# What is standard potential? Is standard potential for a particular substance is constant ( standard potential for zinc = #-0.76# v ) ? How to calculate the same?

##### 1 Answer

See below.

#### Explanation:

There are two types of standard potential: standard cell potential and standard half-cell potential.

**Standard cell potential**

**Standard cell potential** is the **potential** (voltage) of an electrochemical **cell** under **standard** conditions (concentrations of 1 mol/L and pressures of 1 atm at 25 °C).

In the above cell, the concentrations of

**Standard Half-cell potentials**

The problem is, we don’t know what portion of the voltage comes from the zinc half-cell and how much comes from the copper half-cell.

To get around this problem, scientists have agreed to measure all voltages against a **standard hydrogen electrode** (SHE), for which the standard half-cell potential is defined as 0 V.

The

We can measure the half-cell potentials of many reactions against the SHE and put them in a list of **standard half-cell potentials**.

If we list them all as reduction half-reactions, we have a table of **standard reduction potentials**. Here is a short list

**Calculating an unknown half-cell potential**

We can write the equations for the half-cells in the first image.

#color(white)(mmmmmmmmmmmmmm)E^@//V#

#"Cu"^"2+" + 2"e"^"-" → "Cu"; color(white)(mmmmmm)?#

#"Zn" → "Zn"^"2+" +2"e"^"-"; color(white)(mmmmm)"+0.763"#

#stackrel(————————————)("Cu"^"2+" + "Zn" → "Cu" + "Zn"^"2+");color(white)(m)"+1.100"#

If we find the cell potential to be 1.100 V, we know that 0.763 V comes from the