Thermochemical Standards: Arbitrary Definitions

Question 1

Liquids and solids

Answer 1

For pure substance in liquid/solid phase, STD state is pure liquid or pure solid

Question 2

Gases

Answer 2

For gas, STD state is pressure of 1 bar (formerly 1 atm). In mixture of gases, partial pressure of each STD state gas is 1 bar

Question 3

Aqueous species

Answer 3

For dissolved substance, STD state is molar concentration of 1 M.

Question 4

STD molar enthalpy of formation

Answer 4

Enthalpy change for reaction in which one mole of substance in specified state is formed from elements in STD states. Is 0 only for element in its most stable form.

Question 5

STD enthalpy change

Answer 5

Change in enthalpy when specified numbers of moles of reactants are completely converted to specified numbers of moles of products