Question

Balance this redox reaction occurring in acidic media:
Cr2O7[2-](aq) + Cl[-](aq) <---> Cr[3+] (aq) + Cl2(g)

Answer 1

add 7 water molecule to the right hand side to balanace the number of oxygen. Multiply Cr(+3) by two to balance the number of Cr. Mulitiply Cl- by two to balance the number of chlorine atoms.
Cr2O7[2-](aq) +2 Cl[-](aq) <--->2 Cr[3+] (aq) + Cl2(g)+7H2O
Now balance that charges.
you have -4 charges on the left hand side, while +18 charges on the right hand side, there for add 14H+ on the left hand side to balance the charges
Cr2O7[2-](aq) +2 Cl[-](aq)+14H+ <--->2 Cr[3+] (aq) + Cl2(g)+7H2O

note that the oxidation number of hydrogen in water is +1

Answer 2

Thank you! :D That makes a lot more sense!