Significant Figures: Answer to 6.45 mol H2 Conversion

[linuxux]

When i have a conversion fact such as,

6.45 mol H_{2\left(g\right)}\times\frac{2 mol HBr_{\left(g\right)}}{2 mol H_{2\left(g\right)} }= 12.9 mol HBr_{g}

how many significant figure should the answer have?, I am thinking one.

 

[cristo]

You've not written one sig fig though, you've written your answer with three. I would suggest to use 3 sig figs since the number of moles of hydrogen are accurate to 3 sig figs, and I presume that 2 is exactly two (i.e. 2.000), so giving 3 sig figs in the answer (like you've done; 12.9) will be as accurate as possible.

 

[linuxux]

thanks cristo.