Find the amount of oxide that forms when 7.1 g of chlorine reacts with oxygen.

Given:
m (Cl2) = 7.1 g

To find:
m (oxide) -?

1) Write the reaction equation:
2Cl2 + 7O2 => 2Cl2O7;
2) Calculate the molar mass of Cl2:
M (Cl2) = Mr (Cl2) = Ar (Cl) * N (Cl) = 35.5 * 2 = 71 g / mol;
3) Calculate the amount of substance Cl2:
n (Cl2) = m (Cl2) / M (Cl2) = 7.1 / 71 = 0.1 mol;
4) Determine the amount of substance Cl2O7:
n (Cl2O7) = n (Cl2) = 0.1 mol;
5) Calculate the molar mass of Cl2O7:
M (Cl2O7) = Mr (Cl2O7) = Ar (Cl) * N (Cl) + Ar (O) * N (O) = 35.5 * 2 + 16 * 7 = 183 g / mol;
6) Calculate the mass of Cl2O7:
m (Cl2O7) = n (Cl2O7) * M (Cl2O7) = 0.1 * 183 = 18.3 g.

Answer: The mass of Cl2O7 is 18.3 g.