Standard state

Definition

The standard state of a substance is its pure form at a specified temperature (usually 298 K) and pressure (1 bar). It serves as a reference point for thermodynamic calculations.

5 Must Know Facts For Your Next Test

1. The standard state is typically defined at 298 K and 1 bar pressure.
2. It provides a baseline for measuring enthalpy changes in chemical reactions.
3. In the standard state, elements are in their most stable form (e.g., O2 for oxygen, N2 for nitrogen).
4. Standard enthalpy of formation refers to the enthalpy change when one mole of a compound forms from its elements in their standard states.
5. Gases in their standard state are considered ideal gases.

Review Questions

• What temperature and pressure define the standard state?
• Why is the concept of the standard state important in thermochemistry?
• How does the standard state apply to the calculation of enthalpy changes?

Related terms

Enthalpy: A measure of heat content in a system at constant pressure; denoted as $H$.

Standard Enthalpy of Formation: The enthalpy change when one mole of a compound forms from its elements in their standard states.

Ideal Gas: A hypothetical gas whose molecules occupy negligible space and have no interactions, obeying the ideal gas law exactly.