Explain why the enthalpy of formation and the entropy of formation of an element in its standard state at 298 K and 1 bar pressure are not equal ?

The enthalpies of all elements in their standard state are :

Standard molar enthalpy of formation of CO_2 is equal to:

Define and illustrate standard enthalpy of formation.

The standard heat of formation of diamond, although an elementary substance, is not taken as zero. Explain why ?

Explain, why oxidation states of transition elements first increases from Sc to Mn and then decreases ?

(i) Write the balanced equations to represent what happens when (a) acidified potassium permanganates reacts with hydrogen sulphide ? (b) acidified potassium dichromate solution reacts with iron (II) solution (ionic equation) ? (ii) The figure given below illustrates the first ionisation enthalpies of first, second and third series of transition elements. (a) Which series amongst the first, second and third series of transition elements have the highest first ionisation enthalpy and Why ? (b) Why there is a fall in IE_(2) from Cr to Mn and from Cu to Zn ? Explain.

Enthalpies of elements in their standard states are taken as zero. Hence the enthalpy of formation of a compound

AB, A_2 and B_2 are diatomic molecules. If the bond enthalpies A_2 AB and B_2 are in the ratio 1:1:0.5 and the enthalpy of formation of AB fron A_2 and B_2 is -100 kJ mol^-1 , what is the bond enthalpy of A_2 :

The enthalpy of formation of ammonia gas at 298 K is -46.11kJ mol^-1 . The equation to which this value related is: