Heat content of a system is equal to the enthalpy only for a system that is

Heat content of a system is equal to the enthalpy only for a system that is constan "pressure"

Explanation:

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since the atomic number is the number of protons in the nucleus, as we move to the left on the periodic table, the electrostatic pull between the nucleus and the valence electron shell decreases. as we move down a group (vertical column), the valence shell energy level gets further and further from the nucleus.