Select all of the following that have a standard enthalpy of formation equal to zero at 25°C and 1.0 atm?
Si (s)
H20 (1)
N2 (g)
Al (s)
CH4 (g)
H2O(g) Br2 (l)

What is the number of moles in 15.0 g ash3?

Americium-241 undergoes fission to produce three neutrons per fission event. if a neutron-absorbing material is mixed in with this sample so that the rate of neutron production drops down to 1.8 neutrons per fission event, which will be effective at achieving a critical mass? check all that apply. remove a deflective shield surrounding the sample. remove absorbent material mixed in with the sample. compress the sample of americium-241.

Suppose you mix one mole of sulfuric acid (h2so4) with 1 mole of sodium hydroxide(naoh). why does the ph of the solution remain below 7? ( explain so i can get better understanding! )