If heat and enthalpy are by definition different, then why in some problems (like 93), we use them interchangeably? For example, we calculate the work in part a, then the delta H in part b, then in part c it asks us for delta U (which is q+w). But the solutions manual simply added part a (w) and part b (delta H) together. So delta H and
q are interchangeable even though they are not the same by definition?
q and delta H interchangeable in calculations?
Moderators: Chem_Mod, Chem_Admin
-
- Posts: 59
- Joined: Fri Sep 29, 2017 7:07 am
-
- Posts: 50
- Joined: Fri Sep 29, 2017 7:05 am
Re: q and delta H interchangeable in calculations?
Delta H is only equivalent to the heat absorbed/released (aka q) when the system has a constant pressure and no nonexpansion work.
-
- Posts: 52
- Joined: Fri Sep 29, 2017 7:06 am
Re: q and delta H interchangeable in calculations?
They are equivalent only under certain conditions, in this case at constant pressure.
-
- Posts: 50
- Joined: Fri Sep 29, 2017 7:04 am
- Been upvoted: 2 times
Re: q and delta H interchangeable in calculations?
q and ∆H are only equal to each other when pressure is constant. This gives rise to the equation for change in internal energy of a reaction that happens in a sealed container. If you substitute ∆H for q, the change in internal energy equation becomes ∆U = ∆H - w, or ∆U = ∆H -P∆V.
-
- Posts: 50
- Joined: Thu Jul 27, 2017 3:00 am
- Been upvoted: 1 time
Re: q and delta H interchangeable in calculations?
In addition, because the amount of heat absorbed or released at a constant pressure is defined as the enthalpy, we can write that q = ∆H.
Who is online
Users browsing this forum: No registered users and 3 guests