1. The problem statement, all variables and given/known data Determine the volume of oxygen gas required to completely combust 3.5mole of propane in a barbecue at standard pressure and 28.0°C. 2. Relevant equations ##PV = nRT## 3. The attempt at a solution My first question is, is the work I've done here still correct? http://gyazo.com/3a22ee323ec1edff0ea071255cf698ac I'm a bit confused here. If i take the standard mole ratio route, I get a completely different answer. I would find that 17.5mole of oxygen would be needed for 3.5mole of propane. Then using the relevant equation I get 437.72925L = 400L because 100kPa only has 1 significant digit. This answer is clearly very far off. This leads me to believe the question is intending me to do the work as I've shown in the image above. Why does this incredibly different answer occur? Is it merely a fault of significant error? Or am i wrong completely and the mole route is appropriate (which really wouldn't make sense)?