Cant Figure this One out?

Question

Using the following chemical equation:     P (s)   +   Cl₂ (g)    →  PCl₃ (l),

if 35.0 grams of chlorine react with excess phosphorus metal and 42.5 grams of phosphorous trichloride are produced in the lab, what is the percent yield?

Can you plz clearly explain/indicate the steps in your thought process in solving this problem, including labeling each number with units and chemical formula, using dimensional analysis, and reporting your answer to the correct number of significant figures?

Answer 1

First step is to balance the reaction, 2P + 3Cl₂ --> 2PCl₃. In the following I uses dimensional analysis to cancel no-longer-needed units, and I keep numbers to at least one more digit than the significant digits to avoid round-off error. Convert Cl₂ mass to moles: 35.0g Cl₂ *(1 mol Cl₂ /70.90g Cl₂) = 0.4937 mol Cl₂. For every 3 moles of Cl₂ gas, 2 moles of PCl₃ are produced: 0.4937 mol Cl₂ *(2 mol PCl₃ /3 mol Cl₂) = 0.3291 mol PCl₃. Convert this to mass: 0.3291 mol PCl₃ *(137.3g PCl₃ /1 mol PCl₃) = 45.19g PCl₃ theoretical yield. Percent yield = 100*actual/theoretical = 4250/45.19 = 94.0% to 3 sig figs.