Welcome Guest Search | Active Topics |

 enthalpy confusion Previous Topic Next Topic
 Josh C #1 Posted : Wednesday, June 22, 2011 5:32:40 PM Rank: NewbieGroups: Registered Joined: 5/16/2011Posts: 2Thanks: 0 timesWas thanked: 0 time(s) in 0 post(s) Q1) if change in internal energy is (heat added to system) + (work on system), why is the change in enthalpy = change in internal energy + pressure * change in volume- i,e, work? isnt this already accounted for by the change in internal energy term? Back to top | Edit by user User Profile
 clarkeeuwes #2 Posted : Thursday, June 23, 2011 12:21:57 AM Rank: InstructorGroups: Registered Joined: 5/27/2011Posts: 2Thanks: 0 timesWas thanked: 0 time(s) in 0 post(s) Josh - you're absolutely right in recognizing these equations are closely related; if we plug them into one another (and keep our +/- signs consistent!), we see how the whole thing collapses into something we already know.Remember that in ΔE = q + w, when the system does work on the surroundings (expands) we consider this negative, so w is equal to (-PΔV).When we put that into our enthalpy equation ΔH = ΔE + PΔV, we see that ΔH = (q -PΔV) + PΔV, or ΔH = q. The mechanical work term completely drops out of the equation.This means that a change in enthalpy depends on the heat input. Back to top User Profile
 Users browsing this topic Guest
You cannot post new topics in this forum.
You cannot reply to topics in this forum.
You cannot delete your posts in this forum.
You cannot edit your posts in this forum.
You cannot create polls in this forum.
You cannot vote in polls in this forum.

Clean Slate theme by Jaben Cargman (Tiny Gecko)