Classify each reaction as endothermic or exothermic.

h2 + br2 → 2hbr, δh = -73 kj
2nh3 → n2 + 3h2, δh = 92 kj
ch4 + 2o2 → co2 + 2h2o, δh = -890 kj
2hcl → h2 + cl2, δh = 184 kj

H2 + Br2 → 2HBr, ΔH = -73 kJ    Exothermic

2NH3 → N2 + 3H2, ΔH = 92 kJ     Endothermic

CH4 + 2O2 → CO2 + 2H2O, ΔH = -890 kJ     Exothermic

2HCl → H2 + Cl2, ΔH = 184 kJ         Endothermic

tracks, burrows, eggshells, nests, tooth marks, or gastroliths

answer:

the answer is 6 valence electrons.

explanation:

valence is the # of electrons on the outer most shell of an atom.

oxygen has 6.

although, the valency of oxygen is 2, because it only needs to make 2 covalent bonds, or gain 2 electrons, to achieve the stable octet configuration of a noble gas.

that's it!

if you need further assistance, let me know: )

~ trueboss72