Determine how many kilojoules are absorbed when 320 g of Ca(OH)2 reacts via the following reaction: Ca(OH)2(s)→CaO(s)+H2O(l),ΔH=+65.3kJ

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Radon-222 or rn-222 has a half-life of 3.82 days. to determine the fraction of an original sample of rn-222 that remains unchanged after 7.646 days, we calculate the amount of rn-222 remaining after 7.646 days and divide it with the original amount. using 1 gram as a basis and using half-life calculation methods, we can determine that  0.249 or 0.25  grams of rn-222 will remain, and thus the fraction remaining is 0.25 or 1/4.

Neptunium is the only of those 4 that doesn’t occur naturally.