Question

given Cl2 + 3F2 = 2ClF3,
how many grams of ClF3 form from 130.0 grams of Cl2 when F2 is in excess?

Answer 1

ok first calculate how many moles of Cl2 you have by using:
n = m/M
and then put that moles in ratio with product (hint: it takes one mole of Cl2 to get 2 moles of ClF3)
and from there you get how many moles of product you get and just reverse previously mentioned equation:
m = n * M