An ideal gas does not exist.

an ideal gas does not exist except as a conceptual notion, an ideal. Physicists and chemists idealized the behaviour of real gases so that they could explain these phenomena. Under conditions of low pressure and high temperature, all gases behave like real gases, even gases such as UF6 .

6.4 cm (max) - 25 cm (min)

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.