Which of the following best describes the term 'standard conditions' (Standard Temperature and Pressure, STP) in chemistry?

• A. A temperature of 0^ext{o}C (273.15 K) and a pressure of 1 bar
• B. A temperature of 25^ext{o}C (298.15 K) and a pressure of 1 bar
• C. A temperature of 0^ext{o}C (273.15 K) and a pressure of 1 atm
• D. A temperature of 25^ext{o}C (298.15 K) and a pressure of 1 atm

Answer: (C)

Verified step by step guidance

1. Understand that 'standard conditions' or Standard Temperature and Pressure (STP) in chemistry refer to a specific set of temperature and pressure values used as a reference point for experiments and calculations.
2. Recall that historically, STP has been defined as a temperature of 0^\text{o}C (273.15 K) and a pressure of 1 atm (atmosphere). This is the most commonly accepted definition in many chemistry contexts.
3. Note that 1 atm is equivalent to 101.325 kPa, and sometimes pressure is given in bars; 1 bar is slightly less than 1 atm (1 bar = 100 kPa). This distinction is important because some sources define standard pressure as 1 bar instead of 1 atm.
4. Recognize that the temperature of 25^\text{o}C (298.15 K) and pressure of 1 atm or 1 bar is often referred to as 'standard ambient temperature and pressure' (SATP), which is different from STP.
5. Therefore, the best description of STP is the set of conditions with temperature 0^\text{o}C (273.15 K) and pressure 1 atm, which matches the classical definition used in many chemistry calculations.