After three half lives have passed, there would be only 12.5 percent of the original amount of a radioactive parent isotope that will remain. Half life is the time needed for a certain amount of a substance to be half its initial amount. It is a common term used in nuclear chemistry describing how fast radioactive substances undergo decay. One half life would correspond to only 50% would be left. Two half lives would be 25% only of the original value. Three half lives would be 12.5%. Four half lives would be 6.25% of the initial value. So on and so forth.
Answer:
the mass of the glass is 2
Probably true because chemicals do control weed and it hurts the environment.
Because of pollution from factories and other activities that release harmful gases into the air
Enthalpy of formation is calculated by subtracting the total enthalpy of formation of the reactants from those of the products. This is called the HESS' LAW.
ΔHrxn = ΔH(products) - ΔH(reactants)
Since the enthalpies are not listed in this item, from reliable sources, the obtained enthalpies of formation are written below.
ΔH(C2H5OH) = -276 kJ/mol
ΔH(O2) = 0 (because O2 is a pure substance)
ΔH(CO2) = -393.5 kJ/mol
ΔH(H2O) = -285.5 kJ/mol
Using the equation above,
ΔHrxn = (2)(-393.5 kJ/mol) + (3)(-285.5 kJ/mol) - (-276 kJ/mol)
ΔHrxn = -1367.5 kJ/mol
<em>Answer: -1367.5 kJ/mol</em>
