##4Na + O_2 rarr 2Na_2O##.

By the of this reaction if 5 mol natrium react, then 2.5 mol ##Na_2O## should result.

The molecular mass of natrium oxide is ##61.98## ##g*mol^(-1)##. If ##5## ##mol## natrium react, then ##5/2## ##molxx61.98## ##g*mol^(-1)## ##=## ##154.95## ##g## natrium oxide should result.

So what have I done here? First, I had a balanced chemical equation (this is the important step; is it balanced?). Then I used the stoichiometry to get the molar quantity of product, and converted this molar quantity to mass. If this is not clear, I am willing to have another go.

##4Na + O_2 rarr 2Na_2O##.

By the of this reaction if 5 mol natrium react, then 2.5 mol ##Na_2O## should result.

The molecular mass of natrium oxide is ##61.98## ##g*mol^(-1)##. If ##5## ##mol## natrium react, then ##5/2## ##molxx61.98## ##g*mol^(-1)## ##=## ##154.95## ##g## natrium oxide should result.

So what have I done here? First, I had a balanced chemical equation (this is the important step; is it balanced?). Then I used the stoichiometry to get the molar quantity of product, and converted this molar quantity to mass. If this is not clear, I am willing to have another go.