Question
plz help!!!
Assess the feasibility of the reaction N2H4(g) + 2 OF2(g) right arrow N2F4(g) + 2H2O (g) by determining each of the following quantities for this reaction at 25 degree C. delta S degree (The standard molar entropy of N2F4(g) is 301. 2 JK-1. ) delta H degree (Use data from Table 10. 3 in the textbook and F - O and N - F bond energies of 222 and 301 kJ mol -1 respectively. ) delta G degree
Explanation / Answer
For a reaction in which the reactants and products end up at the same temperature and pressure, it is the sign of the Gibbs free energy change of the reaction that tells you whether the reaction is spontaneous (thermodynamically favored to proceed in the forward direction) or not. The Gibbs free energy change is related to the enthalpy and entropy changes by: ?G = ?H - T*?S where T is the temperature (in kelvins). If ?G is < 0 the reaction is spontaneous, if ?G > 0 the reaction is not spontaneous, and if ?G = 0, the reactants and products are in equilibrium. If ?H < 0, the reaction is enthalpically favored, but if ?S < 0, the entropy change counters this because of the negative sign in front of the T*?S term. As long as: ?G = ?H - T*?S < 0 ?H 0. If ?H > 0 and ?S < 0, the reaction can never be spontaneous If ?H < 0 and ?S > 0, the reaction is always spontaneous If ?H > 0 and ?S > 0, the reaction is spontaneous when T > ?H/?S If ?H < 0 and ?S < 0, the reaction is spontaneous when T < ?H/?S Note that a "spontaneous reaction" may be kinetically inhibited, and may only progress at a geologically slow rate in the absence of a catalyst, an energy input, or other perturbation (e.g., a container of H2 and O2 gas will just sit there at room temperature; the reaction to form water, which is thermodynamically favored (i.e., spontaneous) won't occur at a measurable rate. If you add a catalyst, or provide a little energy input (e.g., a spark or a flame), the reaction will then proceed quite rapidly!)