Table of Contents
Can the enthalpy of formation be zero?
The standard enthalpy of formation of any element in its most stable form is zero by definition. (which is pronounced “delta H eff naught”). The standard enthalpy of formation of any element in its standard state is zero by definition. Therefore, O 2(g), H 2(g), and graphite have ΔHof values of zero.
Does gas have enthalpy of formation?
All elements in their standard states (oxygen gas, solid carbon in the form of graphite, etc.) have a standard enthalpy of formation of zero, as there is no change involved in their formation.
Why is the enthalpy of formation always zero?
The enthalpy of formation for an element in its elemental state will always be 0 because it takes no energy to form a naturally-occurring compound.
What is the standard enthalpy of formation equal to zero?
And since there’s no change, there’s no change in enthalpy. Therefore, the standard enthalpy of formation is equal to zero. And this is true for the most stable form of any element. The standard enthalpy of formation of the most stable form of any element is zero since you’d be making it from itself.
Is enthalpy of formation always negative?
It’s not always negative. Sometimes it’s positive. A negative ΔHof indicates that the formation of a compound is exothermic—the amount of energy it takes to break bonds is less than the amount of energy that is released when making the bonds.
What is the enthalpy of no?
90.25 kJ/mol
Introduction
| Compound | ΔHfo |
|---|---|
| HF(g) | -271.1 kJ/mol |
| NO(g) | 90.25 kJ/mol |
| NO2(g) | 33.18 kJ/mol |
| N2O4(g) | 9.16 kJ/mol |
Why is the enthalpy of H2 zero?
For H2 enthalpy of formation is zero, because it already is the most elementary form. In the problem, however, it’s talking about hear of combustion, which is different — Hydrogen does release heat.
What is the standard enthalpy of formation of oxygen gas?
0 kJ/mol.
Note that because it exists in its standard state, the standard enthalpy of formation for oxygen gas is 0 kJ/mol.
Is enthalpy change of formation always exothermic?
Note that while the majority of the values of standard enthalpies of formation are exothermic, or negative, there are a few compounds such as NO(g) and N2O4(g) that actually require energy from its surroundings during its formation; these endothermic compounds are generally unstable.
Is enthalpy of combustion the same as enthalpy of formation?
By definition, enthalpy change of formation is the enthalpy change when one mole of substance is formed from its elements in the standard state. By definition, enthalpy change of combustion is the enthalpy change (or energy released) when one mole of substance is completely burnt in excess oxygen.