17

Or 22.2 using sig figs

Answer 18

But...and I think you probably need to think about sig figs!

Answer 19

exactly!

Answer 20

Thank you!

Answer 21

No problem