9. Explain why you can't write the formula of the ionic compound that forms between Fe
and S?

See explanation

Explanation:

According to Fajan's rules, the degree of covalent character of a bond depends on the relative polarizing power of ions.

Generally, ions become more polarizing when they are small and highly charged. Large negative ions are more polarizable than small ones.

A very small positive charge concentrated on a small area such as in Fe^2+ makes the ion highly polarizing. Also, a large negative ion such as S^2- is highly polarizable.

As a result of these FeS has considerable covalent character hence we can not simply write the formula of the ionic compound that forms between Fe and S?

i think it is true since you can test the answer and can use observations to complete it.

the enthalpy of formation of water is given as -285.8kj/mol, which states that the enthalpy of formation is negative.

negative enthalpy of formation indicates that the heat is released during the reaction process. the heat is released from reaction to the surroundings the enthalpy is expressed with a negative sign with the energy given out in the reaction process.

the formation of water takes place by giving out heat which is -285.8 kj/mol.