Calculate the amount of the substance and the mass of the formed sodium sulfide Na2S

Calculate the amount of the substance and the mass of the formed sodium sulfide Na2S, if 5 mol of sodium entered into a reaction with oxygen. Reaction scheme: Na + S = Na2S

Given:
n (Na) = 5 mol

To find:
n (Na2S) -?
m (Na2S) -?

Solution:
1) Write the equation of a chemical reaction:
2Na + S => Na2S;
2) Using the periodic system of D.I.Mendeleev, calculate the molar mass of Na2S:
M (Na2S) = Mr (Na2S) = Ar (Na) * 2 + Ar (S) = 23 * 2 + 32 = 78 g / mol;
3) Determine the amount of Na2S substance (taking into account the coefficients in the reaction equation):
n (Na2S) = n (Na) / 2 = 5/2 = 2.5 mol;
4) Calculate the mass of Na2S:
m (Na2S) = n (Na2S) * M (Na2S) = 2.5 * 78 = 195 g.

Answer: The mass of Na2S is 195 g.