How much mass of silica reacts if it is known that 788.4 kJ of heat was released by its reaction with fluorine, but the thermochemical
equation of the reaction is as follows
SiO2 + 2F2 ---> SiF4 + O2 + 657kJ​

the answer is c

tell me if wrong

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.