Students observed rust forming on a bar of pure iron. Which of the following provides evidence that the change to the iron bar was a chemical change?The melting point of pure iron is approximately 1,500C. The mass and the volume of the rust can be measured. The iron bar is able to conduct electricity even after rust forms. The rust is a new substance that is not pure iron.

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it is the most commonly accepted one

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.