What is the circle on top of variables in chem?
Like dS^o, dH^o, and dG^o. Do they represent standard state? Or standard condition? What's the difference between these two anyway?
Like dS^o, dH^o, and dG^o. Do they represent standard state? Or standard condition? What's the difference between these two anyway?
1 Answer
Circle refers to standard conditions, Plimsoll symbol refers to standard state.
Explanation:
Usually:
The circle superscript refers to standard conditions.
The Plimsoll symbol (circle with a line through) refers to standard state . ⦵
You will find that they are used interchangeably, which is a bit confusing. But as long as you can recognise the difference between standard state and standard conditions, and when to use each, you should be okay.
Standard conditions , represented by the initialism STP (stnading for standard temperature pressure) refers to a temperature of
Standard State supplies several different conditions, including:
- The standard state temperature is
#25°C# (#298 K# ). Sometimes#0^@C# is used for standard state, but if another temperature is not supplied assume#298 K# . - All gases are at
#1 atm# pressure. - All liquids and gases are pure.
- All solutions are at
#1M# concentration. - The energy of formation of an element in its normal state is defined as zero.
Standard state is used in thermodynamic calculations for entropy, enthalpy, Gibbs, equilibrium constant etc.
