Consider the weak bases NH_3(aq) (K_b = 1.8 x 10^5) and NaF(aq) (K_a(HF) = 6.8 x

Question

Consider the weak bases NH_3(aq) (K_b = 1.8 x 10^5) and NaF(aq) (K_a(HF) = 6.8 x 10^4) in water. Which is the stronger base, NKh(ag) or F-(aq)? Explain your choice. Write the base hydrolysis equilibria for NH_3(aq) and F-(aq). Using the thermodynamic data provided, calculate DeltaHdegree (kJ), ASdegree (J/K), and DeltaGdegree (kJ) at 298.15 K for the chemical equilibria in part (b). Calculate the base hydrolysis constants, K_b, for NF_3(aq) and F-(aq) using your results in (b) and (c). One important industrial process to obtain hydrogen gas is by steam reforming of natural gas at temperatures 700-1100degreeC. An important chemical equilibrium in this process is the equilibrium between methane and water vapor with carbon monoxide and hydrogen gas. Write the chemical equilibrium between methane and water vapor as reactants and carbon monoxide and hydrogen gas as products, using integer coefficients. Evaluate DeltaHdegree (kJ), DeltaSdegree (J/K) at 298.15 K for the equilibrium in part (a). Assuming that DeltaHdegree and ASdegree do not change significantly with temperature, for what temperatures (in degreeC) is the equilibrium in part (a) spontaneous from left-to-right? Using the values of DeltaHdegree and DeltaSdegree from part (a), estimate the values of the equilibrium constant for the equilibrium in part (a) at 400 degreeC and 900 degreeC. How does your result in part (d) demonstrate LeChatelier's principle?

Explanation / Answer

1) a) NH3 is more basic than F -

          its concluded on basis of    Ka X Kbconjugate = 10-14   

For NH3 , Kb =1.8 x 10-5 ,   FOr F- , Kbconjugate = 10-14/6.8x10-4 = (1/6.8) x 10-10 so its smaller

b)   F- + H2O --------->   HF   + OH-   hydrolysis reaction

     NH3   + H2O ------>    NH4+    +   OH-      

i am solved two questions rest require additional data so please them separately with data

thanks

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