Question

One version of the First Law of Thermodynamics is expressed as Delta E = q + W Which gives the sign convention for this relationship that is usually used in chemistry? C_2 H_5 OH_(l) + 3 O_2(g) rightarrow 2CO_2(g) + 3H_2 O_(g) At 298 K, the change in enthalpy, Delta H, for the reaction above is approximately equal to (A) Delta E + RT (B) Delta E - 2 RT (C) Delta E + 2 RT (D) 5RT - Delta E (E) 2RT - Delta E

Answer 1

Q is positive if heat is added to the system, and negative if heat is removed: W is positive if work done by the system, & negative if work is done on the system. (E) + . . . . delta E = delta H - delta nRT C_2H_5on(l) + 3O_2 (g) rightarrow 2 Co_2 (g) + 3 H_2O(g) delta n = (2 + 3) - 3 = 2 delta E = delta H- 2 RT delta H = delta E + 2RT