Diamond is an elementary substance.yet its standard heat of formation is not taken as zero why?

This question has Statement I and Statement II. Of the four choices given after the Statements, choose the one that best describes the two Statements. Statement-I : Enthalpy and entropy of any elementary substance in the standard states are taken as zero. Statement-II : At absolute zero, particles of the perfectly crystalline substance become completely motionless.

Which of the following state of bromine will have standard heat of formation to be equal to zero liquid bromine,solid bromine,gaseous bromine molecules.

For which element in each of the following pairs has the standard heat of formation of zero? (i) [O_(2)(g),O_(3)(g)] (ii) [ Cl_(2)(g),Cl(g)] (iii) [S("s, rhombic"),S(s", monoclinic")] ?

Between O_(2)(g) and O_(3)(g) , whose standard enthalpy of formation (DeltaH_(f)^(0)) is taken as zero at 1 atm and 25^(@)C ?

In which of the following reactions the standard heat of reaction is equal to the standard heat of formation of CaBr_(2)(s) at 25^(@)C ? (i) Ca(s)+Br_(2)(l)toCaBr_(2)(s) (ii) Ca(s)+Br_(2)(g)toCaBr_(2)(g) .

This question has Statement I and Statement II. Of the four choices given after the Statements, choose the one that best describes the two Statements. Statement-I : The standard free energy changes of all spontaneously occuring reactions are negative. Statement-II : The standard free energies of the elements in their standard states at 1 bar and 298 K are taken as zero.

In which of the following standard enthalpy of formation (Delta H_(f)^(0)) is zero ?

The value of standard hydrogen electrode potential is taken as zero, because -

Although diamond is a covalent substance, its melting point is very high-explain.

For which of the following reactions does the standard enthalpy of reaction represent the standard enthalpy of formation of CH_(4)(g) ? Explain it. (a) C(diamond, s) +4H_(2)(g)toCH_(4)(g) (b) C(graphite, s) +O_(2)(g)toCH_(4)(g) .