Chemistry, 17.12.2019 05:31 anonymous1813

Which substances have ah = 0 kj/mol

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Answer from: kakkakak4696

Oxygen, bromine, iron, helium

Explanation:

$\Delta H^o_f$ is defined as the standard enthalpy of formation. By definition, the standard enthalpy of formation is equal to 0 kJ/mol for the substances in their standard states, that is, at room temperature and 1 atm pressure.

Simply speaking, looking at the substances given, we need to understand whether their states agree with what we expect to see at standard conditions (e. g., sodium is a metal, fluorine is a gas, bromine is a liquid at standard conditions). Those are substances consisting of just one type of atoms.

Firstly, oxygen is a gas at standard conditions and it is diatomic, so its $\Delta H^o_f=0 kJ/mol$ .Although nitrogen is a gas at standard conditions, it is diatomic, so $\Delta H^o_f\neq 0 kJ/mol$ .Water is a liquid at standard conditions, however, it consists of two types of atoms, hydrogen and oxygen, so $\Delta H^o_f \neq 0 kJ/mol$ .Bromine is a liquid at standard conditions, so $\Delta H^o_f=0 kJ/mol$ .Iron is a solid at standard conditions, it's a metal, so $\Delta H^o_f=0 kJ/mol$ .Helium is a gas at standard conditions, it belongs to noble gases, so $\Delta H^o_f=0 kJ/mol$ .Sulfur is a solid at room conditions, however, the conformation it has is S_8

and not

, so $\Delta H^o_f\neq 0 kJ/mol$ .

Answer from: Quest

vanderwaal's forces of attraction are the electrostatic intermolecular forces that exist in a molecule due to the temporary or permanent dipoles that are developed in a molecule. in $h_{2}s$ , the major intermolecular forces are dipole-dipole interactions as the molecule is polar (bent structure). so the vanderwaal's forces of interaction in between $h_{2}s$ molecules are the permanent dipole-dipole interactions that develop due to the dipole that exists in between the polar h - s bond. the positively charged hydrogen atom is attracted towards the negative end of the dipole that is sulfur of the adjacent $h_{2}s$ molecule. therefore, these forces of attraction are relatively stronger than that of london dispersion forces that exist in non polar molecules.

Answer from: Quest

Coal i believe hope this

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Which substances have ah = 0 kj/mol
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