Step-by-step explanation:
The equation of the reaction is given as;
12C + 16 H2 --> 4 C3H8
a. Simplify the equation;
The coefficients are 12, 16 and 4.
4 is a common factor, so divide all through by 4.
12/4 = 3, 16/4 = 4, 4/4 = 1
The equation is given as;
3 C + 4 H2 --> C3H8
b. If 21 moles of C3H8 are formed, how many moles of C was needed.
From the reaction;
3 mol C atoms reacts to form 1 mol of C3H8
x mol would react to form 21 moles of C3H8
3 = 1
x = 21
x = 21 * 3
x = 63 moles