calculate percent of weight change

Question

Calculate the percent of weight change for a reaction which combines 5.0 grams of reactant A with 2.0 grams of reactant B and produces 7.5 grams of product C. Show all work please

Answer 1

So this reaction isn't done in a closed system.  We started with 7.0 g of reactant (5.0 + 2.0) and ended with 7.5 g of product.  Therefore, the reaction used 0.5 g of ambient air.  The percentage change is just the amount of change divided by total original times 100, or:

 

0.5/7.0  * 100 = 7%