How are natural elements different from other elements ?

Synthetic elements are man-made elements. ... Synthetic elements are unstable chemical elements and they are not naturally found on the earth. These elements are synthesized in the laboratory. All of them are unstable and radioactive in nature, which means they emit radiations and decay into other elements.

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.