Question

For the reaction, 2cr2+ + cl2(g) ---> 2cr3+ + 2cl- e cell (standard conditions) = 1.78v calculate ecell (standard conditions) for the related reaction cr3+ + cl- ----> cr2+ + 1/2cl2(g)

A. 0.89 v
B. - 0.89 v
C. 1.78 v
D. - 1.78 v
E. Non of these

Answer 1

-1.78 V

Step-by-step explanation:

There are several rules required to calculate the cell potential:

• given standard cell potential, we may reverse the equation: the products of a given reaction become our reactants, while reactants become our products in the reversed equation. For a reversed equation, we change the sign of the cell potential to the opposite sign;
• if we multiply the whole equation by some number, this doesn't influence the cell potential value. It only produces a different expression in the equilibrium constant.

That said, notice that the initial reaction with respect to the final reaction is:

• reversed: chromium(III) cation and chloride anion become our reactants as opposed to the products in the initial reaction, so we change the sign of the cell potential to a negative value of -1.78 V;
• each coefficient is multiplied by a fraction of
  `(1)/(2)`. It doesn't influence the value of the cell potential.

Thus, we have a cell of E = -1.78 V.