Why isn’t there a lunar eclipse every time Earth is in between the sun and the Moon?

Is it safe to take 450mg of diphenhydramine hydrochloride?

Why are enzymes important to cells? they bring about chemical reactions. they provide structural support. they form the two layers of membranes. they store large quantities of energy.

Which of the following reactions is endothermic? h2(g) + ½ o2(g) h2o(g), h = -57.82 kcal ½n2(g) + o2(g) + 8.1 kcal no2(g) ½ n2(g) + 3/2 h2(g) nh3(g) + 11.0 kcal c(diamond) + o2(g) co2, h = -94.50 kcal