A system containing 10 mol of an ideal gas is maintained at thermal equilibrium (at the same temperature) as its surroundings, at a temperature of 50 °C. It then has 100 kJ of heat transferred to it, which causes it to expand isothermally against a constant pressure of 1 atm. It is then isothermally compressed back to its initial volume. What is its change in enthalpy over the entire process? Express your answer in units of kJ.

you need to take a look at the periodic system in order to sort these elements into pairs that would most likely exhibit similar chemical properties. first, you need to find elements that are found in the same group (groups are vertical in the periodic system), and then to see whether they have the same valence number. if they meet these criteria, they will have similar properties.

the first pair: ne (neon) and kr (krypton), are noble gases found in group 8

the second pair: li (lithium) and k (potassium), found in group 1

the third pair: s (sulfur) and te (tellurium), found in group 6

you need to have a picture of the atom that way we can answer it