(1) I'll explain through examples :

Calculate the equilibrium molarities of H2, I2, and HI

                              H2(g) + I2(g) <--> 2 HI(g)
Initial..................... 0.05.... 0.06 ...........0
Change...................- x ......- x..............+x
Equilibrium.......... 0.05 - x.. 0.06-x...........x

Equilibrium constant, K_c = [HI]2 / [H2] [I2] = 58.6
......................................… = [x]² / [0.05-x] [0.06-x] = 58.6

Solve for x to get the change in the number of moles, and subsequently the number of moles of each compound in equilibrium

Molarity of H2 = [0.05-x] / 1.00L
Molarity of I2 = [0.06-x] / 1.00L
Molarity of HI = x / 1.00L

(2)

Equivalent weight is the atomic weight of an element or radical divided by the valence it assumes in a chemical compound.

5H2SO4+8NaI=4Na2SO4+H2S+4H2O+4I2