Gas is squeezed into a small container is it compressibility or heat of combustion

Squeezing a gas into a small container is an example of compressibility (a physical change).

You measure the heat of combustion (a chemical change) when something burns.

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.