A compound is formed when 171.2 g of carbon reacts with 28.8 g of hydrogen. What is the mass percent of hydrogen in the compound

Following the law of conservation of mass, the mass percent of hydrogen in the resulting compound is 14.4% (wt/wt). This is assuming that all of the carbon reacts with all of the hydrogen. The solution is as follows:

mass % = mass hydrogen*100/total mass = 28.8*100 / (28.8+171.2) = 14.4%