Chemistry Talk Chemistry Talk    FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  question from ap chem          Chemistry Talk Forum Index -> Chemistry Talk View previous topic :: View next topic   Author Message john Guest Posted: Wed May 09, 2007 11:37 am    Post subject: question from ap chem a samle problem from ap chem handout. 2 SO2 (g) + O2 (g) -> 2 SO3(g) A mixture of gases containing 0.20 mol of SO2 and 0.20 mol of O2 in a 4.0 L flask reacts to form SO3. If the tempertaure is 25C. what is the pressure in the flask after reaction is complete? answer. ( 0.3 (0.082) (298) ) / 4 atm but it seems to me the answer shoudl be ( 0.4 (0.082) (298) ) / 4 atm since P = ( n1 + n2 )( RT/V ) = (0.2 + 0.2 )( RT/V ) Thanks for any input. Back to top   Ads Advertising Sponsor Uncle Al Guest Posted: Wed May 09, 2007 8:05 pm    Post subject: Re: question from ap chem john wrote: Quote: a samle problem from ap chem handout. 2 SO2 (g) + O2 (g) -> 2 SO3(g) A mixture of gases containing 0.20 mol of SO2 and 0.20 mol of O2 in a 4.0 L flask reacts to form SO3. If the tempertaure is 25C. what is the pressure in the flask after reaction is complete? answer. ( 0.3 (0.082) (298) ) / 4 atm but it seems to me the answer shoudl be ( 0.4 (0.082) (298) ) / 4 atm since P = ( n1 + n2 )( RT/V ) = (0.2 + 0.2 )( RT/V ) Thanks for any input. Look at the stoichiometry. 0.2 mol SO2 will react with 0.1 mole of O2. You don't need any RT/V diddles - it cancels. (0.2 mol + 0.1) mole reactants --> 0.2 mol product plus 0.1 mol background unchanged. Wrote procedure is good, so is understanding what you are doing. Do not look at the trees to the exclusion of the forest - or you get Canadian mangement of the Grand Banks fishery (utter destruction for the nicest of possible reasons, with voluminous punctilious documentation to the contrary until physical reality voted). -- Uncle Al http://www.mazepath.com/uncleal/ (Toxic URL! Unsafe for children and most mammals) http://www.mazepath.com/uncleal/lajos.htm#a2 Back to top   Ads Advertising Sponsor Angelo Guest Posted: Wed May 09, 2007 8:24 pm    Post subject: Re: question from ap chem On 9 Mag, 08:37, john <johnboy98...@yahoo.com> wrote: Quote: a samle problem from ap chem handout. 2 SO2 (g) + O2 (g) -> 2 SO3(g) A mixture of gases containing 0.20 mol of SO2 and 0.20 mol of O2 in a 4.0 L flask reacts to form SO3. If the tempertaure is 25C. what is the pressure in the flask after reaction is complete? answer. ( 0.3 (0.082) (298) ) / 4 atm In that answer, as well below, there should be a typo: P = ( 0.3 (0.082) (298) ) / 4 L Having a fixed volume V and a fixed temp T, what makes up the pressure? Is there a limiting reactant, or IOW, is there a reactant that remains unchanged? Keep also in mind that in a chemical reaction there's no law of mole conservation. Quote: but it seems to me the answer shoudl be ( 0.4 (0.082) (298) ) / 4 atm since P = ( n1 + n2 )( RT/V ) = (0.2 + 0.2 )( RT/V ) That would be the P *before* the beginning of the reaction (!) Quote: Thanks for any input. Ciao, Angelo Back to top   Ads Advertising Sponsor Display posts from previous: All Posts1 Day7 Days2 Weeks1 Month3 Months6 Months1 Year Oldest FirstNewest First         Chemistry Talk Forum Index -> Chemistry Talk All times are GMT Page 1 of 1   Jump to: Select a forum Chemistry Talk----------------Chemistry Talk  You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum 97 Attacks blocked Powered by phpBB © 2001, 2005 phpBB Group