A reaction profile (not to scale!) for the reaction 20203 +0 is shown below: E (KJ) O2 + O2 411 03 + O Reaction Coordinate 392 Which of the following are true? Choose all that apply. The energy of the products is higher than the energy of the reactants. The value of delta E in the presence of a catalyst would be smaller than 392 kJ. The value of Ea in the presence of a catalyst would be lower than 411 kJ. AE is negative. O The reaction is endothermic.

Silicon forms a series of compounds analogous to the al-kanes and having the general formula SinH2n+2. The first of these compounds is silane, SiH4, which is used in the electronics industry to produce thin ultrapure silicon films. SiH4(g) is somewhat difficult to work with because it is py-ropboric at room temperature—meaning that it bursts into flame spontaneously when exposed to air. (a) Write an equation for the combustion of SiH4(g). (The reaction is analogous to hydrocarbon combustion, and SiO2 is a solid under standard conditions. Assume the water produced will be a gas.) (b) Use the data from Appendix E to calculate ? for this reaction. (c) Calculate G and show that the reaction is spontaneous at 25°C. (d) Compare G for this reaction to the combustion of methane. (See the previous problem.) Are the reactions in these two exercises enthalpy or entropy driven? Explain.

For the following reaction C(s)+2H2(g)CH4(g) K=0.26 at 1000C (3 significant figures). What is the equilibrium constant at 750C (3 significant figures)?

9.96 Most first aid "cold packs" are based on the endothermic dissolution of ammonium nitrate in water: NH4NO3(s)NH4+(aq)+NO3(aq) H= 25.69 kJ A particular cold pack contains 50.0 g of NH4NO3 and 125.0 g of water. When the pack is squeezed, the NH4NO3dissolves in the water. If the pack and its contents are initially at 24.0°C, what is the lowest temperature that this bag could reach? (Assume that the ammonium nitrate solution has a specific heat of 4.25J g-l K-l, and that the heat capacity of the bag itself is small enough to be neglected.)