osprey099

7+ Year Member
Jan 27, 2011
1,388
43
Status
Resident [Any Field]
If I have the equation: X(aq) + H2O (l) <-> Y(aq) + Z(aq), is the rate equation Rate = k[X] or is it Rate = k[X][H2O]? I think it's Rate = k[X] but in TBR Kinetics Passage 7, Questions 46 and 47, they put [H2O] into the equation..
 

circulus vitios

10+ Year Member
7+ Year Member
Jul 18, 2008
6,255
1,629
Is that the real reaction, or just your own genericized version? Water does appear in the equation if it's a reactant. It does not appear if it's a solvent.
 

Sandstorm

5+ Year Member
Oct 10, 2011
460
2
Status
Medical Student
If you have pure water, the concentration will be 1M no matter if you have a microliter or a kiloliter.
 

slz1900

7+ Year Member
Nov 10, 2011
311
52
Status
Resident [Any Field]
Incorrect. Pure solids and liquids do not appear.
Not true. You ignore liquids IF their concentration is not changing. We don't know whether or not that is the case here. It would depend on whether or not there was a lot of water on the reactant side starting out. And even if you do leave it out, the reaction would still be a second order, pseudo first order reaction.
 

Mehd School

5+ Year Member
May 2, 2012
2,287
672
West Coast
Status
Resident [Any Field]
Concentrations of liquids and solids do not change in these instances, and therefore should not be included in the reaction rate.