A Level Chemistry OCR Practice Exam

What are standard conditions typically defined as?

1. A pressure of 100 kPa, temperature of 373 K

2. A pressure of 100 kPa, temperature of 298 K and 1 mol dm-3 concentration

3. Normal atmospheric pressure and a temperature of 0 °C

4. A pressure of 1 atmosphere and 25 °C

The correct answer is: A pressure of 100 kPa, temperature of 298 K and 1 mol dm-3 concentration

Standard conditions are typically defined as a pressure of 100 kPa, a temperature of 298 K (which is equivalent to 25 °C), and a concentration of 1 mol/dm³ for solutions. This set of conditions is used as a reference point in many scientific measurements and calculations, allowing for consistency when comparing the behavior of different substances or reactions. In particular, the temperature of 298 K is critical since it's commonly used in thermodynamic calculations, and it aligns with the temperature defined by the International Union of Pure and Applied Chemistry (IUPAC) for standard temperature and pressure (STP). The pressure is set to 100 kPa, which is slightly different from 1 atmosphere but is meant to indicate a standardized environment for experiments. This definition is important in the context of solution chemistry and gas calculations, enabling chemists to predict the outcomes of reactions under these specified conditions. The presence of 1 mol/dm³ concentration further aids in creating a common ground for studying reactions involving solutions. While the other choices mention relevant conditions, they do not fulfill all criteria for standard conditions as established in the context of chemistry.