It is known that  (Pb2+/Pb) = -0.126 2V, Ka (HAc)=1.76×10-5, there is a primary battery: (-) Pb│Pb2+(1mol·L-1)‖H+(1mol·L-1)│H2(1 00kPa),Pt (+)
Question: (1) In the standard state, can the 2H+ + Pb = H2 + Pb2+ reaction occur? (2) If NaAc is added to the H+ solution and the concentration of HAc and Ac- are both 1mol·L-1 after equilibrium, The partial pressure of H2 is 100kPa, does the reaction direction change?

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answer: semi-infinite solid initially at a uniform temperature of 400 ◦c is cooled at its surface by convection. the cooling fluid at a constant temperature of 200 ◦c has a convective coefficient (ha) of 250 w/m2.k. the physical properties of the solid: k = 20 w/m.k and α = 4 * 10-5  m2/s. using δx = 0.04 m and δt = 10 s. write the finite difference equations describing the transient heat transfer of the first five δx and the temperature profile after 30 s.