Cell voltages and half-cell potentials are often compeared under standard conditions called the standard state at a specified temperature (298K). The standard state requires all reagents to be pure with all gases at unit fugacity, all ions at unit activity and all electrical connections between half-cells to be made with platinum. Suppose following are half cell reaction, with respective emf (s) are -0.25 V and -0.3V. Cell reaction I underset("1 atm")(Pt(H_(2))|HCl) Cell reaction II underset("1 atm")(Pt(H_(2))|H_(2)SO_(4)) Zinc gives H_2 with H_2SO_4 and HCI but not with HNO3 because:

Cell voltages and half-cell potentials are often compeared under stand

1.	Cell voltages and half-cell potentials are often compeared under standard conditions called the standard state at a specified temperature (298K). The standard state requires all reagents to be pure with all gases at unit fugacity, all ions at unit activity and all electrical connections between half-cells to be made with platinum. Suppose following are half cell reaction, with respective emf (s) are -0.25 V and -0.3V. Cell reaction I underset("1 atm")(Pt(H_(2))\|HCl) Cell reaction II underset("1 atm")(Pt(H_(2))\|H_(2)SO_(4)) Zinc gives H_2 with H_2SO_4 and HCI but not with HNO3 because:
Answer» zinc acts as OXIDIZING agent when reacts with `HNO_3` `HNO_3` is a weaker ACID than `H_2SO_4 and HCI` in electrochemical series zinc is above than HYDROGEN `NO_(3)^(-)` is REDUCED in PREFERENCE to hydronium ion Answer :D