CHM 132 Chapter Notes - Chapter 9: Royal Aircraft Factory F.E.2, Enthalpy

• School: University of Rochester
• Department: Chemistry
• Course: CHM 132
• Professor: Kara Bren

Document Summary

Hess"s la(cid:449) the change in enthalpy is the same between products and reactants whether the reaction takes place in one step or through a series of steps. If a reaction is (cid:396)e(cid:448)e(cid:396)sed, the sig(cid:374) of h is (cid:396)e(cid:448)e(cid:396)sed: the (cid:373)ag(cid:374)itude of h is di(cid:396)e(cid:272)tly p(cid:396)opo(cid:396)tio(cid:374)al to the (cid:395)ua(cid:374)tities of (cid:396)ea(cid:272)ta(cid:374)ts a(cid:374)d products in a reaction. If the coefficients in a balanced reaction are multiplies by a(cid:374) i(cid:374)tege(cid:396), the (cid:448)alue of h is (cid:373)ultiplied (cid:271)y the sa(cid:373)e integer. Hints for using hess"s law: ge(cid:374)e(cid:396)ally to use hess"s la(cid:449) o(cid:374)e (cid:373)ust (cid:373)a(cid:374)ipulate (cid:448)a(cid:396)ious e(cid:395)uatio(cid:374)s u(cid:374)til combined they equal the desired reaction. Manipulation includes reversal and multiplying the reactions by integers: example: For a gas, the standard state is a pressure of 1atm. For a substance present in a solution, the standard state is a concentration of exactly 1m at an applied pressure of 1atm. For a pure substance in a condensed state, the standard state is the pure liquid or solid.