CHEMISTRY COMMUNITY

I understand that at constant pressure, q= delta H, but do you use enthalpy of the reaction or enthalpy of formation?

That statement refers to the enthalpy of a reaction.

Yes. As long as you know the reaction is performed under constant pressure (if it's in an open beaker) then q=deltaH(rxn)

Would you have to take into account the number of moles of gas in relation to the balanced equation when solving for q ?

MSkye Goldwater 2K wrote:Would you have to take into account the number of moles of gas in relation to the balanced equation when solving for q ?

Yes it depends on how many moles the question says are reacting. For example, if the question says to find q when 3 moles of C2H6 are reacting, but your balance equation has only 1 mole of C2H6 reacting, then you must multiply the delta H of the reaction by 3 to find q.

as previously mentioned, it is important to note that the units for delta H are kj/mole. Therefore, when determining the enthalpy for a specific molecule or compound in a reaction, you need to take into account the stoichiometric coefficient to determine the enthalpy for that specific molecule or compound.