What temperature and pressure define standard temperature and pressure (STP)?

Standard temperature and pressure (STP) is defined as a temperature of 0 degrees Celsius (273.15 Kelvin) and a pressure of 1 atmosphere. This standard condition is crucial in various scientific calculations, such as those involving gas laws, as it provides a common reference point for experimental and theoretical work involving gases.

Using this definition, when working with ideal gas equations or performing stoichiometric calculations involving gases, scientists can reliably predict behavior under the consistent conditions of STP. It's important to note that STP may vary slightly depending on different scientific contexts, but the commonly accepted definition for the purposes of chemistry, especially in relation to the Ideal Gas Law, is indeed 0°C and 1 atm.