Question

The word standard in standard molar enthalpy change implies:
(A) temperature 298K
(B) pressure 1 atm
(C) temperature 298K and pressure 1 atm
(D) all temperatures and all pressures

Answer 1

Hint: Standard conditions are needed to relate the change in the thermodynamic quantities. These standard conditions are used as a reference. These are set by IUPAC.

Complete answer:
Enthalpy change is the term used to describe the energy exchange that takes place with the surroundings at a constant pressure and is given the symbol $\Delta H$. The standard enthalpy of a reaction (or standard heat of reaction) is the change in enthalpy of a chemical reaction under standard conditions; the actual number of moles are specified by the coefficients of the balanced chemical equation.
If we are to compare the enthalpy changes of a various reactions we must use standard conditions, such as known temperature, pressures, amounts and concentrations of reactants or products. The standard conditions are: A pressure of 1atm, a temperature of 298K. The standard conditions in most cases are known as STP. There are different types of standard enthalpies. They are Standard enthalpy of combustion, standard enthalpy of atomization, standard enthalpy of formation, Bond enthalpy.
So, the correct answer is “Option C”.

Note: Standard conditions for temperature and pressure are often necessary to define the standard reference conditions to express the volumes of gases and liquids and related quantities such as the volumetric flow and standard cubic meters per second.